Mm --—--°V"‘°“‘ “"‘S‘ _ ,, 25¢ nel- (lav maifimmwwa PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE ? 1 "£37.33; £12" ‘1 2 MSU Is An Affirmative Action/Equal Opportunity Institution . emana-m ABSTRACT A CLIMATOGRAPHY or MICHIGAN by Thomas Eugene Niedringhaus Climatography comprises quantitative and qualitative description of the climate for a given area. It involves analysis of genetic fac- tors, individual climatic elements, the relationships which exist between controls and elements, and a synthesis of the foregoing inves- tigations into a classification of climatic types. It is the purpose of this study to develop a climatography for the state of Michigan. The genetic factors are the major atmOSpheric and locational- terrestrial variables that control Michigan's climate. The atmos- pheric factors that are analyzed include the general circulation, water vapor flux, the quasi-stationary action centers, migratory cyclones and anticyclones, air masses and fronts, and synoptic weather types. The general climatic patterns of the study area are shown to be strongly influenced by upper air flow (zonal or meridional), the steering of air masses by the Bermuda and Canadian Highs, the prevalence of migra- tory cyclones and anticyclones, and the movements of the polar front. The second part of the study is concerned with the spatial and temporal behavior of climatic elements. Thermal elements, precipita- tion elements, other moisture indices, and winds are described and their areal distributions analyzed. The parameters that are established include means, extremes, variabilities, and frequencies. The effects Thomas E. Niedringhaus of the Great Lakes are discussed, and they are shown to be locally significant modifiers of several climatic elements. The relationships between selected climatic elements and atmos- pheric controls are examined in part three. Frequency studies of genetic factors are also included in this section. Climatic elements are combined with the atmOSpheric factors with which they are temporally associated, and the results are subjected to statistical analysis in order to establish elemental parameters for the controls and to make inferences concerning the uniqueness of the genetic factors. Signifi- cant conclusions derived from these analyses are: (l) continental polar (cP) air masses occur more frequently throughout the year than any other type; however, continental arctic (cA) is important during winter and maritime trapical ONT) in all other seasons; (2) the North- ern High to the South of the Great Lakes (an) is the synoptic weather type normally associated with very low temperatures, while the North- ern and Eastern Highs (n&eH) system and the Alberta Low to the North of the Great Lakes (aLn) produce warmer than average conditions; and (3) the synoptic types yielding the largest amounts of precipitation are the Montana Low through the Lakes (le), the Southern Low through the Lakes (8L1), and nGeH. In part four the relationships between selected climatic elements and locational-terrestrial factors are investigated by means of regres- sion and correlation analysis. Correlation coefficients show that the strongest relationship exists between temperature and the locational- terrestrial factors, the weakest between precipitation and the latter, with snowfall being intermediate. Partial correlation coefficients reveal that latitude has the highest degree of relationship to spatial Thomas E. Niedringhaus variations of the climatic elements, and elevation and distance from a Great Lake are also significantly associated with elemental differences. The mapping of residuals from regression indicates that the unexplained variance in climatic elements is regionally distributed, with, in gen- eral, the Upper Peninsula being divided into eastern and western segments and the Lower Peninsula being divided into northern and southern sections. The study is concluded by synthesizing the results of the fore- going analyses into a system of climatic regions. The classification consists of four orders of magnitude, namely: (1) the climatic (or planetary) zone; (2) the macroclimatic region; (3) the mesoclimatic province; and (4) the mesoclimatic subprovince. Michigan is shown to be within the circumpolar westerly planetary zone, to be a part of the humid microthermal (D—type in the Koeppen system) macroclimatic region of North America, and to comprise three mesoclimatic provinces. The mesoclimatic provinces are: (l) the Southern Lower Peninsula Transi- tional Province; (2) the Northern Lower Peninsula-Eastern Upper Peninsula Lacustrine Province; and (3) the Western Upper Peninsula Highland Province. The provinces are divided into subprovinces, and the principal climatic characteristics of each are described. A CLIMATOGRAPHY OF MICHIGAN By Thomas Eugene Niedringhaus A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geography 1966 ACKNOWLEDGEMENTS Many individuals in addition to the author contributed to the completion of this dissertation. Dr. Lawrence M. Sommers, head of the Department of Geography, Michigan State University, helped signifi- cantly through his assistance in obtaining financial support. Dr. Donald Blome, Department of Geography, Michigan State University, and Dr. Arthur Getis, Department of Geography, Rutgers University, were generous with their time and advice in assisting with problems of statistical analysis. Dr. Blome, in particular, was most helpful in solving problems connected with the regression and correlation analyses of Chapter IV. Mr. A. H. Eichmeieg.Climatologist of the State of Michigan, and various other individuals in his office, furnished data and reference materials not readily available through the normal sources. Dr. Dieter H. Brunnschweiler, Department of Geography, Michigan State University, the major advisor for the dissertation, made contributions too numerous to be prOperly credited in this short space. It is the author's hape that his extensive and intensive knowledge of climatology is reflected to at least a small degree in this paper. Finally, the author wishes to thank his wife, Bette, whose moral support was an invaluable aid in the completion of the dissertation. ii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS................................................ ii LIST OF TABLES.................................................. vii LIST OF ILLUSTRATIONS........................................... viii LIST OF APPENDIXES.............................................. x INIRODUCTIONOOCOOCOOCOOOOOO0.0.0.0...OOOOOOOOOOOOOOOOOO000...... 1 Statement of Problem 1 Availability of Data 1 The Study Area 2 Chapter I. GENETIC FACTORS AFFECTING THE CLIMATE OF MICHIGAN....... 5 Locational and Terrestrial Factors 5 Latitude 5 Relative Location 6 Lacustrine Controls 7 Tapography 10 The Atmospheric Factors 12 The General Circulation 12 Water Vapor Flux into Michigan 16 Quasi-Stationary Action Centers 17 Migratory Cyclones and Anticyclones 20 Air Masses and Fronts 23 Synoptic Weather Types 26 Conclusion 29 II. THE SPATIAL AND TEMPORAL BEHAVIOR OF CLIMATIC ELEMENTS IN MICHIWO..OOOCOOOOOOOOOOOCOOO0.00000000000000000.. 30 The Thermal Elements 30 Mean Annual Temperatures 30 Mean Temperatures of the Mid-Season Months 33 January 33 April 35 July 35 October 36 Mean Annual Maximum and Minimum Temperatures 36 Temperature Extremes 38 iii TABLE OF CONTENTS (CONT.) Chapter Frequencies of Days Above, Below, or Between Certain Threshold Temperatures Temperature Variability The Spatial and Temporal Behavior of Precipitation Mean Annual Precipitation Mean Monthly and Mean Seasonal Precipitation Winter Spring Summer Fall Mean Frequency of Days with Precipitation Equal to or Greater than .10 Inch Precipitation Variability The Temporal Precipitation Regime The Distribution of Mean Annual Snowfall Solid Precipitation other than Snow Hail Freezing Rain Moisture Elements other than Precipitation Humidity Cloudiness Fog Winds and Tornadoes Surface Winds Tornadoes (High Velocity Wind Systems) Effects of the Great Lakes on Climatic Elements III. THE RELATIONSHIPS BETWEEN SELECTED CLIMATIC ELEMENTS AND AMSPHERIC CONTROISOOOOCOCOO0.000000COOOOOOOOOOOO Frequencies of Migratory Cyclones and Anticyclones Relationships between.Air Masses and Climatic Elements Air Mass Frequencies Temperature Characteristics of Air Masses Precipitation Characteristics of Air Masses Frequency of Frontal Activity Relationships between Synoptic Weather Types and Climatic Elements Synoptic Weather-Type Frequencies Temperature Characteristics of Synaptic Weather Types Precipitation Characteristics of Synoptic Weather Types Analysis of Combined Cyclonic and Anticyclonic Weather Types Association of Air Masses, Synoptic Weather Types, and Climatic Elements iv Page 39 43 44 45 47 47 47 51 53 55 55 59 64 67 67 69 70 7O 70 74 75 75 79 81 88 88 91 92 96 100 106 108 109 114 122 126 129 TABLE OF CONTENTS (CONT.) Chapter IV. THE RELATIONSHIPS BETWEEN SELECTED CLIMATIC ELEMENTS AND TERRESTRIAL CONTROIS...OOOOOOOCOOOOOOOOOOO.00...O. Relationships between Mean Monthly Temperature and Selected Terrestrial Variables Relationships between Mean Monthly Precipitation and Selected Terrestrial Variables Relationships between Mean Monthly Snowfall and Selected Terrestrial Variables Summary and Conclusions Analysis of Residuals from Regression Residuals from Regression for Mean Monthly Precipitation Winter Spring Summer Fall Conclusions Residuals from Regression for Mean Monthly Snowfall Residuals from Regression for Mean Monthly Temperature Conclusions V. THE CLIMATIC REGIONALIZATION OF MICHIGAN................ The Climatic Zone The Macroclimatic Region Mesoclimatic Provinces and Subprovinces Description of Mesoclimatic Provinces and Subprovinces The Southern Lower Peninsula Transitional Province The Genetic Pattern The Elemental Pattern Southern Lake Michigan Lowland Subprovince Southern Lower Peninsula Interior Subprovince Thumb Upland Subprovince Erie-St. Clair Lowland Subprovince Saginaw Lowland Subprovince The Northern Lower Peninsula-Eastern Upper Peninsula Lacustrine Province The Genetic Pattern The Elemental Pattern Northern Lake Michigan Lowland Subprovince Central Lower Peninsula Interior-Transition Subprovince Northern Lake Huron Subprovince Southern Lake Huron Subprovince Northern Upland Subprovince Page 138 141 144 147 151 153 154 154 158 159 160 162 166 170 174 176 176 178 184 187 187 187 188 189 190 191 191 192 193 193 195 196 197 197 198 199 omoleavwvlmoan-Il-Oo'nnn-a'o-t I ale-oeolIIO-IIUI TABLE 0}? CONTENTS (CONT.) Chapter Page Western Northern-Upland Subprovince 200 Eastern Upper Peninsula Subprovince 200 Munising-Grand Marais Subprovince 201 East-Central Upper Peninsula Interior Subprovince 202 The Western Upper Peninsula Highland Province 202 The Genetic Pattern 203 The Elemental Pattern 204 Ishpeming-Escanaba Transition Subprovince 205 Keweenaw Bay4Western Lake Superior Lowland Subprovince 206 Western Northern-Highland Subprovince 207 Huron Mountains Subprovince 208 Western Upper Peninsula Interior Subprovince 208 BIBLImRAmYOOOOOOOOOOOOOOO00......OOOOOOOOOOOOOOOOOOO0.0.0.0... 21]- vi ................................................... 12. 13. 14. 15. 16. 17. 18. LIST OF TABLES Source Regions, Trajectories, and Characteristics of Air M88868 Affecting MiChiganOOOOOO00.000.00.000...0.0000 Mean Number of Days with Dense Fog......................... Prevailing Wind Directions According to Air Mass Type...... Seasonal Effects of Lake and Land on the Climate of MiChiganoOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO0.0000...... Low and High Pressure Systems Passing Through Michigan..... Frequency and Percentage of Occurrences of Air Mass Types.. Means, variances, and Standard Deviations for Temperatures Of Air Mass Types..0..0000.000000000000000000000000000000 Precipitation Frequencies for Air Mass Types............... Total and Average Precipitation for Air Mass Types......... Frequency of Frontal Passages in Michigan.................. Frequencies of Synoptic Weather Types at Five Selected StatioDSOOOO0.0...0.0.0....0.0000000000000000000000000..O Temperature Means, Variances, and Standard Deviations as Related to Synaptic Weather Types........................ Total and Average Precipitation for Synoptic Weather Types. Synoptic Weather Types, Associated Air Masses, and Values of Selected Climatic Elements for Detroit................ Correlation Coefficients between Mean Monthly Temperature and Selected Terrestrial Variables....................... Correlation Coefficients between Mean Monthly Precipitation and Selected Terrestrial Variables....................... Correlation Coefficients between Mean Monthly Snowfall and Selected Terrestrial Variables........................... Orders of Magnitude in Climatic Classification............. vii Page 24 75 78 83 89 93 97 101 103 107 110 115 123 130 142 145 148 177 . - . o - . . a . , u . . u . . . - u . I . Figure 10. 11. 12. 13. 14. 15. 16. 17. 18. LIST OF ILLUSTRATIONS Weather Station Index.................................... Elevation and Station Network............................ UppereAtmospheric Circulation............................ Centers of Action, Air Masses, and Frontal Zones......... Principal Tracks of Pressure Centers..................... Synoptic Weather Types for Michigan...................... Mean Annual Temperatures................................. Mean Temperatures of the Mid-Season Months............... Mean Annual Maximum, Mean Annual Minimum, Absolute Maximum, and Absolute Minimum Temperatures............. Mean Frequencies of Days Above or Below Threshold TemperatureS.....o............................oo....... Mean Length of Period between Last 32° F. Temperature in Spring and First in FaIIOOCOOOOOCCCOOCCCOOCCOCCCCOCCOOC Mean Ame]. FreeipitationOCOOOOOOOOIOOCCOOO0.00.00.00.00. Mean December, January, February, and Total Winter FreeipitationOOOOOOOOOOOOOOOOOOOOOO...OOOOOOOOOOOOOOOOO Mean March, April, May, and Total Spring Precipitation... Mean June, July, August, and Total Summer Precipitation.. Mean September, October, November, and Total Fall Freeipitation0.0000000000000000000000000000000000000000 Mean Number of Days with Precipitation Equal to or Greater than .10 InChoooooooooooooooooooocooooooooooooo Coefficient of variation for Mean Annual Precipitation... viii Page 14 19 21 27 32 34 37 40 42 46 48 50 52 54 56 58 - . . a . u n . u u u . . . . ~ 0 o u - -. o- o- o- o- .o .. .1 - . . a . o u . o . . n . u Figure 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. LIST OF ILLUSTRATIONS (CONT.) PreC1p1tation Regimes...0.000000000000000ooooooacoooccooc Mean Annual SHOWfallocccocoooooccooococoa-cococooooecoooo Prevailing Wind Directions and Tornado Tracks............ Seasonal Modifications of the Great Lakes on the Climate Of M1Chiganoooooccoccocoaccocoaococooocooocooccococccco Residuals from Regression: The Regression of Mean Monthly Precipitation on Distance from a Great Lake, Latitude, and Elevation (December, January, February, MarCh, April, and MaY)ocooccocoa-cocoa.cooccoccooccccoo Residuals from Regression: The Regression of Mean Monthly Precipitation on Distance from a Great Lake, Latitude, and Elevation (June, July, August, September, October, and November.................................. Residuals from Regression: The Regression of Mean Monthly Snowfall on Distance from a Great Lake, Latitude, and Elevation (November, December, January, February, “fireh, and April)............................ Residuals from Regression: The Regression of Mean Monthly Temperature on Distance from a Great Lake, Latitude, and Elevation (December, January, February, MBrCh, April, and “aY)ocococcooocoooooococcocooooooococ Residuals from Regression: The Regression of Mean Monthly Temperature on Distance from a Great Lake, Latitude, and Elevation (June, July, August, September, OCCODEI, and November)............o.................... Climatic Regions of Eastern America...................... Climatic Provinces and Subprovinces of Michigan.......... ix Page 61 65 76 82 155 156 167 171 172 181 182 .o..-.-. ..n.---.---v IeQn-uo \ ...o...--o- .u......... ....u .sa.--. ...1 ,....... ...4.......-.-- waceoonllI s.‘-.o . ,,..... A govt-IIOVOO LIST OF APPENDIXES Appendix Page A. Lists of Stations Used in Temperature, Precipitation, and Regr88810n Analysesooococooococc0.000000009000000... 218 B. Tables Summarizing Difference of Means and Chi-Square Tests Of Chapter IIIOOOOOOOOOOOOOO...0.0.0.0000...0.0... 224 C. Explanation of Regression and Correlation Analyses of Chapter IVOOOO.0...OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 229 Ian-o . c ' a a . ..-. 0.. oc- INTRODUCTION Statement of Problem Climatography comprises quantitative and qualitative description of the climate for a given area. It involves systematic and correla- tive analyses of individual climatic elements and investigations of their relationships to locational-terrestrial and atmoSpheric factors. In contrast to many other states, a climatography of Michigan has not yet been written. It is the purpose of this study to fill this gap by evaluating the available climatic record of the state as follows: 1. descriptive analysis of genetic factors with special emphasis on meteorological element complexes (general atmospheric circulation, pressure systems, air masses and fronts, and synoptic weather types), and discussion of climatically relevant locational-terrestrial factors; descriptive and inferential analyses of individual climatic elements (temperature, hydrometeors, and winds); correlation analyses, with climatic elements and genetic factors as parameters; and classification of climatic types. Availability of Data The data used in this study are from official records of the 2 United States Weather Bureau. The network of stations is shown in Figure 1.1 In general, the network is composed of sites having con- tinuous observations for the period 1931-1960. Different combinations of stations appear in some sections of the paper because of the nature of the analysis or the absence of suitable data. In the air mass and weather type analyses, the network is limited to the five stations appearing on the Daily Weather Map because these genetic phenomena are meteorologically similar over short distances. The correlation analyses are based on stations for which weather records on punched cards are available (see Appendix C). In addition to an observation period of sufficient length, two other prerequisites had to be met by each station: (1) the records must be homogeneous, i.e., a sample from a single population (this may normally be assumed if the station has not been moved to a new location and the instrument exposures have not been fundamentally changed);2 and (2) the selected stations must be as evenly distributed over the study area as possible. The Study Area The area selected for this study is the territory comprising the state of Michigan. Michigan is located in the east-central section 1See Appendix A for lists of stations used in temperature, precipitation, and regression and correlation analyses. 2For a summary of information on substation locations, elevations, exposures, instrumentations, records, and observers from the year each station was established and through 1955, see U.S., Dept. of Commerce, Weather Bureau, Substation History: Michigan, Washington, D.C., 1956. MICHIGAN WEATHER STATION EAGLE INDEX macs . ._07° 0 mmou 030M000: Um: MIMI l smug on 0 "W0 3 new Immune WW _/~. \omomcoo o as rm 0 . ' \J T, OIUNISIN. ugwxgfiy SMILT STE. VIE I ~\ ~ QUITEMET CHAT“ 00'.“ 0 gig ~ «was: \ \ OREXTON ‘~ . ~ \ osuuswsn V \ “f- OWLL . § .7 )0 G \ mo" Imus'nous o 0: 7°” ' C9 nouns": $0 (a \ \ t n 9 Oman AI CITY 2 3°“ .‘ nuns- Q - LLsrou cursors»: j . sack uv o Imam ’ 4 0 (,3 / r‘ i ° , /’ am mom a Q I" .” OEASY .. a Joanna rs: CITY 0 IIOo emu O ' mung MISVILLE "E outsells L LM! 0 can wear osou. O O “8 OM 000000070“ "7"" omusrrs on" ‘- OLUDINOTON tvm ocuowm 0 MO mnos on“, 0 IT. stream ““8“" was 0 suns mums 0 .mm OMENVILLE owosso b“. 06.32: IONI‘O o sumo .nmos rm 0 Quinn“ HOLLAIO “310".” O FIRST-ORDER STATION surest: 0mm: 0 O SECOND-ORDER STATION , . .Loo‘mm Ow“ o SUBSTATION , o 0 us: 0 OMTTLE 0 "'10” Ml“ O'I“ . um nu mart Oceanus cum: I'VE” ONILLSOALE 0mm“ -———-—-—-'L’—.__—_——- o to so so so :00 t I l L 4L J nuts I... 1 I: a, loss I”. Figure l 4 of North America (see inset map on Figure 2). The general situation of the study area may be called mid-latitude-continental. Physiographically, the state is divided into two main peninsulas which are enclosed by four of the Great Lakes of North America. The isthmuses of both peninsulas are oriented toward the south. The northern peninsula is referred to in this text as the Upper Peninsula and the southern is called the Lower Peninsula.1 The entire Lower Peninsula and the eastern half of the Upper Peninsula are parts of the Central Lowland physiographic province which, topographically, is an extensive area of plains. The western Upper Peninsula is a part of the Laurentian Upland, a more elevated area having somewhat greater local relief than the Central Lowland portion of the state.2 A more detailed examination of the relationship between locational- terrestrial factors and the climate of the study area is provided in Chapter I. The selection of the study area was made on the basis of three principal criteria: (1) the lack of previous, detailed investigations; (2) the unusual climatic characteristics of a mid- latitude, continental area enclosed by large, inland water bodies; and (3) the availability and suitability of data. 1These terms, although incorrect in a strictly geographic nomenclature, are so entrenched in common language that their use in a scientific context seems justified. 2See Wallace W. Atwood, Physiggraphic Provinces of North America, (Boston: Ginn and Co., 1940) Pp. 185-228. CHAPTER I GENETIC FACTORS AFFECTING THE CLIMATE OF MICHIGAN The genetic factors that affect the climate of Michigan may be divided into two major groups for analytical purposes. These are: (l) the locational and terrestrial factors; and (2) the atmoSpheric factors. Locational and Terrestrial Factors Latitude Michigan has a latitudinal extent of nearly 6° with its southern and northern boundaries lying at 41° 45' N. and 47° 30' N, respectively. Its mid-latitude position is reSponsible for the large annual varia- tions in zenithal sun angle and length of daylight period. Along the 45th parallel, for example, the noon altitude of the sun is 68350 at the time of the Northern Hemisphere summer solstice, and 213° at the time of the winter solstice. Length of daylight period along the same parallel changes from 15 hours and 37 minutes at the summer solstice to 8 hours and 46 minutes at the winter solstice.1 Latitudinal extent also causes small, but significant, regional differences in sun angle and length of day. For instance at the summer solstice, length of 1Glenn T. Trewartha, An Introduction to Climate, (New York: McGraw-Hill, 1954) Pp. 8-9. day at the state's southern extremity is 15 hours and 15 minutes while in the extreme north it is 45 minutes longer. A constant sun angle variation of approximately 6° exists between the north and south extremities. Thus, the amount of insolation received at the edge of the atmosphere above the study area differs greatly between summer and winter, and to a slight degree during any given season between north and south. The mid-latitude position of the state is reflected in the high degree of weather changeability. Lying in the zone of prevailing westerlies, the study area is subjected to constantly changing circulation patterns, while the migration of the polar front brings the area alternately under the influence of polar and tropical air masses. Relative Location Continental location is a major control of Michigan's climate. No ocean lies within 500 miles of the study area, and westward and southward the distances are much greater. To the west, 2,000 miles separate the state from the Pacific Ocean. To the east, the Atlantic Ocean is only about 500 miles away, but it lies leeward of the state with respect to prevailing winds. The Gulf of Mexico is about 1,000 miles due south of the study area; if circulation is meridional (i.e., south-to-north) tropical air masses from this source region can easily reach the Great Lakes area. The nearest large water body to the north is nearly 500 miles distant; although extensive, Hudson Bay is nearly surrounded by land, is frozen during the winter, and, unlike the Gulf of Mexico, does not represent an air mass source region. Thus, it exerts only a negligible influence on the climate of the study area. The Western Cordillera of North America reinforces continentality by protecting areas on its lee (eastern) side from Pacific maritime influences. Between the study area and the Atlantic Ocean, the Appalachian Highlands stand as a lower, but not insignificant, barrier to the occasional westward movements of maritime air masses. No simdlar barriers block the movement of air masses into the study area from either the north or the south. The depression of the Mississippi River valley allows air originating over the Gulf of Mexico to penetrate deep into the interior of the continent without modification by orographic effects. To the north, air masses from the arctic area of Canada move toward the state with little retardation or modifica- tion by mountain barriers. Lacustrine Controls The two main peninsulas that compose the territory of the study area have their bases toward the south, and these are rather wide in relation to the total areas of the peninsulas, with both bases measuring about 170 miles. The extent of water surface separating the main peninsulas from other land areas rarely exceeds 200 miles,» and throughout most of the state is considerably less. Yet, the water bodies surrounding these peninsulas, namely, Lake Superior, Lake Michigan, Lake Huron, and Lake Erie (and much less importantly, Lake St. Clair) significantly modify the climate of the adjacent areas. Only a relatively small part of the land area of Michigan is more than 75 miles from one of the Great Lakes, and over half of its area is within 50 miles. Because of the 3,235 miles of shoreline, 8 an appreciable part of the study area lies within a few miles of Lake water. However, the climatic modification that each Lake exerts on the adjacent land depends not only on distance between land and water, but also on the Lake's size, shape, depth, and position relative to prevailing winds (see Figure 2). The influence of the Lakes on land is not direct; it is transmitted through the meteorological modifica- tions of air masses that pass over the water bodies before reaching the study area. Lake Superior is the largest, most northerly, and deepest of the Great Lakes. Its long axis is east-west (350 miles), but it has considerable north-south extent also (160 miles). The Lake's shape is complicated by the Keweenaw Peninsula which juts out almost to its center. With a water surface of approximately 30,000 square miles, Lake Superior is over half the size of the entire land area of Michigan. Lake Michigan, which occupies the windward position with respect to the Lower Peninsula, has a north-south axis, and its shape is more elongated than that of Lake Superior. The west-east dimensions of the Lake vary from about 50 miles in the south to 100 miles in the north. Air masses traveling meridionally may traverse 300 miles of water before reaching land. The shoreline is relatively straight, particularly in the south. In the north, the Door Peninsula of Wisconsin and the Leelanau Peninsula of Michigan cause irregularities in shape. Lake Huron, like Lake Michigan, has a north-south axis (220 miles), but is not as elongated. It has a greater east-west extent MICHIGAN ELEVATION AND STATION NETWORK wk,” '- ELEVATION (FEET) D 570 - COO COO-IOOO D IOOO-IZOO IZOO-IOOO I “00-2000 0 WEATHER STATION “‘4' Arie/044,, ss- r.r.u.. was 1 Figure 2 10 (180 miles) and a more irregular shape than does its western counter- part. Lake Huron's shape is complicated by the mcgepn‘ia 1a and Manitoulin Island in Ontario, and by the indentation of Saginaw Bay to the southwest. Lake Erie, like Lake Superior, has an eastdwest axis; however, it is only one-third the size and considerably shallower than the northern Lake. Both Lakes Erie and Huron lie to the east of the study area, or leeward with reapect to prevailing winds, while Lakes a! Superior and Michigan have positions on the windward side. 12222222112 Topographic elements of direct climatic significance are elevation, local relief, and orientation of landforms. With regard to absolute elevation, the state may be divided into lowlands, uplands, and highlands.1 These are shown in Figure 2. The lowlands generally border the Great Lakes and have elevations from 570 to about 900 feet. The principal lowland regions are: (l) the Erie- St. Clair Lowland in the southeastern Lower Peninsula; (2) the Saginaw Lowland surrounding Saginaw Bay in the east-central Lower Peninsula; (3) the Michigan Lowland along the eastern shore of Lake Michigan; (4) the Eastern Lowland of the eastern half of the Upper Peninsula; and (5) the Reweenaw Lowland fringing the Keweenaw Penin- sula in the western Upper Peninsula. There are two upland areas in the state, both in the Lower Peninsula. The uplands are found at altitudes between 900-1300 feet, 2N‘4 1Bert Hudgins, Michigan: Geographic Backgrounds in the Develoggent of the Commonwealth, (Ann Arbor, Mich.: Edwards Bros., 1958), P. 17. 11 with one being located in the north-central portion of the peninsula and the other in the southeastern section, to the northwest of the Erie-St. Clair Lowland. The former is referred to as the Northern Upland (or the High Plains), and the latter is called the Thumb Upland, because it forms the physiographic backbone for the thumb of the mitten-like shape of the Lower Peninsula.1 The western half of the Upper Peninsula is dominated by topography that has elevations between 1200 and 2000 feet. This area, referred to as the Northern Highlands, is the only truly mountainous section of the state. In particular, the Huron Mountains, the Porcupine Mountains, the Gogebic Range, and the Copper Range stand higher than the surrounding terrain, and are the most significant orographic barriers within the study area. Local relief is moderate; at no place within the study area does it exceed 1500 feet, and much lower values are typical. The greatest elevation differences are found in the Northern Highlands in the vicinity of the Porcupine Mountains (along Lake Superior in the extreme west of the Upper Peninsula), the Copper Range (extending southwest-northeast along the Keweenaw Peninsula), and the Huron Mountains (a group of hills between LIAnse and Ishpeming). Here, local relief exceeds 1400 feet in some places, but, over most of the area, is less than 1000 feet. Local relief within the remainder of the state is of less magnitude than that of the Northern Highlands. The principal fea- tures of above average local relief in the eastern Upper Peninsula and the Lower Peninsula are belts of hills which constitute very 1Ibid. 12 irregular, hummocky topography. In most parts of the above areas, however, the hills do not rise more than 200 feet above the surround- ing terrain. Important exceptions are (l) on the rim of the Northern Uplands where relief exceeds 500 feet in a few places, and (2) in parts of the Thumb Upland. Many of these belts of hills are oriented meridionally, and consequently transverse to the prevailing winds. Most of the remainder of the Central Lowlands portion of the state consists of flat or gently undulating plains with no appreciable local relief. However, two additional climatically relevant relief features do occur in some parts of the study area. At many places along Lake Superior the eastern Upper Peninsula has high, cliff-like shores, for example, in the Pictured Rocks area northeast of Munising. In the Lower Peninsula extensive sand dune formations are found along the eastern and southern shores of Lake Michigan, with maximum local relief over 300 feet. Sand dunes with appreciable local relief do not occur on the shores of Lakes Superior, Huron or Erie. The Atmospheric Factors Th; Gegeral Circulation The general circulation is the complex pattern of atmospheric motions that results from the unequal heating of tropical and polar areas and from the earth's rotation.1 The atmosphere over the study area is dominated by a component of the general circulation referred to as the circumpolar westerlies, which may be defined as a tropospheric wind belt, shifting latitudinally from season to season, but always 1Sverre Petterssen, Introduction to Meteorology, (New York: McGrawdHill, 1941) Pp. 98-110. 13 characterized by a west-to-east (quasi-geostrophic) flow of air in a circumpolar orbit.1 Figure 3 illustrates the two basic types of circumpolar westerly circulation which govern the upper air flow over Michigan throughout the year. By means of height contours, wind directions, and temperatures at the 500 millibar level, a zonal flow pattern is contrasted with a meridional flow pattern. The zonal flow map is representative of a winter situation. The winds over the Great Lakes at the 500 millibar level (corresponding to about 18,000 feet in altitude) are oriented almost straight west- to-east, with a consequent westerly flow of air. Colder air at this elevation lies well to the north of the study area, whereas warmer air is found slightly to the south. When this type of circulation prevails, surface temperatures in Michigan are usually near, or slightly above average. The synoptic pattern chosen to indicate meridional flow shows a movement of air from the north to the south. The study area lies near the center of a pronounced trough in the circumpolar westerlies which is causing very cold air to flow over the state with meridional orientation rather than latitudinal. Relatively warm air now lies far to the east, west, and south. Surface temperatures in Michigan are normally well below average during the persistence of the upper trough. The location of upper waves, their season of occurrence, and their mean and extreme periods of persistence, greatly influence the weather and climate of the study area. Zonal flow (high index) may 1Kenneth F. Hare, "The Westerlies," Geog. Review, Vol. 50, No. 3, July 1960, Pp. 345-367. 14 U PPER-ATMOSPHERE CIRCULATION IERIDIONAL FLOW PATTERN ZONAL FLOW PATTERN IEATNII susuu, lulu IIATMEN SOUIOE: u. 0. - I' I u .4 4.: g s :3 - I ‘I' ' ‘ a; I 4: x E a° ° u , . “ 80' u‘ a ' .5: 3... ps1 -u 2 a .5 n: 3 ° 8-4 0" " -u a 54": ES =§§ : I” x°¢ ‘Jnuo u§ tGL §:3= 1. .53: Na —— nsooo— u, S IIATNII IOUIGE: 5 E S I D d 1 o 3' 4 u I a a 3. i i 3' III, JAIUARY 0. “a, In! 15 change into meridional flow (low index), and vice versa, thus causing non-periodic temperature changes. A change from zonal to meridional and again to zonal flow may be referred to as an index cycle.1 Namias2 has stated that the quasi-permanent troughs and ridges of the circumpolar westerlies are anchored in different longitudinal positions in different years, and thus in some years the flow patterns become more highly organized into confluence (high index) bands than in others. In this manner the reservoir of cold polar air in the north is stored or depleted over different time intervals. The intensity of the cycle is thought to depend on net outgoing radiation and length of storage time in the area of the cold air reservoir. Therefore, variations in the character of index cycles from year to year are very likely. This differentiation in the intensity of cycles is one of the chief factors for the high degree of weather variability in Michigan. Another important factor which must be considered in the dynamic climatology of the state is the jet stream. On most flow maps drawn for the 500 millibar level, or higher, bands of high wind velocity can be recognized over the interior of North America throughout the year. It has been shown that the movement of surface weather systems, such as cyclonic centers along the polar front, is governed by the "steering" of jet streams, and that the distribution of precipitation 1For a discussion of high and low indexes and the index cycle see Jerome Namias, "The Index Cycle and its Role in the General Circulation," Journal of Meteorology, Vol. 7, No. 2, April 1950, Pp. 130-139. 2Ibid. 16 bears close relationship to the location and intensity of the jets.1 In winter the zone of strongest jets is located well to the south of the state (25-300 N.), but they are often found over the Great Lakes in the transitional seasons, and reach their northernmost position over southern Canada in summer. While weakened due to the absence of strong temperature contrasts in the upper atmosphere during summer, jet stream activity is conspicuous during Spring and fall, as evidenced by the high frequency of cyclonic and frontal systems passing through the state in these periods (see Chapter III for frequency analyses). In the preceding section of this chapter it was noted that there are no major topographic barriers to the north or south of Michigan which might seriously impede the free movement of air from these directions into the study area. This fact takes on added significance with the knowledge that meridional transfers of air, induced by upper waves and the meanderings of the jet streams, occur with regularity within the framework of the circumpolar westerly circulation. Water Vapor Flux into Michiggg The general circulation is responsible for the movement of water vapor into the study area. The transfer of moisture from the oceans onto the North American continent is accomplished mainly by two well- defined streams: (l) a strong southerly flow from the Gulf of Mexico; and (2) a comparatively weak westerly movement from the Pacific Ocean. 1For discussions of the jet stream see Jerome Namias and Philip Clapp, "Confluence Theory of the High Tropospheric Jet Stream." Journal of Meteorology, Vol. 6, No. 5, October 1949, Pp. 330-336; and Lloyd G. Starret, "The Relationship of Precipitation Patterns in North America to Certain Types of Jet Streams at the 300 Millibar Level," Journal o§;Meteorology, Vol. 6, No. 5, October 1949, Pp. 347-352. 17 These streams of water vapor converge in central North America to form an intense region of outflow extending from North Carolina to the southern coast of Labrador. Of the two major streams, the southerly flow from the Gulf of Mexico makes by far the greatest contribution to water-vapor flux into the study area.1 The net water-vapor transfer from the oceans to the atmosphere over Michigan varies greatly from winter to summer. In winter the aver- age flux ranges from 1600 grams per cubic mile per second in the southeast to a minimum of 600 grams in the northwest. In summer the moisture transfer is more uniform over the area, varying from about 1500 grams per cubic mile per second in the southwest to nearly 2000 grams in the northeastern Upper Peninsula. The southern Lower Peninsula thus has the highest flux during winter and the Upper Peninsula has the highest vapor transfer during summer. For the entire year, however, the southeastern section has the strongest mean flux (1500 grams) and the northwest has the weakest (1000 grams).2 This is reflected in the somewhat greater mean convectional and warm-sector precipitation received in the southern part of the state (see Chapter II). Quasi-Stationary Action Centers The quasi-stationary pressure cells which govern the circulation over the state may be grouped into two general types: (1) the oceanic or planetary cells consisting of subpolar lows (Aleutian and Icelandic); 1George S. Benton and Mariano A. Estoque, "Water Vapor Transfer over the North American Continent," Journal of Meteorology, Vol. II, No. 6, Dec. 1954, Pp. 462-477. 21bid. 18 and (2) the continental or thermal cells which normally have high pressure in winter (Canadian and Basin Highs) and low pressure in summer (Arizona Low). Of these systems (see Figure 4) only the Canadian High and the Bermuda High have both direct and frequent influence over the weather of the study area. Figure 4 clearly indicates the dominance of the Bermuda High over the eastern United States during summer, with its anticyclonic flow of warm, moist tropical air around its western flank into the study area. However, the equatorward migration of the Bermuda system during winter significantly decreases its ability to steer air masses as far north as Michigan. In winter the Canadian High often covers the major portion of the northern interior of the continent. The center of the anti- cyclonic system may lie as far south as the Great Lakes area but even if it is located far to the north, its dominance may extend from the arctic to the mid-latitudes, especially if a low index (meridional) circulation is established. It is the principal action center con- trolling the movement of cold, dry air masses into the study area. The Basin High, occurring during winter over the intermontane area of the western United States, is only indirectly related to Michigan weather as a blocking anticyclone, preventing the entrance of Pacific cyclones to the interior of North America. During fall, winter, and spring, when polar and tropical air masses have substantial temperature differences, air forced southward by the Canadian High may encounter air forced northward by the Bermuda High with the resultant development of a wave disturbance. The subsequent propagation of migratory cyclones, and frontal systems l9 mmmmm >433 NZON hzozuuu_ho¢< wZON h20¢u-K05 Jm4 1mm 24m! -,_3 mMZON 45.201“. oz< .mmmmmo_kz< mKMhzmo mmammmmn. “.0 9.05m... . — L ’ ww2040>o .._ .auos huu> unaoa .oHnouuoo Adam“: .naoa was unease unopfioo teaspoon: u mo>oa ow we season was“ one moans: stucco enouuco nausea moo huaau> «enumnwunwz House: ow no ofiow Hone any ofiwuuuoa HE sconce one nuneoauuoo once was .munaaaoo aneueun .ueeeuam auuoz wuoea demon oeuou< one camwoom unoauunuuoz uoaom oawueuoa ma wowsam nouuo ensues: once one .oouwou wagon Houoooaucoo museums use .noawou coupon «oxen amouo awoousu uumsnunom mvmomo Amuuooounuuoz no he canons was Hooo hHo>auoHoM uoaaam mo coaueuosaa menu uaaoumoo unoHo oeucu we xdmaw ensues: wwwom mmHom Hmu once coo .uwfioa ouoa .uuanmz macaw .m.= ououmooauuoc ou mew Hoodoouucoo we seem sauowucou eminence nouauuu ..m.D :uoumoonu30m ouoH moz some on we we “Hosea .moeeaeno ooowuow mo umnmoua pone no>o maneum ouoa onaoOua use .uanmumco .umfioa .auoz muuoum nomad: .M.z one huHHm> «maemwamwflz smacks» untfiauoz com nonopeuoo one oowxoz mo wane Heoeaoua oawuauma Ha meanness .umwoa .oaoo ou Hooo Am mandamus .umaoa .Hooo Am moHam> uooousoq .um awoounu pumaumusnu50m Am umo3ouuoz oeuwoum mo Hoe lacuna .ummoo owwwomm woo~< A4 season .ALe .eeoo moeoam uuouu .m once moHHu> .m Heawowammwz macaw cumsaunom uHaoum .zuo .uaoo zeoaueuxm muaumwuouooumno z¢UHmon UZHHUHhh< mamm¢z mH< ho mOHHmHMMHU¢m MEAN TEMPERATURE 50' F2, OR HIGHER o 50 m: MEAN TEMPERATURE 40° F., was OR LOWER Iss- 1 lav T.E n, IDES Figure 7 33 shore of Saginaw Bay. Mean temperature decreases from over 48° F. to less than 45° F. within a distance of 50 miles. Although the steep gradient continues westward toward the center of the Lower Peninsula, it is less obvious in the vicinity of Lake Michigan. The crowding of isotherms in this belt represents a marked thermal boundary in the state. Mean Temperatures of the Mid-Season Months Figure 8 shows mean temperatures for the mid-season months of January, April, July, and October. Water isotherms of surface tempera- tures of the Great Lakes are also shown on these maps in order to illustrate thermal differences between land and water during the various seasons.l January.- Mean air temperatures in mid-winter vary from over 28° F. in the southwest to 12° F. in the northwest. The maximum regional temperature contrast is 16 F.°, or about 6 F.° more than for mean annual temperature. The greater regional differentiation for January is indicated by the closer spacing of isotherms. It is notable that water temperatures in the Great Lakes are from 5 to 15 F.° warmer than corresponding air temperatures over the land surfaces adjacent to the shorelines. In all parts of the state, higher temperatures occur near the Great Lakes. For example, the 25° F. isotherm parallels the Lake Michigan shoreline for nearly half the latitudinal extent of the Lower Peninsula. The cells which were observed on the mean annual map like- wise appear on the January map, although shapes and gradients differ. In particular, the cellular patterns of the Northern Highlands and Northern Uplands are indicative of very steep temperature gradients. lLake temperatures taken from U.S., Dept. of Commerce, Weather Bureau, Climatology and Weather Services of the St. Lawrence Seaway and Great Lakes, Technical Paper No. 35, 1959. MEAN APRIL TEMPERATURE ('E) v1...“ vn MEAN OCTOBER TEM’ERATURE VII..- MEAN JANUARY TEMPERATURE PE) 71-.” [or ('E) MEAN JULY TEMPERATURE .Ir Figure 8 35 The Saginaw Lowland still stands out as a warm area and the north- eastern Upper Peninsula appears again as a cold area. épgil,- The range of mean air temperatures for the mid-spring month is from 48° F. in the extreme southern-interior to 36° F. in the northeast Upper Peninsula, for a statewide differential of 12 F.°1 In contrast to January, water temperatures are now from 1 F.° to 9 F.° colder than correSponding air temperatures over the land surface adjacent to shorelines. Thermal patterns differ fundamentally from those of mid-winter, as indicated by the marked poleward bending of isotherms in the Lower Peninsula and the occurrence of higher temperatures inland rather than along the Lakes in both peninsulas. The cellular patterns, which were conSpicuous in January, are now very nearly absent. g2;1,- Mean temperatures during the middle of summer vary from over 74° F. in the southeastern and southwestern Lower Peninsula to less than 63° F. in the northeastern Upper Peninsula, for an areal range of about 12 F.° Water temperatures are from 1 to 16 F.° colder than air temperatures over the adjacent land surfaces. The July temperature pattern is similar to that of April, indicating that the same controls are dominant in both months. Pole- ward bending of isotherms in the Lower Peninsula is a feature of both months, and, although warm and cold cells, corresponding to low and high elevations reapectively, are better marked in July than in April, they are not as well defined as in January. 1Absolute temperatures are stated as OF., differences as F.° 36 October.- The range of mean temperatures in the mid-fall month is from 55° F. in the southwestern Lower Peninsula to 45° F. in three separate areas of the Upper Peninsula, or a difference of about 10 F.° for the entire state. Water temperatures vary from 2 F.° colder to 5 F.° warmer than air temperatures of neighboring shoreline stations. The regional pattern resembles that of January very closely, except that the isotherm gradients are somewhat steeper in the winter month. Temperature differences between October and April are note- worthy, with the mid-fall month being considerably warmer than the mid-Spring month throughout the study area. It is evident from Figures 7 and 8 that the mean annual tempera- ture pattern of the state resembles the January and October maps more closely than those of April and July, particularly in the equatorward- bending of isotherms in the Lower Peninsula and the location and orientation of warm and cold cells. The greater persistence of winter temperature conditions and the greater thermal contrasts over the region during this season may be cited as primary factors for the similarity between winter and annual temperatures. Mean Annual Maximum and Minimum Temperatures Mean annual maximum and minimum temperatures are shown in Figure 9. The highest mean maximum is 61° F. and the lowest is 47° F., for a regional difference of 14 F.° Mean minima range from 43° F. to 280 F. for a maximum regional contrast of 15 F.°, indicating that these parameters are similar in their differences over the study area. In terms of patterns, however, mean minimum and mean maximum temperatures present a marked contrast. Mean maxima resemble the April and July averages, while mean minima correspond to October and l I T MEAN MAXIMUM TEMPERATURE (‘5) i 'l D '0‘! T I ‘Y MEAN MINIMUM TEMPERATURE PHI 1" 1 J.” V ( x was ht? 04 ‘k I Y I I ABSOLUTE MAXIMUM TEMPERATURE (' [I \\o .s “ k " u’.‘ - "1: ca \\0 ."/ io‘ - I02 _0 /§ .00 . ‘ 1n- , 1’" -, ‘4 'I. :00: I I T ABSOLUTE MINIMUM TEMPERATURE ('EI 0" My“) 38 January averages. Mean maximum temperatures are thus highest in the interior and mean minimum temperatures are highest near the Great Lakes. To illustrate, Muskegon, on Lake Michigan, has a mean maximum of about 56° F. while Greenville, 50 miles eastward at the same latitude, has a maximum averaging 2 F.0 higher. For mean minima the corresponding temperatures are 400 F. at Muskegon and 38° F. at Greenville. Temperature Extremes Temperature extremes for Michigan are given in Figure 9. Absolute maximum temperatures (the highest official temperature recorded at each station) range from 110° F. at Mia and Saginaw to less than 980 F. along the shores of the eastern Upper Peninsula. Absolute minima vary from -140 F. in the extreme southwest and southeast to -51° F. in the center of the Northern Upland (Vanderbilt). It is interesting to note that absolute minima in the Upper Peninsula are higher than those in the Northern Upland. The statewide difference in absolute minimum temperatures is much greater than that for absolute maxima (approximately 37 F.° for minima and 12 F.0 for maxima).1 The pattern of absolute maxima is similar to that of mean maxima. The isotherms are bent parallel to the Great Lakes, and higher tempera- tures are observed in the interiors of both peninsulas. Isotherms of absolute minima resemble those of mean minima. They are parallel to the Lakes or form cells, but with the higher values near the water bodies. 1This difference is not readily apparent from observation of the respective maps, because the isotherm interval for maxima is 2 F.° while that for minima is 4 F.°, in order to prevent crowding of lines on the latter map. 39 Frequencies oprays Above, Below; or Between Certain Threshold Temperatures The following analysis concerns frequencies of days above, below, or between certain threshold temperatures. The significant thresholds used in this study are 0° F., 320 F., and 90° F. Four thermal frequency maps appear in Figure 10: (1) mean number of days with a minimum temperature of 0° F., or below; (2) mean number of days with a maximum temperature of 320 F., or below; (3) mean number of days with a minimum temperature of 32° F., or below; and (4) mean number of days with a maximum temperature of 90° F., or above.1 Large regional differences in frequencies occur for all of the above threshold parameters. For "polar days" the values range from 2 days along the Lake Michigan shoreline to over 42 days in the North— ern Highlands. There are only 40 "ice days" in the south but more than 100 in the Northern Highlands. One-hundred and thirty "frost days" in the south contrast with 195 in the western Upper Peninsula, giving the largest regional difference in this series, 65 days. "Tropical days" vary from less than 2 along the Lake shores of the Upper Peninsula to 26 in the southern interior of the Lower Peninsula. The persistence of temperatures over 90° F. shows less regional variability than that of the other temperature conditions, but the statewide difference of 24 days is still appreciable. In all of the threshold analyses it is notable that frequencies increase toward the interior of the study area. Areas adjacent to 1A papular, but descriptively useful terminology for these threshold-frequencies is, respectively: (1) "polar days"; (2) "ice days"; (3) "frost days"; and (4) "trapical days". 40 T I I MEAN NUMBER OF DAYS WITH MINIMUM TEMPERATURE O‘ F. OR BELOW 9! I 3.3 I T T MEAN NUMBER OF DAYS WITH MAXIMUM TEMPERATURE 90° F., OR ABOVE MEAN NUMBER OF DAYS WITH MAXIMUM TEMPERATURE 32'5. OR BELOW "I.tm MEAN NUMBER OF DAYS WITH MINIMUM TEMPERATURE 32' F. OR BELOW 10' l 1.0' 'CI‘ 19.3 Figure 10 41 the Great Lakes have fewer days with extreme temperatures, while stations located inland experience a greater number of days with above or below average temperatures. The former areas may be con- sidered as belonging to a lacustrine type of temperature regime, the latter areas a continental type. Figure 11 shows the length of the frost-free season, here defined as the mean number of days between the last 32° F. temperature in spring and the first in fall. This period varies from over 170 days in the southeast and southwest to less than 70 days in the center of the Northern Highlands. It must be emphasized that in an area of the limited size, latitudinal extent, and elevational differences characterizing Michigan, this large contrast (100 days, or the equivalent of more than three calendar months) is of out- standing climatic significance. The isoline pattern for frequency of frost-free days very closely resembles those of the 0° F. and 320 F. thresholds shown in Figure 10. In the Lower Peninsula most isolines are deflected equatorward over the interior, indicating shorter frost-free periods with increasing distances from the Great Lakes. Gradients are slightly steeper than average near the Lakes, but are steepest in the areas of higher elevation. The Northern Upland cell, for example, is well-defined with its values ranging from about 130 days on its periphery to less than 80 days at the center. In the Upper Peninsula, isolines either parallel the shores or conform to the outlines of the Northern Highlands. The length of the frost-free season varies little along the shores of Lake Michigan and Lake Superior (140 days, except in the extreme west where it 42 __43° T I I MEAN LENGTH OF PERIOD BETWEEN LAST 32”? IN SPRING AND FIRST IN FALL TEMPERATURE FROST-FREE PERIOD I50 DAYS, OR GREATER FROST-FREE PERIOD IOO DAYS, OR LESS lBB‘ iflLES l I“. T E N, I963 Figure 11 43 decreases to 130 days). However, frequencies decrease very rapidly with increasing distance from the shores. The importance of Lake proximity is illustrated by comparison of Fayette-Sack Bay (Upper Peninsula) and Ionia (Lower Peninsula). Both stations have average frost-free seasons of 140 days. Ionia is located 180 miles to the south of Fayette-Sack Bay, but, while the latter is situated on Lake Michigan, Ionia lies 60 miles inland from the shores of the same Lake. Tgmperature Variability For the determination of temperature variability, a sample of 25 stations was selected. variances, standard deviations, and coefficients of variation were computed for mean annual temperature and mean monthly temperatures of the 4 mid-season months (January, April, July, and October).1 The coefficients of variation for mean annual temperature are very low, averaging about 3 per cent for the 25 station sample. Upper Peninsula annual temperatures are slightly more variable than those of the Lower Peninsula, but the differences do not exceed 2 per cent. This indicates little variation in mean annual temperature from year to year at any particular station as well as a small intraregional variability. In January the coefficients of variation are from 5 to 9 times greater than they are for the annual temperatures. Temperature variability is greatest in the northern part of the state during winter, with Ironwood and Stambaugh, for example, having coefficients of over 30 per cent. The lowest thermal variation (about 15 per cent) 1The coefficient of variation is calculated by dividing the standard deviation by the mean and multiplying the quotient by 100. 44 occurs in the south along the Lake Michigan shore at Benton Harbor, Ludington, and Manistee. Somewhat higher variability is found in the interior, with the highest coefficients in the Lower Peninsula occurring in the Northern Uplands at Mia and Cadillac (23 and 25 per cent, respectively). The high variability characteristic of winter disappears during the summer. Coefficients of variation for July are approximately the same as for mean annual temperatures, and at several stations are even lower. The highest variabilities during July are in the North- ern Highlands and Northern Uplands, and the lowest are in the south- eastern Lower Peninsula. In Spring and fall, thermal variances are intermediate between the high variabilities of winter and the low variabilities of summer. In general, spring is more variable than fall; April has a coefficient range from 7 to 11 per cent, while October has a range from 5 to 8 per cent. The Spatial and Temporal Behavior of Precipitation The purpose of this section is to indicate the spatial and tem- poral patterns of precipitation. The investigation is based on a network of 110 stations for which appropriate data are available. This represents a density of one station per 525 square miles, or an average distance of 23 miles between stations. Precipitation is more variable at any given station than is temperature and also varies more over short distance. Unlike temperature, precipitation is a non-continuous variable.1 However, the use of a 30-year period 1Every station (or place) has a measurable temperature on every day of the year. However, precipitation does not occur at any station every day of the year, and is, thus, non-continuous. 45 (l93l-l960) tends to smoothen regional and temporal differences. Mean Annual Precipitation Precipitation falls to the surface of Michigan in several forms, including drizzle, rain, snow, granular snow, sleet, glaze (or freez- ing rain), and hail. In this discussion all of these forms are considered under the general heading of precipitation. Figure 12 indicates the distribution of mean annual precipita- tion. Values range from 36 inches in the southwestern Lower Peninsula and Gogebic Range of the Upper Peninsula to 26 inches on the eastern side of the Northern Upland, a regional difference of approximately 10 inches. A The western sections of the peninsulas are the wettest parts of the study area, particularly where the two isthmuses connect with land to the south. This results in a meridional orientation of the general pattern of precipitation. However, the pattern is complicated considerably by the large number of cells appearing in both peninsulas. Precipitation gradients are moderate in some parts of the state but very steep in others. Steep gradients occur primarily in the Northern Highland, the Chatham-Munising area of the northern Upper Peninsula, the Northern Upland, the southwestern Lower Peninsula, and along the shores of Lake Michigan. The steepest gradients are found in the central Northern Upland where precipitation decreases from 32 inches to 26 inches within a distance of 25 miles. In general, the interiors of the peninsulas have moderate gradients and average amounts of precipitation, while the eastern Lower Peninsula also has moderate gradients but is drier than the interior. 46 I I MEAN ANNUAL PRECIPITATION (INCHES) MEAN PRECIPITATION MEAN PRECIPITATION can. u. 3. venues BUREAU, CLIMATOLOGICAL DATA, GREATER THAN 32 INCHES LESS THAN 2B INCHES IBSI . I960 I”. MILES 04’ TEN. I963 Figure 12 1*7 Mean Monthly and Mean Seasonal Precipitation Winter.- Mean precipitation for each of the three winter months (December, January, and February), and for the three months combined, is shown in Figure 13.1 Mean precipitation at nearly all Michigan stations is lower during winter than in any of the other seasons. Only a few stations on the Keweenaw Peninsula exceed 3 inches precipita- tion for at least 2 of the winter months. Other areas of above average winter precipitation are the southwestern Lower Peninsula (Allegan- Benton Harbor-Eau Claire triangle), the east-west corridor between Milford and Detroit, the small area along the Lake Michigan shore of the northwestern Lower Peninsula, and the northeastern Upper Peninsula. The areas of low precipitation are principally in the interior of the state, although the area around Saginaw Bay and the Upper Peninsula shore along Lake Michigan are also rather dry. Areas of above and below average precipitation are shown by contrasting stipple patterns on the composite winter precipitation map. On the monthly maps the means for December and January are generally higher than those for February.2 Spring.- The spring months (March, April, and May) are marked by a progressive increase in precipitation overthe entire study area, excepting the aforementioned Keweenaw Peninsula. The increase begins in March in the extreme southern part of the state, and advances 1Data represent water equivalent of snow; i.e. one inch of pre- cipitation equals 10 inches of snow. 2December and January, with 31 days each, are 3 days longer than February in 3 of every 4 years and 2 days longer in the fourth year. If this difference in number of days is taken into account, the mean precipitation at most stations in February would not differ signifi- cantly from December and January. 48 MEAN DECEMBER PRECIPITATION “Hm I MEAN JANUARY PRECIPITATION “NONE" numvnm- "In" nu- I Inc-an ulna Figure 13 49 northward during April and May. In March, no part of Michigan averages 3 inches of precipitation. In April, however, the southern quarter of the Lower Peninsula has at least this amount, and during May the 3 inch isohyet moves far enough poleward to enclose all of the study area except the extreme north and northeast. In the latter month 4 inches are recorded for the first time in the calendar year, but only in the extreme southwestern Lower Peninsula. The distribution of Spring precipitation may be observed in Figure 14. During March and April the Upper Peninsula has less precipita- tion than the southern Lower Peninsula, and resembles the northern Lower Peninsula in this reapect. For example, the 3 inch isohyet, which encompasses a sizable area in the Lower Peninsula during April, does not appear in the Upper Peninsula at this time. By May, however, a wedge of heavier precipitation extends into the area from the land bridge to the south. Most of the Upper Peninsula has at least 3 inches of precipitation during the last month of spring. The zonal distribution of Spring precipitation in the Lower Peninsula contrasts with the meridional orientation of annual precipita- tion. In the Upper Peninsula the relationship between mean spring precipitation and latitude is less obvious with the general decrease being from southwest to northeast. The largest totals for spring precipitation in the Upper Peninsula are above 8.5 inches and occur in the southwest. In the Lower Peninsula over 10 inches are recorded in the extreme south-central section. The area of least precipitation lies astride the Straits of Mackinac and in the southeastern Upper Peninsula where less than 6 inches are recorded. 50 I MEAN MARCH PRECIPITATION "NW”, I 1“. VII.” I I I MEAN APRIL PRECIPITATION (mom 1* i ,0“ MIL-Io A 1.. I... III. .0 CHI MOWIYAYIOOI sauna has no menu PRECIPITATI” LI“ 7 menu 1" 1 10“ 'u, no Figure 14 51 Summer.- For all parts of the study area summer is the season of maximum precipitation, as may be observed in Figure 15. June is the wettest of the summer months, as exemplified by the large area with at least 4 inches of precipitation. The areas with the greatest precipitation at this time are the southwestern Lower Peninsula and the southwestern Upper Peninsula. The latter area (particularly in the center of the Northern Highlands) is the rainiest part of the study area in June, and is the only section that has a mean of over 5 inches for any month of the year. During July, mean precipitation decreases throughout most of the state. The important exceptions are (l) a narrow corridor from Marquette southward to Escanaba and Stephenson in the Upper Peninsula, (2) the Grayling area of the Northern Upland, and (3) the Port Huron- Sandusky section of the Lake Huron shore. In each of these areas June and July precipitation are approximately equal. However, for the great majority of stations a decrease in precipitation between June and July is conSpicuous. In August, mean precipitation increases again over most of the study area, but not to the high levels attained in June. The map of mean summer precipitation accentuates the areas of above and below average precipitation. Clearly, the southwestern Lower Peninsula and the western Upper Peninsula are the two principal areas of above average precipitation. Two small cells, one in the vicinity of Grayling in the Northern Upland, the other surrounding Newberry in the eastern Upper Peninsula, are also above average. The two principal areas of below average precipitation are (l) the periphery of the northern Lower Peninsula, including the Saginaw Lowland, and f . I F MEAN JUNE PRECIPITATION (mm 1" 1 luv u..." I I MEAN JULY PRECIPITATION (main) vn,nu u- n-_ was ”Immuno- can": vu- no mean numunon us: run as menu n u A: I Figure 15 S3 (2) the littoral of the eastern Upper Peninsula. Fgll,- Mean precipitation for the three fall months (September, October, and November) is illustrated in Figure 16. The most significant fact concerning the fall pattern is the change in location of the zones of heaviest precipitation. The northwestern Lower Peninsula (centered around East Jordan) and the northeastern Upper Peninsula, with over 9.5 inches of precipitation, are the wettest parts of the state during fall, in sharp contrast to spring and summer when they have average or below average precipitation. September contributes most to the high autumn rainfall in these zones, with many stations recording means of over 3.5 inches and some over 4 inches. No other part of the study area exceeds 4 inches during September or any of the other fall months.. In October precipitation averages decrease and regional dif- ferences are lessened. In November, however, the same sections that are rainiest in September are again significantly above the statewide average. November marks the beginning of the return to the winter pattern with precipitation decreasing over most of the state (notable exceptions are the northwestern Lower Peninsula, the northeastern Upper Peninsula, and the Keweenaw Peninsula). Minimum fall precipitation occurs in the eastern half of the Lower Peninsula, the interior of the western Upper Peninsula, and along the Keweenaw Peninsula-Lake Superior shoreline in the vicinity of Ontonagon. The latter area and the Lake St. Clair-Lake Erie shoreline, at the northwestern and southeastern extremities of the state, respectively, are the only sections with‘less than 7 inches 54 I I ' F I 1 MEAN SEPTEMBER PRECIPITATION MEAN OCTOBER PRECIPITATION “NON“ (IMO) l”! 1 lo“ ' I h. was 1..- I I“. v I a. a,” I I I I I MEAN NOVEMBER PRECIPITATION MEAN FALL pagcgprmnon (lwcwm (menu) "ECI'ITATION GREATER a o a: ‘8'" has as menu as as n "(OIMVA'ION L!” a so Yum I uncut! 6 so m man man can ‘0' I I“. ' I u. on Air 1 I... v 1 n .9" Figure 16 55 of precipitation during fall. Mean Frequency of Days with Precipitation ggual to or Greater than .10 Inch In addition to annual and monthly totals, frequency values of precipitation are valuable climatographic parameters. The threshold value selected for this analysis is .10 inch of precipitation per day (an arbitrary division between relatively light and moderate daily precipitation). The resultant pattern, shown in Figure 17, denotes a regional variation in values from 85 in the western Upper Peninsula to less than 65 in the vicinity of the Saginaw Lowland. In the Lower Peninsula the highest frequencies occur as cells in the western section but at least 20 miles from Lake Michigan. Values rarely exceed 80 days in the Lower Peninsula. The lowest frequencies are in the Saginaw Lowland, with an extension southeast- ward toward Detroit, although values increase slightly in this direction. Eastward from the 65-day isoline, values increase until they reach 75 along the shore of Lake Huron. In the Upper Peninsula the isolines trend parallel to the shore- lines of the adjacent Lakes with higher values generally occurring near the water bodies. The only exception is the Keweenaw Peninsula where the higher frequencies are found in the elevated parts of the Porcupine Mountains and the Copper Range. It is concluded that the combination of close proximity to a Great Lake and high elevation produces the maximum frequency of days with at least .10 inch of precipitation. Precipitation Variability Variability of annual precipitation in Michigan is shown in .IIIlI.I|III| ‘(nl'.‘ll IITIII‘II'I III IIII‘ 56 I I I MEAN NUMBER OF DAYS WITH PRECIPITATION EQUAL TO OR GREATER THAN .IO INCH O ‘0 [as J ls T E N, I963 Figure 17 57 Figure 18 by means of the coefficient of variation.1 The largest variations are in the extreme eastern section of the Lower Peninsula, in the vicinity of Mt. Clemens, Bay City, and Port Huron, with the latter station having the highest coefficient of variation (22.3%) for the study area. The least variability in the Lower Peninsula is in the northwest where Manistee (12%), Traverse City (13%), and East Jordan (11.6%) have only about one-half the variation of the south- eastern stations. Benton Harbor and Eau Claire in the southwest have above average coefficients as does the Cadillac-Fife Lake-Lake City triangle in the Northern Upland, although each is less than 20%. A small cell of below average variability (less than 14%) is centered around Newaygo and Big Rapids. It is the only area of relatively low variability in the southern Lower Peninsula. The Upper Peninsula has less precipitation variability than the Lower Peninsula. It is most variable in the west where a few coeffi- cients exceed 16% (Ontonagon 16.1 and Kenton 16.2). From Marquette eastward variabilities are less than 14% at every station, with the extreme eastern section having the most reliable precipitation of any part of the study area (Sault Ste. Marie 9.4% and Dunbar 8.8%). Comparison of the patterns for precipitation variabilities with precipitation totals (see Figure 12) yields no consistent relation- ships. High variabilities are associated with low precipitation (e.g., Saginaw Lowland) and they may be found in areas of high precipitation (e.g., southwestern Lower Peninsula). The same is true for low variabilities. On the basis of this analysis it cannot be assumed 1See footnote page 43. 58 I If I COEFFICIENT OF VARIATION FOR MEAN ANNUAL PRECIPITATION (PERCENTAGE) PERCENTAGE GREATER THAN IB PERCENTAGE LESS THAN I4 Ess- COEFFICIENT or: VARIATION- STANDARD DEVIATION/NEAN x IOO ° 50 MILES loo. 1 104' 'r. E N , uses Figure 18 59 that a significant correlation exists between mean annual precipi- tation and precipitation variability within the study area. Variabilities for individual months are, of course, without exception greater than for annual precipitation. A sample of 25 stations analyzed for the mid-season months indicates that January and April are the least variable, July is intermediate, and October is the most changeable from year to year. In January, the coeffi- cients vary from 31% to 64%, in April from 38% to 67%, and in both months the majority of stations average around 50%. In July, percentages range from 42 to 73, with most stations clustering be- tween 55% and 60%. In October, coefficients grade from 48% to 88% with a dispersal that makes difficult any determination of central tendency. Monthly precipitation variabilities at individual stations are generally consistent with the distribution of mean annual precipita- tion variabilities. For example, Benton Harbor has very high coefficients in every month except January when it is lower than average. It also has highly variable annual precipitation. East Jordan, on the other hand, with annual precipitation variability well below the statewide average, is characterized by low coefficients of variation for the mid-season months. The:1emporal Precipitation Regigg. The purpose of this section is to determine the temporal precipitation regime of the study area, or the periods of maximum and minimum precipitation. Because of the high variability of monthly rainfall from year to year (see previous section), the use of mean values to establish precipitation-regime types is not satisfactory 60 without further statistical refinement. The statistical method adapted1 involves elimination of the extreme quartiles, and estab- lishing single-month maxima only when the mean of the remaining 55%- fractile for the month with the greatest precipitation exceeds that of the preceeding and succeeding months by 20%. If the means of the 55%-fractile of any two months are within 20% of each other, a double- month maximum exists, providing both of these values are at least 20% higher than the amount received in the next highest month. Plotting the values for monthly means, and illustrating the results in Figure 19, the following regime types may be delimited for the Lower Peninsula: 1. Late Sprigg:Early Summer Maxiggg, This type is charact- erized by either a single-month maximum in May or a double-month maximum in May and June. Its areal occur- rence is south of a line connecting Benton Harbor, Lansing, and Port Huron, with a northern extension fringing Saginaw Bay. 2. Late Summer-Early Fall Maximum. The northern Lower Penin- sula has a marked single-month maximum in September or a double-month maximum in August and September. Toward the north, the single-month maximum is more typical while toward the south the double-month subtype dominates. The type is confined largely to the area north of Saginaw Bay, with the exceptions of a peninsular extension toward the 1This method was suggested by Dieter H. Brunnschweiler, "Precipitation Regime of the Lower Peninsula of Michigan," Papers of the Michigan Academy of Science, Arts, and Letters, Vol. XLVII, 1962, Pp. 367-381. 61 PRECIPITATION REGIMES Figure 19 types: The 62 south in the center of the state and a small outlier centered around Michigan. Transition Zone. The area between types 1 and 2 partakes of characteristics of both and, therefore, has extended peaks in May-June and August-September. The northern stations all have higher precipitation during fall than spring, while for the southern stations the reverse is true. Upper Peninsula may also be divided into three different Early Fall Maximum. This type has a marked singleqmonth maximum in September. It encompasses the entire eastern Upper Peninsula from Chatham and Fayette-Sack Bay eastward. In the extreme east, September maxima are very strongly marked, but, towards the west, June secondary maxima are also characteristic. It is comparable to the adjacent type 2 in the northern Lower Peninsula, except that in the Upper Peninsula September precipitation is always significantly higher than August precipitation. Early Summer Maximum. The area to the west of L'Anse and Stambaugh has a well-defined June maximum. A subtype occurs in the Reweenaw Peninsula where there is a June-January double-month maximum. This is the only part of the study area that has maximum precipitation during a winter month. The early-summer type is similar to type 1 in the Lower Peninsula, the principal difference being that in the Upper Peninsula the maxima are always in June and are very strongly marked. 63 3. Mid-Summer Maximum-Transitional. A north-south corridor from Ishpeming to Escanaba and thence southwest to Stephen- son and Iron Mountain lacks the well-defined maxima to the east and the west. Also, this type has either single~month maxima in July or August or double-month maxima involving both months. It is transitional between types 1 and 2 and its areal extent is much smaller. The majority of the investigated stations in both peninsulas record minimum precipitation in February (see footnote page 47). How- ever, in some of the more northerly Upper Peninsula stations the minima are delayed until March or April. Calumet and Houghton in the Keweenaw Peninsula subtype have well-defined March minima. The Grand Marais-Germfask area has double-month minima in March and April. A common characteristic of most Michigan stations is a mid- summer slump in precipitation.1 For all Lower Peninsula stations and many Upper Peninsula stations this is reflected in the July means, which are invariably lower than June or August averages. However, in the east-central Upper Peninsula the slump involves both July and August, with these months being significantly lower than June or September at Fayette-Sack Bay, Detour, Munising, and Grand Marais. At Marquette, July has less precipitation than June, but August is much drier than July or September. An anomaly in terms of temporal distribution is the narrow cor- ridor from Ishpeming south to Iron Mountain, Stephenson, and Escanaba. This is the only part of the study area that does not experience a 11bid., P. 379. 64 mid-summer decrease in rainfall; instead, it has its maximum pre- cipitation at this time. Ishpeming and Escanaba are unique in that they are the only stations recording July maxima. The explanation for the existence of this corridor may be sought in its transitional position between the June maxima to the west and the September maxima to the east. The Distribution_g£:Mean Annual Snowfall Snow is the most commonly occurring solid hydrometeor in the study area, although it exhibits great regional and temporal varia- bility. The period during which snow falls and remains on the ground varies somewhat from year to year, but, in general, it increases with higher latitude and higher elevation. During the sixsmonth span from November to April, snow may be expected at any station in Michigan. In the northern Lower Peninsula and the Upper Peninsula it is also fairly common in May and October. In many years no measurable snow- fall occurs at some stations during November and April; but the occasional very heavy falls during these months result in reasonably high averages in comparison to December, January, February, and March when measurable snow almost invariably occurs at all stations every year. The mean annual snowfall of the state is illustrated in Figure 20. Amounts range from over 160 inches in the western Upper Peninsula to less than 30 inches in the southeast near Detroit and Monroe, for a very high intraregional difference of over 130 inches. The Upper Peninsula clearly has greater average snowfall than the Lower Peninsula. The heaviest falls occur on the higher elevations 10 to 30 miles inland from the southern shores of Lake Superior. The snowfall 65 _c3- MEAN ANNUAL SNOWFALL UNCHES) MEAN SNOWFALL 50 - I 00 INCHES (LOWER PENI NSU LA ONLY) MEAN SNOWFALL OVER IOO INCHES MILES 150’ 84' Figure 20 TEN, I963 66 gradient from the Lake Superior shore towards the interior is very steep. For example, snowfall decreases from 160 inches at Ironwood to less than 60 inches at Stephenson within a distance of 145 miles. For the Lower Peninsula as a whole, there is a marked decrease in totals from the northwest to the southeast. Although the differ- ence between maximum and minimum (100 inches and 30 inches, approxi- mately) is not as great as in the Upper Peninsula, it is still appreciable. The Lower Peninsula has only a small area with over 100 inches of snowfall, situated on the western rim of the Northern Upland in the vicinity of East Jordan, Vanderbilt, and Fife Lake. This is also the area of steepest snowfall gradients in the southern peninsula. Snowbelts, or areas of exceptionally heavy snow accumulation, are a much discussed subject in the climatography of the Great Lakes region.1 In this analysis a snowbelt is defined as an area of significantly above-average snowfall for its latitudinal position and with a relatively steep gradient from the center to the edge of the belt. Five snowbelts may be delimited in Michigan. Three are in the Upper Peninsula: (1) the western rim of the Northern Highlands (Keweenaw Peninsula-Porcupine Mountains-Gogebic Range). It is well- defined and comprises the largest snowbelt with the highest average 1See, e.g., R. M. Dole, "Snow Squalls in the Lake Region," Monthly Weather Review, Vol. 56, No. 12, Dec. 1928, Pp. 512-513; C.L. Mitchell "Snow Flurries along the Eastern Shore of Lake Michigan," Monthly Weather Review, Vol. XLIX (1921), P. 502; J. T. Remick, "The Effect of Lake Erie on the Distribution of Precipitation in Winter," Bulletin American Meteorological Society, Vol. XXIII, Nos. 1 and 3, (1942), Pp. 1-4 and 111-117; and B. L. Wiggin, "Great Snows of the Great Lakes," Weatherwise, vol. 3, No. 6, Dec. 1950, Pp. 512-513. 67 snowfalls; (2) the Huron Mountains snowbelt; and (3) the Grand Marais- Munising-Newberry snowbelt which receives amounts intermediate between the two western areas. Two snowbelts are found in the Lower Peninsula: (1) the western rim of the Northern Upland between vanderbilt and Fife Lake is the larger, better-defined, and has the heavier snowfall of the two; and (2) the Ralemazoo-Bloomington-Allegan triangle. Although snowfall in the latter area is much less than in the other belts, the triangle stands out for its above average snow in southern Michigan. The variability of snowfall within the study area is somewhat greater than that for total precipitation. As determined by coeffi- cients of variation (see footnote page 43), the range of variabilities for annual snowfall is from 19% at Sault Ste. Marie to 40% at Detroit (compared to 9% and 22% for mean annual precipitation at the same stations). In general, stations in the northern part of the state have less variation than those in the southern part. There is no apparent relationship between close proximity to the shore of a Great Lake and low snowfall variability or greater distance from a Lake and high variability. Solid Precipitation Other Than Snowfall Solid precipitation other than snow, namely, hail, sleet, and freezing rain (or glaze) is relatively rare in the study area but 1 occurs with sufficient frequency to have noticeable climatic impact. Hail.- The primary significance of hail lies in its great 1Data for sleet are reported with those for snowfall. Separate data for hail and freezing rain are not included in the official statistics of the U.S. Weather Bureau. 68 destructiveness, particularly to crops. It is reaponsible for more property damage in the United States than sleet, freezing rain, or tornadoes, and, in some years, causes almost as much damage as hurricanes. During the period 1944 to 1953 only 15 hailstorms were recorded in Michigan, two of which were regarded as severe.1 All occurred in June, July, or August with the latter month accounting for 9 of the 15. If the state's record of 15 occurrences is compared with 559 in Montana and 440 in Kansas (allowing for differences in area) for the same period, it is evident that damaging hailstorms are rare events in Michigan. As far as regional distribution is concerned, the littoral sections of the state benefit from the stabilizing effects of the relatively cool water of the Great Lakes which inhibits the con- vection necessary to produce hail. Indicative of this stabilizing effect is the fact that the most severe hailstorms recorded in Michigan all occurred in the interior of the Lower Peninsula, at least 25 miles from the shore of a Great Lake.2 Hail normally occurs in association with severe thunderstorms. In the study area most thunderstorms take place in June, July, and August, although the other warm months usually experience a few. There is little regional difference in mean annual number of thunder- storms, with a range from 29 at Marquette and Alpena to 37 at Grand 1Snowden D. Flora, Hailstorms of the United States, (Norman, Okla.: Univ. of Oklahoma Press, 1956), P. 3. 2The most destructive hailstorm in Michigan's history was in Gratiot County (near Alma weather station) on August 1, 1953; an estimated $500,000 damage occurred at this time. See Flora, op. cit., Pp. 22-23. 69 Rapids. The average number is approximately 33 per year, with north- ern and Lake-shore stations recording slightly less than this number and stations in the south being slightly above the state's average. It is obvious that throughout Michigan only a very small proportion of thunderstorms are accompanied by damaging hail. Freezing Rain.- Freezing rain, or glaze, is not a form of pre- cipitation but is the accumulation of a coating of ice on surface objects. It occurs when supercooled rain or drizzle strikes a cold surface and immediately changes to ice. Glaze is not common because the values of meteorological variables must be within a very narrow range for the phenomenon to occur. The southern half of the Lower Peninsula averages as many glaze storms per year as any part of North America. The probability is high that a station in southern Michigan will experience one heavy glaze storm every three winters. In the northern Lower Peninsula one severe storm may be expected every 6 years. In the Upper Peninsula probabilities are high that more than 6 years will pass between two heavy freezing-rains.1 The distribution of glaze storms in Michigan in indicative of the fact that surface warm fronts do not normally reach the Upper Peninsula during the winter. Moisture-bearing air- masses are usually so far aloft before reaching the northern part of the state that any rain produced freezes (and becomes snow or sleet) before striking a cold surface. 1George H. T. Kimble, Our American Weather, (New York: McGraw- Hill, 1955), P. 16. 70 Moisture Elements Other Than Precipitation Humidit Relative humidity observations for Michigan's first-order weather stations are taken at 1:00 A.M., 7:00 A.M., 1:00 P.M., and 7:00 P.M.1 Regional differences do exist, but they are not large if comparisons are based on the same hour in the same month. Detroit, Marquette, Escanaba, and Alpena have relative humidity values some- what lower than Sault Ste. Marie, Muskegon, Flint, and Lansing. The highest average annual humidities are at Sault Ste. Marie which has 86% at 1:00 A.M., 86% at 7:00.A.M., 68% at 1:00 P.M., and 76% at 7:00 P.M. Detroit has the lowest mean relative humidity values with 77%, 79%, 59%, and 65%, resPectively, for the same hours.2 The western Upper Peninsula has slightly lower humidity than the eastern Upper Peninsula, whereas the eastern Lower Peninsula has somewhat lower moisture content in its atmOSphere than the western Lower Peninsula. The fact that Marquette and Escanaba have relative humidities reason- ably close to those of Detroit, while, at the same time, experiencing significantly lower temperatures, indicates that the northwestern part of the Upper Peninsula has lower absolute humidities than the other sections of the state. Cloudiness Seven first-order stations in Michigan report data for percentage 1Official data are available for relative humidity, but only for first-order weather stations. No data are available for absolute humidity, specific humidity, or other moisture indices. 2Michigan Weather Service, Climate of Michigan -By Stations, (In cooperation with U.S. Weather Bureau), Lansing, Mich., Feb. 1963. 71 of possible sunshine received and for mean number of cloudy, partly cloudy, and clear days.1 Examination of these data indicates that, in general, the northern and eastern Upper Peninsula is the cloudiest part of the state (i.e., has the lowest percentage of possible sun- shine), and the eastern and southeastern part of the Lower Peninsula is the least cloudy. All parts of the state, however, receive less than 55% of possible sunshine, and at least two-thirds of the days are cloudy or partly cloudy.2 Sault Ste. Marie has the lowest percentage of possible sun- shine (45), and Detroit has the highest (54). Of the other reporting stations, Marquette has 50%, Escanaba 53%, Alpena 51%, Grand Rapids 48%, and Lansing 52%.3 It is apparent from the cited figures that regional differences in the study area are relatively small with respect to the ratio of actual to possible sunshine. A common char- acteristic of the state as a whole is the very low value of the percentages in comparison with other regions of the country. Michigan is situated in one of the cloudiest sections of the United States, with only the Pacific Northwest, parts of the eastern Great Lakes, and northern New England equalling or exceeding its mean cloud cover. 1Cloudy, partly cloudy, and clear days are determined by the proportion of the sky that is covered by clouds. Sky cover is ex- pressed as a range of from zero for no clouds to ten for complete sky cover. The number of clear days is based on average cloudiness of 0-3 tenths; partly cloudy days on 4-7 tenths; and cloudy days on 8-10 tenths. See, e.g., U.S. Dept. of Commerce, Weather Bureau, Local Climatological Data, Washington, D.C. 2Michigan Weather Service, Climate of Michigan--By Stations, op, cit. 31bid. 72 More conspicuous than regional differences, however, are the seasonal variations in cloudiness. In winter, no station within the state records more than two-fifths the amount of sunshine it could potentially receive for its latitude, and at some Lake-shore stations (e.g., Muskegon, Sault Ste. Marie, and Marquette) the duration of sunny hours is diminished by as much as 80% of the potential amount. During summer, the percentage of sunlight hours lost by cloud cover is greatly decreased, with most Lower Peninsula stations receiving about 70% of the possible sunshine and Upper Peninsula stations about 65%. Stations near the Great Lakes average more sunshine hours than those inland. In spring and fall the ratios of actual to possible sunshine are intermediate between the low percentages of winter and the high percentages of summer. In the northern part of the state it is cloudier in the fall than in the spring, whereas the reverse is true in the southern part. Since, in the south, spring has more precipita- tion than fall, while fall is wetter than spring in the north, a positive correlation between cloudiness and precipitation may be inferred. However, there is no positive relationship between cloud- iness and mean summer and mean winter precipitation. Winter is the cloudiest season but has the least precipitation, while summer, the sunniest season, has the greatest amount of rainfall. In winter, Detroit and Escanaba are clearly favored by their locations on the lee side of the state with reapect to Lakes Superior and Michigan, as evidenced by their significantly higher percentages of sunshine than the stations situated adjacent to these water bodies. No data are available for cloudiness above the Lake surfaces, but 73 there is no doubt that, in early winter, minimum percentages of sun- shine would be recorded because of highly unstable conditions over the unfrozen water.l Lake-shore stations clearly exhibit a higher incidence of clouds in Nevember and December than in the later winter months when large surfaces of the water bodies are frozen and assume, meteorologically, continental quality. During summer the effect of the Lakes upon cloudiness is inverted. The relatively cool water tends to diminish convection, and the con- sequent increase in stability results in decreased cloud formation. Lake-shore stations record the highest percentages of possible sun- shine for any part of the state at this time. Analysis of mean number of cloudy, partly cloudy, and clear days (see footnote page 71) in the average year produces results similar to those for percentage of possible sunshine received. Escanaba has the fewest cloudy days per year (155), and most clear days (102), with the other 108 days being classified as partly cloudy. Sault Ste. Marie has the greatest number of cloudy days (207), and, with Flint, has the least number of clear days (65). Considering the entire study area, stations on the lee side with respect to Lakes Michigan and Superior have a lesser number of cloudy days and a greater number of clear days than the windward-side stations. Flint, a lee-side station, is the only anomaly in this pattern. The effect upon cloudiness caused by close proximity to the cloud-producing surface of Lake Michigan is exemplified by conditions at Muskegon, which has 192 cloudy days per year, or 12 more than 1DeveIOpment of fogs over the Lakes ("Lake smokes") is often observed where areas inland within a few miles from the shore are clear. 74 lee-side Detroit. Yet Muskegon has 81 clear days per year compared to 80 at Detroit. Alpena, with a lee-side location, but near Lake Huron, has only 164 cloudy days per year (28 less than Muskegon) and 82 clear days (about the same as Muskegon). Although every station in the state has more clear days during the warmer half of the year, at Muskegon the clear days are very strongly concentrated in the summer and early fall months. Nearly 75% of the sunny days at this windward-side station occur from May to October. Escanaba, however, has only 57% of its clear days during this period.1 22s 2 is considerably greater The frequency of days with dense fog near the Great Lakes than it is in the interior of the study area. Muskegon, for example, averages 25 days per year with dense fog, while Grand Rapids, only 30 miles from Lake Michigan, has 19. Lansing, approximately 85 miles from Lake Michigan, averages 12 days per year with dense fog. The highest frequencies are found at the eastern end of Lake Superior, as exemplified by Sault Ste. Marie with 47 days of dense fog annually. The lowest frequencies occur at high elevations in the Northern Highlands and Northern Uplands where averages are less than 5 days per year. Table 2 summarizes fog data for the first-order weather stations of Michigan. 1Michigan Weather Service, Climate of Michigan--By Stations, 02. Cite 2Dense fog is defined officially as any surface cloud that reduces visability to less than 50 yards. The Weather Bureau also recognizes thick fog, medium fog, and moderate fog, but official data are not published. 75 TABLE 2 MEAN NUMBER OF DAYS WITH DENSE FOG J F M A M J J A S 0 N D Total Alpena 1 1 2 2 2 2 1 1 2 3 2 el_. 20 Detroit 2 2 l l l * * 1 1 l 1 1 12 Escanaba l 1 2 2 2 l_I 1 2 2 2 2 l__ 19 Flint p;;_ 2 1 1 1 1 l 2 2 3 2 2 20 Grand Rppids 2 2 l 1 1 l 1 3 ,_lv 2 2 2__ 19 E. Lansing l 1 1 * l 1 1 l_‘ 2 1 l 1 12 h—Tb—d—fiw Marquette 1 1 l 2 2 3 3 1 l l 1 l l§__ Muskggon 2 2 2 2 3 2 _l, 3 l 3 2 2 25 Sault Ste. Marie 2 2 3 3 3 4 5 7 7 6 2 3 47 * Less than one day Winds and Tornadoes Surface Winds The surface winds of the study area are a part of the circum- polar westerly component of the general atmospheric circulation, and, therefore, are prevailingly from the west. Deviations in the pre- vailing pattern are caused by migratory pressure systems and local terrestrial factors. Figure 21 indicates mean annual prevailing winds for eight first- order weather stations. The majority of months at most stations are dominated by northwesterly, westerly, or southwesterly winds. Although easterly, southerly, and northerly winds occur frequently they are Ii, III 'III I}; a I’Ill III. I.,)III'I|1 III-IllnII: I III all! III Ill’llu.llv I 76 LS7. __43° 4: PREVAILING WIND DIRECTIONS PREVAILING WIND DIRECTIONS FOR YEAR. EACH CIRCLE EOUALS 4 MONTHS. (IN THIS EXAMPLE, PREVAILING WINDS ARE THE NORTHERLY B MONTHS, WESTERLY 4 MONTHS, AID SOUTHWESTERLY 2 MONTHS.) TORNADO ORIGIN AND SUBSEOUENT TRACK IIBSS-IDSS.) (IF TRACK IS NOT TOO SHORT o 20 so so so Ioo TO mmcnw I 1 WEATHER suntan, CLIMATE or ; MILES ' MICHIGAN-BY STATIONS, AND TORNADO OCCURRENCES IN THE UNITED sures 0 Iss- ‘ T.E.N., I964 153 D0 .2; , ”B 0 AND TORNADO TRACKS Wk (gag UL sTE. MARIE I'D. , , a £5:be w D \ ’ \» 1‘!§’Mmau d \e S \ or” . / LANsINo o i , ’ Z: / . 1% yr 9"" ’\ ‘ DATA: U. S., DEPT. OF COMMERCE. Figure 21 77 rarely the prevailing winds. In the southern part of the study area, the prevailing winds tend to be southwesterly (particularly in summer), while in the northern section they are generally northwesterly through- out the year. Sault Ste. Marie and Alpena are the only first-order stations with prevailing easterly winds for any months of the year. However, at the former easterlies are typical during winter and at the latter they occur during summer. The explanation for this pattern may be sought in the relative location of the two stations and the mechanics of the lake and land breeze. In winter, especially when anticyclonic control prevails to the north of the study area, winds are often from the cold land toward the warm water of Lake Superior; therefore, they are easterly at Sault Ste. Marie. In summer the winds are reversed and join the prevailing westerly flow. The relative location of Alpena with respect to land and water is opposite that of Sault Ste. Marie. Consequently, in early summer, breezes are often from the cool surface of Lake Huron onto the warm land surface, and, therefore, easterly at Alpena. Prevailing wind directions vary with the synoptic weather type and air mass that are present. Table 3 indicates the prevailing wind directions associated with air mass types at five Michigan stations. Listed are the prevailing wind direction (capital) and its relative frequency, and the combined frequency of winds from the dominant quadrant (direction spelled out). For example, at Detroit in January, with cA air masses present, westerly winds occur 30% of the time, and southwesterly, westerly, and northwesterly winds combined, 60% of the time. 78 TABLE 3 PREVAILING WIND DIRECTIONS ACCORDING TO AIR MASS TYPEl (PERCENTAGE) January CA cP NcP mP mT W- 30 SW- 18 S- 32 NE- 100 SW- 50 Detroit West- 60 West- 52 South- 59 - South- 100 W- 23 SW- 19 S- 25 NE- 33 W- 100 Grand Rapids West- 61 West- 50 South- 62 East- 66 - SW- 28 SW- 20 SW- 27 NE- 100 W- 100 Traverse City West- 58 West- 44 Sougp:y67 . - - NW- 36 NW- 31 S- 36 N- 100 W- 100 Escanaba West- 77 West- 45 South- 57 - - E- 32 E- 33 SW- 26 E- 50 W- 100 Sault Ste. Marie East- 44 East- 53 Soupp: 57 East- 75 - July cP mT mP N- 30 S- 37 N- 100 Detroit North- 51 South- 76 - I Calm- 19 s- 32 N- 100 Grand Rapids South- 38 South- 61_ - SW- 41 SW- 50 SW- 100 Traverse City Soggp- 76 Soptp- 96 - N- 21 S- 48 S- 50 Escanaba Noggh- 43 South- 88 South- 100 W- 30 E- 40 S- 50 Sault Ste. Marie West- 42 East- 85 South- 100 1Interpreted from U.S., Dept. Of Commerce, Weather Bureau, Daily Weather Map, Washington , D.C., 1958-1962. Note: Capital represents most frequently occurring wind; direction Spelled out represents combined frequency Of winds from the dominant quadrant. 79 The following generalizations may be made from Table 3: (1) CA air masses are normally associated with westerly, southwesterly, or northwesterly winds. Only at Sault Ste. Marie are winds typically from the east with cA air masses; (2) in January, winds associated with CF air masses behave similar to those with CA air masses. Again, Sault Ste. Marie is the only station with prevailingly easterly winds. In July, however, westerly winds occur with cP air at Sault Ste. Marie; (3) NcP air masses have a preponderance Of southerly winds at all stations; (4) mP air masses are most commonly associated with north- erly or northeasterly winds; and (5) mT air does not occur with sufficient frequency in January to permit valid inferences, but in July it is closely related to southerly winds, except at Sault Ste. Marie where easterly circulation dominates. The percentage of southerly winds associated with mm air masses generally increases northward. Wind Speeds in Michigan vary considerably according to the synaptic situation and local terrain conditions. In terms of mean monthly speed in miles per hour, however, there is little regional difference. Mean velocities vary from 7 to 13 miles per hour, with winter months having the higher wind Speeds. The greatest mean velocities occur at lee-shore stations or in flat terrain. The south- ern part of the state has slightly higher wind Speeds in winter than the northern section, while the Opposite is true in summer. The northern half Of the study area has a smaller range of differences between the mean wind velocities of winter and summer. Tornadoes (High Velocity Wind Systems) The highest wind speeds recorded in Michigan are associated 80 with the small and transient, but extremely intense, cyclone referred to as the tornado. During the period 1916-1958 the study area had 177 tornadoes occurring on 114 different days.1 For the same period Illinois had 301 tornadoes, Missouri 446, and Kansas 1,041. Kansas, which lies in the center Of the belt Of maximum tornado frequency for North America, had more than three times as many tornadoes as Michigan during the mentioned period. Figure 21 shows origins and tracks for all tornadoes observed in the study area during the six-year period 1953-1958. Most Of the storms that were actually observed occurred in the southern half of the Lower Peninsula. Only 6 were recorded in the Upper Peninsula. The northwestern section Of the Lower Peninsula, from Muskegon northward to Suttons Bay and inland to Cadillac, was also an area of minimal occurrence, with only one being Observed. TO the northeast Of the latter area, and particularly on the lee-side of the Northern Upland, tornado densities are nearly equal to those in the southern part of the state. It is probable that the stabilizing effect of Lake Michigan is the most important cause of the frequency decrease in the Muskegon-Suttons Bay-Cadillac area. The majority Of tornado tracks in Michigan are oriented from the southwest to the northeast. The highest tornado frequency falls in June with 52 having been Observed from 1916 to 1958. May ranks second with 46, and April, July, and August have from 16 to 19 occurrences. A tornado was Observed at some place in the state during every month except December in 1U.S., Dept. Of Commerce, Weather Bureau, Tornado Occurrences ip_the United States, Technical Paper No. 20, Washington, D.C., 1960. 81 at least 1 of the 42 years of this period, but October, November, January, and February recorded only 1 or 2 each.1 Effects of the Great Lakes on Climatic Elements ‘ From the preceding paragraphs it is clear that the Great Lakes are major modifying factors in the elemental patterns of Michigan's climate. The purpose of this section is to summarize the nature and magnitude of the modifications which these water bodies have on the climate Of the study area. The general nature Of the relationships between the Great Lakes and the land surface of Michigan is illustrated in Figure 22 and Table 4. Both portray seasonal changes in the effects Of Lake and land on the climate of the state. In summer, the relatively cold Lakes dampen convection by chilling the base layers Of air masses, and thereby decrease lapse rates and promote atmospheric stability. At this time Of year the Lakes Often have higher barometric pressure over their surfaces than is found over the adjacent land. The land surface, heating rapidly and intensely during the daylight hours, labilizes the air over it by forcing it to rise convectionally, Often with resultant precipitation. The difference in pressure between water and land results in the establishment of land and lake breezes, with on-shore flow of air during the day and Off-shore flow at night. The Lake breeze Often tranSports relatively cool air on-shore during the day, and thus reduces temperatures near the shores. This is particularly evident for daily maximum temperatures in summer which 11bid., P. 34. I.I [[.|I|.|IIII',IIII.I III I'll! II. I! IlllllllIIIl ‘Ill-I'lui I I'll 82 LOW PRESSURE HIGH PRESSURE PRESSURE SEASONAL MODIFICATIONS OF THE GREAT LAKES ON THE CLIMATE OF MICHIGAN SUMMER LOW PRESSURE Q~¥ HIGH PRESSUR WINTER T.E.N., I904 Figure 22 83 mucosa was HE amass uu>Oo cacao mo unsoas use was no onhu no unmanned basses: 2,332 MOOUGGHOH mom Hams ¥ 0 i O * ¥ when musoau mo unmasz use: meannesm oanamsom we swwunuouom Hammsoem hanueoz use: uO>O no .:oH. noaumuanaooum Ana: when no Humanz new: *‘k-k nowumuwnaooum hanucox use: mamunquHOhowun< O 0 ¥ ¥ 0 mqmunumOHohu 'k'k dOfiUOOPflOU 0 ¥ seams no ..h 00 ousumuoeaua saws shun mo wonasz new: k. s>oam no ..m Dom snoumuunaua saws when mo wonasz new: an a sususuomaua Shawna: hawmn ¥ * snoumuunauy asawxmz sauna - ILL- maxed new: usouu Communm young: unsusuonaus Agenda: use: ooswusm maxed pang unsuo anEum uoowwo Damian no .asuusss hunoseouw no unseen umuuo>w heave honosvouw no unseen owsuo>m o>Ons 51 zmuHmoHZ ho HHoue can men e.a ~ n.~ n «.ma om A.mm an o.~e no oedema ensue eon Nee ~.e o n.~ m m.mn on n.em as e.oe mm osoeooe a e a a a a a m a a x as Honoe as as eoz mo mue con man o.aL om m.m NH n.mn mN m.om Ne mousse ensue ooH man m.eN mm m.N Na L.mn NN m.Nm om uNouooe N e x a N a N e a e Noeoa as as moz mo Honouoo . . mSH . . w.~n . . N.H . . S.SHH noonouunooo mo .02 use: can Nee o.mN oN e.N N o.mw nNH manor .oom Danae cos men m.eN nN n.a N o.Nw NNN sensuous con man N.oN on N.o a N.oN wNN mono omuo>see con men o.eN me N.o N n.oN eon mousse ensue con man m.om as o o n.oo noN unouuoo N a N e a a N a kuoe as he mo mulls moanwucoo II o MADaue onH o HH «H «H o« a « sm a« H oH «mmmmmummmmm onH o HH «H «H ”mm a « «m m« H oH sHouuoa Huuoe mm: Hm: mos: Hm; Inmme am: «Hm HH. Ham. HHa cHu mmmum _ mnH o « s s «s o« oH wH n« oH «H «Humm‘.oum ”Hana mmH o « s s ms mmwi oH wH n« sH HH assumes» nnH o « s s «s (mm oH wH n« oH «H «uHo omuo>sue mnH o « s s «s sH oH wH mm. 0H «H mmmmmmlmmmmm mnH o « s s «s mH oH wH «« 0H «H “Hanson H 3 on. :0: and :3: :5 and cm: 0AM 3m Ed in *:Am awmmmmm H«oaH-wnaHv monHHh H< mug“. Mush—k5» OHM—Noam mo mflHOZMD§h1>mue an «H n a ms « «H o «H «n n «H 1mmmmmmlmmmmm an nH m a ms w «H o «H «m m «H ”Houumn Hmuoe mo: Hma muss Has am: am: «Hm HHm Ham]: HHu :Hu “uncuoo nnH o (mm. on mH « m o « «m « n« «Humm .oum uHmmm mnH o on on «H « m o « «m « n« unassumm \wnH c on a« wH « n o « «m « «« «HHo omsu>sue nnH o on on wH « m o « «m « n« immmummnmmmmm mnH c on on «H « n o H «n « s« “Homwmm Hsuoa lummmllrlmmmunllmmmmL Hm: mm: as: ulmmm HHm Hmm HHm cHa «mmm susaHuaoo -- HH uHm«uommmuu .aowuo«>o0 vuuunuuu 0:0 oucuauu> .uusuuummaUu coma unmouuaou 0 0:0 mm .x Houoz 0.«H 0.0H 0.0a 0.0 H.HH “0000 «.0 «.00 0.« 0.0 «.00 0.HH 0.0 0.00 0.0a «.0 0.00 «.0« «.« 0.00 «.0« 0000 . can: 040 0.00 quflw 0.« 0.00 «.0« 0.0 0.00 «.0« 0.0 0.00 0.0« 0.0 «.00 0.0« 3mm duo: n.o «.o 0.0 o.H o.H o.H« n.o «.o n.0H o.H o.H o.«H o.H aha, o.o« Hmm n.0H 0.00H 0.0a 0.0 «.00 0.0« 0.« 0.0 0.«« 0.0 0.«H 0.0« 0.« 0.0 0.«0 0000 «.0 n.0H 0.0H 0.0 0.0a 0.0H «.« «.0 0.0H H.0 0.0H 0.0« 0.0 «.0 0.0« «MW 0.« H.00 0.0 «.« 0.00 0.0 0.0 0.00 0.HH 0.0 m.H0 «.HH 0.0 «.0« 0.0H {mam 0.0 0.«0 0.0 «.0 0.«0 «.0« «.« N.H0 «.0H 0.0 «.«0 0.H« 0.0 0.00 0.0« can H.« 0.00 0.0H Mme «.0« 0.«« 0.0 H.0H 0.0« 0.« 0.0 «.«« 0.« «.0 0.00 000 0.« 0.00 «.0« H.0 «.00 «.H« «.0 0.00 0.0« «.0 «.00 «.0« 0.0 «.00 0.00 HA0 0.0 0.H0 «.mH H.m 0.«0 «.m« 0.0 0.00 0.0« «.0 0.«0 0.0« 0.0 0.0« 0.0« . «as 040 0.00 0.0H 0.« 0.00 H.H« 0.« «.«0 0.0« 0.« 0.00 0.0« 0.« 0qu ~"m« HAO «.« 0.« 0.«« 0.0 0.00 0 « 0.0 0.0H 0.«« 0.0 0.0a 0.0« 0.0 0.0a «.00 can 0 «0 x 0 «0 N 0 «m x 0 «0 x m «0 N manna .000 90:00 «sundown huge ouuo>¢ua 000000 0:090 ufiouuon Nuuzaun mumwa mu=e¢uz oHeHosz op nuaaHum m< monaun amaqzasm nz< .mmozaHmas .«.mo0 mzamz mmsaammmzma «a qudfi 116 «.H «.H «.« «J «A .33 H.« «.«« «.«« «.« 0.3 «.«« 12 «.««H «.3 «.« «.«« «.3 «.«.H. «.«HH «.3 «uIHHH can: «.« «.3 «.«« «.3 «.«« «.3 0.« «.«« «.3 «.« «.«« «.3 «.« «.«« «.«« m3 502 «.3 «.«« «.«« «.0 «.«« «.«« «.« «.3 «.3 «.«...«.«« H.3 «.«h «.«« «.3 Has .w.« «.3 «4.3 «.« u«w.H« «.3 «.« «.«« «.«« «.3 «.««H H.«« «.2 «.««H «H... JHHS H.« «.«« «.«« 3.« H.«« «.«« «.« «.3 «.3 «.«. «.«« H.3 «.« H.«« H.3 l0; IJII«« IJIII« 3n 1....le «« «.« «.3 «.«« «.« «.«« «.«« HIIH.« I..«.«..« «.«« «.« «.«« H.H.H .lnwm |.1l«« [«.«« «w«« «.« «.3 «.«« «.« «.«« «.«« «.« «.«« «.3 «.« «.«« H.«« «Ina II-Jllllul-IolF q o o o «[IolP o o o o o o o J «H «H «3 «««« «3 «C «H «3 «««s «3 «««3 «3 «H |.1.««.IJ|I|« «« I..|« «« «.3 «.«« «.«« H.« «.«« «43. «.« H.«« «.3 «.« «.«« «.3 H.«« «.« «.«3 «.mm «.« «.«« «.Hs «.« «.«« «.«« «.« H.H« H.«« «.« «.«« «.«« HHa «.« «.« «+3 «.« «.01 «.013 «.« «.« «.3 «.« «.« «.3 «.« «.« «.«« 1134 IJNlm I1ll« «« Jl« 3 «.« «.H« «.3 «.« «.3 «.3 «.« «.H« «.H« H.« «.«« «.0« Lflq « «m x m «« HH « «m x « «« HH « «m « «gun: .oum uuaom «panacea «ago oauo>¢us 000000 wanna uaouuoa kum< voscflucoo it «a ”4009 117 i H.H «.H «.H «.H «.« .025 «.« «.«« «.«« «.3 H.«« «.«« «.« «.«« «.«« «.« «.3H «33 «.3 «.«« «.H« IanH HHH com: 3.« «.«« «.3« «.3 H.«« «.3 «.3 «.«« «.«« 3.3 «.«H 3.: «.« «.«H «.3« :34 Cum: «.« 3.«« 3.3 «.« 3.«« «.3« «.« 3.3« «$3 «.3 «.«flIHJ3 «.3 «.«.HIIJIIH «« ..|H.__Ha.. |1«« «.«« «.3« «+3 «.«« «33 «J|« lql«1«.«lrJ.||« «« HH«« Ir«..1[«HI|1«|:« r:|.|«3rnl«.1l«H «.3« fig ...«.4«. «.«« H.3... «.3 «.P«1«.«« «.3 «4H« I...IILH «« «3 H.«H «43 «.«l «.« «.H« in I.....« Hl «« «.«« 3.« «.3 «.H« .IJI«H «.« 3.3 «.«. «3« «.3« «4m «.« «.«« Ila: «.H «.H «.3« «.« «.« «.3« «.H «.« «.«« «.« «.«H «.«« «.« «.« «.«« mm «.« «.« «.«« «.« «.« «.H« «.« «.« «.«« «.« «.« «.«« «.« «.« «.«« HH. «.« «.«« «.«« «.3 3.3« «.«« 3.3 «.«H «.««, «.3 3.3« 3.: H.3 «.«H «.3« Se «.« «.«« «.«« «.« «.« «.«« «.« «.«« «.H« «.3 «.«« «.«« «.« «.3 «.«« H.H. 3.3 «.«H «.«« «.« «.3H «.«« H.3 H.«H 3.«« 3.« 3.HH «.H« «.« «.«H «.3« «H3 « «m «H m «« x « «« HH « «« HH « «« x ««.««: .30 :30 2.33000 «3.3 0395.5. 000000 05.5 30.300 NHE. coaawucoo II «a H.348 118 H.3 «.« «.3 «.« «.« .««H« «.«. «.«« 3.33 «.« H.«« «.«3 3.« «.«« 3.«3 «.« «.«3 «.«3 «.« «.«« «.H« wmwm 3.« «.H3 «.«3 «.« «.33 «.«« «.« «.«« «.H« «.« «.«« H.«« «.« «.«« «.«« sum cum: ..«qm.«u«qmmaamqmm «.3 «.3« «.«mi «u« «.«« «.00 ««w «.3« «.«« «.ML «.«« «.H«: Hz: -.3...« .J|l« HH «3 ._.«_...« «.« «.«« H.« «.3« «.«« m.« 3.33 «.«« Jm.« «.«« ri..|}« 3 J03 « « «.«« «.«« H.« «”01 «.«« «.« «.«« «.«« «.3 «.«H «.«« H.« «.m» «.H« («0mm «.« «.3« «.«3 3.« 3.H3 «.«3 «.« «.«« H.«3 «.« «.«« 3.«3 «.« «.«« «.«3 [«mm 3.« «.« «.3« «.« «.HH «.3« H.« «.«« «.«« «.3 «.«« «.«« «.« «.HH «.«« «mm «.« «.«« «.03 «.« «.«« «.«3 «.« «.«« «.«3 «.« «.«« «.H« «.« «.«3 «.«« (mum «.« «.«3 «.H« «.« «.«3 «.«« 0.« 3.«3 «.«« H.« «.«« «.«« «.« «.«« «.H« .11430 «.« H.«3 «.«3 «.« «.33 «.«3 H.« H.«« «.H« 3.« «.H« «.3« «.« 3.«« «.«« .Hmm «.« «.«« «.«3 «.« «.«H «.«3 H.3 «.«H «.«3 «.« «.« «.«3 «.« «.« «.«3 HH3 H.« «.«« «.«3 «.« 3.«« «.H« «.« «.«3 3.«« «.« «.«« «.«« «.« «.«« «.«« «H3 m «m x « «m x « «m x m «m x « «m x OHM“: «flum Ufiflfim “Odd—flow” %Ufl0 0mHO>flHH QUHQGM— vflQHU UHOHUQQ Honouoo vuacfiuaoo In «a MAQoau «00 .vnm «eunuauua any «noauuouuv new: weaflwm>oum ou weavuooou .mqu unsoaHow as women «0.0.«nav «umwuonASu any ««.« «3«.- «««.- «««.- «««.- «««.- «««. «3«. H««. nonaoooo a s s s a a a s . ««.« «««.- H««.- ««H.- «m«.- 3mm.- «««. «3«. «««. noneseoz .1 «r t. i. «s. k. k. ««.H 3««.- «««.- H««. «H3.- «««.- 3«3. «««. «««. nonoooo a s s s s s s HH.H «H«.- «««.- 3««.- «««.- H««.- «««. «««. «3«. nooaoomuw a s s s s k s ««.H «««.- «««.- 3mm.- «««.- «««.- xmw«. «««. «mm. onmuo< s s s s s « «H.H ««H.- «««.- «HH. «mm.- «««.- «33. «««. «««. «Hem s a s s s s ««.H «««. «H«.- ««H. ««H.- H««.- ««3. «««. «««. one« a a s s s ««.H ««H. H««.- «««.- 3«H.- H««.- «««. H««. 3««. «mm s a a a s ««.H -me.- «««.- «««.- 33«.- «««.- «H3. 3««. H««. H««m0 s s a s a a ««.H «««.- «w«.- ««H.- «3«.- «««.- «mm. «««. «««. «one: s s a s s a s «H.H 3««.- «««.- «««.- -«3.- «««.- «3«. «««. «««. -«m«snooa a k s a s s s s ««.H H««.- «««.- .mmw.- «10.- H««.- «3«. «3«. H««. «unease s s s s s s s s II-um»« ««.3Hn ««.«Hn 3«.«Hn 3Hn «Hn «Ho ««.«.H«HH «««.Hm muAnufiu «00 .0nu «eunuauna «00 «coauoouuv wag: wnuaua>oum ou 0n00u000a .oan umouo "usesaom an momma «0.0.«.Hv nunauouASn one «««. ««3.- «««.- H««.- «H3.- «««.- «H«.- «««. «««. sensuous a s s a a a «H«. HH«.- 33H. «««.- «««. «««. H«3.- «««. «««. nossseoz a s a s a «««. «««. «««.- «3«.- «««.- «««.- ««H. «3«. «««. useouoo s s s s a «««. «««. «««. «H«.- mmH. «««. «««.- 3«3. «««. «mmmmmmmm a s a a a a a «««. «H«. ««3. «««. «««. «««. «««. «««. «««. Hummus a s s s s a a H«3. «H«. «««. «««.- - «««. ««H. «««.- «««. H««. .«3«« a a a a ««3. «H«. «mm. «««.- «H«. «««. 3««.- «3«. «0w. seen a a s a a s H««. ««3. «««. H««. 3«3. 3««. «3H.- «3«. ««3. «mm a a a a % «««. «3«. «««.- «««.- mm«. H««.- «3«. «««. «««. HH«m0 .1 an as. us. as. k. «««. «««.- «««.- «««.- H«H.- «««.- H««. H«3. H««. eons: s a a s a «««. ««H.- «««.- «««.- «««.- 3««.- «««.- «««. «««. \«mnmmmmm % a k s s 3««. 3««.- 33s.- 3««.- 3mm.- H««.- 3««.- 333. H««. «usssue s s s a s s a sum ««.3Hu \«w.«Hu 3«.«Hu 3Hn «Hu «Hn 3««.H«HH 3««.HHH mnAm A¢Hmamflmmua nnaomgflm nz< ZOHHoH0 A00 .0nm movnuwueq A00 “coauoouwv vows weaawm>uu0 ou 0:00u0000 .oxma unsoaaom no women «0.0.«sav «unauoooau one ««.« H««.- «H«. H««.- «««. «««. «««.- H««. «««. nosesooo a» k. k. k. .1 k. k. ««.« 333. «««. «««.. «««. «««. «««.- «««. «««. nooeseoz &. k. .4. .4. a. k. «s. k. ««.H «««.- -flw«. «««.- .- «««. .mw«s- -133«-‘ «««. -««mm« .1 .1 .4. .4 * k. ««.« ««H. «H«. HH«.- «««. «««. «mms- «««. «««s sons: 0. i a... as k. .1 .4. ««.« «3H.- «H«. 3««.- «««. «««. «««.- H««s «««. \«nssnson an «s. .1 k. . .4. an ««.« «««.- «««. «««.- «««.. H««. «H«.- «««. 3««. «use««« ¥ .4. i a. an .1 t. o«« ««.33n 3«.«Hu 3«.«Hn 3Hu «3w: «Ho 3««smwa 3««.-H-HH 0HAQ Am.m «z< .3353 .92.. Home < tom... «02505 :0 20:55.8”... 3:50: 5...: no zen-«manna m5 «3«3.-e: zo.wwmm0mm 201m w.._<:o_wmm Figure 23 156 m a... 2(7; ”4(aoauc zo_._.<>m:_w oz< .wo:..._.r<4 .wz<._ ._.JIPZOZ zW\AO>IC>V ZO_wwmewm 20mm w4<39mw¢ Figure 24 157 extreme west. Escanaba averages the largest negative residuals, with LlAnse and Kenton also having high values. It is notable that these stations are leeward of the highest land in the study area, and con- sequently might be expected to experience a rainshadow effect. In the Lower Peninsula there are three areas where regression consistently predicts too much or too little precipitation. The two areas that are underestimated (positive residuals) are (1) along the Lake Huron shore as represented by Port Huron, Harbor Beach, and Harrisville, and (2) the extreme south-central section, particularly in the vicinity of Hillsdale. The only area of consistently over- estflmated precipitation is the Saginaw Lowland. A comparison of the maps of residuals for winter precipitation and the map for mean winter precipitation (see Figure 13) reveals a general correspondence between the two. In the Upper Peninsula the areas for which calculated values are too low are also the areas of maximum winter precipitation, and the area of least winter pre- cipitation (west-central section) is roughly coincident with the belt of greatest overestimation. In the Lower Peninsula the correspondence is less consistent. However, the Saginaw Lowland is both an area of overprediction and minimal winter precipitation, and the extreme south is an area of positive residuals and above average winter precipitation. The one section of the state where these relationships do not hold true is the northern Lower Peninsula. The Lake Huron littoral, although an area of underestmmation, does not have above average rainfall, but its mean precipitation is greater than the area to the west. 158 §££$2§,- The residual patterns for the Spring months (March, April, and May) are characteristic of the transitional nature of the season. This is particularly evident in the Upper Peninsula. The March residuals do not differ greatly from those of winter, except for a pocket of positive residuals near Stephenson in the extreme south. By April, however, the positive residuals characteristic of the eastern Upper Peninsula in winter are found farther westward in the vicinity of Munising and Chatham. Negative residuals disappear from the map in the western Upper Peninsula and reappear in the eastern section, although they are of low value in April. By May the transition from winter to summer is nearly complete. High positive residuals now dominate the west, while average value neg- atives are in evidence over the eastern half of the Peninsula. In the Lower Peninsula regional groupings of residuals are better defined than they were in winter. The high positive residuals, or areas of underestimation, are now in the extreme south and along the Lake Huron littoral, while the remainder of the Peninsula is dominated by negative residuals, and its precipitation is thus less than the values calculated by regression. Comparison of the patterns of residuals from regression and mean spring precipitation (see Figure 14) again indicates a high degree of correspondence. In general, precipitation is least in the eastern and extreme northern Upper Peninsula, which are the areas of negative precipitation residuals in May. The western Upper Peninsula, which receives heavy May precipitation, is an area of high positive residuals in this month. In the Lower Peninsula, the area of maximum precipita- tion in the south corresponds to one of the two major zones of high 159 positive residuals, while the northern section, the area of lowest precipitation, is dominated by negative residuals. §gggg£,- The residual pattern established in May continues to characterize the summer with only slight differences. During June, precipitation over almost the entire Upper Peninsula is underpredicted, as evidenced by the solid block of positive residuals. Eagle Harbor, on the northern tip of the Keweenaw Peninsula is the only Upper Peninsula station with a positive residual in June, and this is only -.5. In July and August, however, this pattern changes, as negative residuals dominate the eastern Upper Peninsula while positive residuals remain in the west. The residual pattern for precipitation in the Lower Peninsula remains essentially as it was in.May, i.e. strongly positive in the south and strongly negative in the north. Two elements of the summer pattern differ slightly from the May situation. The highest negatives are now concentrated along the shores of northern Lake Michigan and northern Lake Huron, especially in June and July. Also, in July, and even more so in.August, cells of positive residuals deve10p in the center of the Peninsula where negative residuals were found earlier in the spring. These cells may represent the convectional centers of the state during these months of maximum thunderstorm activity. Comparison of the residual patterns for summer precipitation and the map of mean summer precipitation (see Figure 15) again reveals a close correspondence. The western Upper Peninsula, the area of highest summer precipitation in the state also has the highest positive residuals. The periphery of the eastern Upper Peninsula has below average summer precipitation, and during July and August is dominated by negative 160 residuals. In the Lower Peninsula the same general relationship between residual pattern and mean precipitation is found. The only major exception is the cell of above average precipitation around Grayling in the Northern Upland which is not indicated in the pattern of residuals. It might be inferred that this cell is the result of higher elevations found in the area, and that this is taken into account in the regression equations. The southern Lower Peninsula, which has high positive residuals, is the area of greatest mean.summer precipitation. The northern Lower Peninsula littoral, which is the area of lowest precipitation, is an area of negative residuals. £§;_,- The change in residual patterns between August and Septem- ber, the first month of fall, is the most drastic for any two con- secutive months. The eastern Upper Peninsula and the northern Lower Peninsula which are strongly negative in August become strongly positive in September. The western Upper Peninsula which is highly positive in August becomes negative in September. The August cell of high positive residuals over the south-central Lower Peninsula is replaced in September by a high-value negative cell. The only area that corresponds reasonably well to the August pattern is the extreme southern Lower Peninsula which is positive in both months. The October pattern of residuals does not differ greatly from September except for small, but not insignificant, details. In the Upper Peninsula the high positive residuals which are located in the extreme east during September migrate to the north-central area around Munising and Chatham. In the Lower Peninsula there are two slight 161 shifts that are of significance. In the northeastern extremity of the Peninsula, a wedge of negative residuals pushes southward into the position occupied by positive residuals in September. And, in October, there is reestablishment of the high positive residuals along the southern Lake Huron littoral (Port Huron-Harbor Beach). The November pattern of residuals resembles that of December very closely, differing only slightly in the orientation and magnitude of the isolines. The principal differences between November and October are (1) the reappearance of high positive residuals in the extreme western Upper Peninsula, and (2) the establishment of a meridional, as opposed to zonal, orientation of the positive and negative residuals in the Lower Peninsula, with the positive values dominating most of the western half and the negatives incorporating most of the eastern half. Comparison of the residual patterns for fall precipitation and the map of mean fall precipitation (see Figure 16) again shows close correspondence between areas of above average precipitation and high positive residuals, and areas of below average precipitation and negative residuals. In the Lower Peninsula, where there is almost perfect accordance between the residuals and mean precipitation values, both residual isolines and isohyets have a marked meridional orienta- tion. The only exceptions to the general agreement between patterns are (l) the Gogebic Range-Porcupine Mountains area where above average precipitation is not evidenced by high positive residuals (except in November), and (2) along the Lake Huron shore where high positive residuals are not associated with above average precipitation. However, 162 the latter area does have slightly greater precipitation than the area to the west. Conclusions It is evident that the residuals from regression for precipitation are distributed in concentrations of negative and positive values. Areas enclosed by positive isolines have a strong tendency to be areas of above average precipitation, while those enclosed by negative iso- lines are likely to receive below average precipitation.1 In all of the above analyses it was noted that residual patterns and mean seasonal precipitation correspond closely. The residuals, however, add the following information to the analysis of precipitation distribution: (1) they represent the variation that remains after the effects of distance from a Great Lake, latitude, and elevation have been removed by regression analysis (i.e. factors expressing the rela- tionship between precipitation and the terrestrial controls). Regression explained 63 per cent of the variation in April but only about 25 per cent in May and December; (2) the remaining variation is not attributable to the selected terrestrial factors, but must be accounted for by other climatic controls if precipitation bears a cause-and-effect 1To ascertain that each of these regions has statistically signifi- cant differences from adjacent regions, they should be subjected to analysis of covariance. Analysis of covariance allows the testing of a regional classification while, at the same time, considering the effect of the relationships between variables within the various regions. If the regional classification is significant the covariance analysis will result in an increase in explained variance for the dependent variable. A substitute procedure for analysis of covariance is to examine the residual patterns for all three months of a season, and if the pattern is similar in all, to make the plausible assumption that regional differences do exist in that season and are significant. See Thomas, op. cit,, P. 5. 163 relationship to other physical phenomena, as may be assumed; and (3) although the residuals do not inform us what these unknown factors are, their regional groupings do indicate that the factors are areally differentiated within the study area. In the search for the factors that cause the unexplained varia- tion in Michigan's precipitation, the following are suggested: 1. the location of the polar-front - this factor is one of the most important in the analysis of precipitation genesis, because its position determines, to a very large extent, the course of cyclonic storms and their associated rainfall. However, the polar front is usually oriented zonally, and, therefore, most of the variation in precipitation caused by its position, other than that which is locally induced, should be accounted for by latitude; 2. the tracks of synoptic weather systems - as indicated earlier, certain of the synoptic weather systems are responsible for most of the precipitation within the study area. It is possible that regional differences might occur because of position relative to the principal tracks of the major precipitation-inducing pressure centers, and this could account for some of the unexplained variation. Again, how- ever, most of these systems have mean trajectories from west-to-east, and their variations should, thus, be accounted for by latitude.. It was also shown in a preceding section that amounts of precipitation during specific synoptic situa- tions depend on location with respect to a Great Lake 164 (e.g. differences between lee-side stations such as Escanaba and Detroit, and windward-side stations as Grand Rapids, Traverse City, and Sault Ste. Marie). Therefore, some of the variation caused by synoptic influences should be explained by distance from a Great Lake; random disturbances - the occasional scattering of residuals, as opposed to their regional grouping, suggests that some of the unexplained variation in precipitation may be due to randomness. Some of the possible random disturbances are related to well-known physical causes such as locally varying degrees of convection. However, other scattering may occur by chance alone, and have no discernible physical basis; gggbined_e§fgcts of close proxflmity to a Great Lake_ggg steep elevation gradients - several of the areas in which precipitation was underestimated (positive residuals) are located at fairly high elevations on the windward side of the state relatively close to the water of a Great Lake. These are nearly always areas of above average precipitation. It is hereby postulated that the combined effects of high elevation and close proximity to a Great Lake result in heavier precipitation than predicted by the regression equations; location with respect to isthmuses - the precipitation pat- terns of the southern Lower Peninsula (particularly the southwestern portion) and the western Upper Peninsula, 165 although separated by several hundred miles of latitudinal distance, are markedly similar in both mean annual and seasonal precipitation. This is best exemplified by the patterns of increase during the spring when these two areas receive considerably more rainfall than the remainder of the state. For example, in May the western Upper Peninsula and the southern Lower Peninsula clearly have much higher precipitation than the eastern Upper Peninsula or northern Lower Peninsula. During summer (June, July, and August) this areal differentiation remains as definitive as in May. The southern Lower Peninsula and western Upper Peninsula obviously differ in terms of latitude and elevation, as well as location with respect to synaptic weather system trajectories. Although they are similar in terms of distance from a Great Lake, neither differs greatly from the northern Lower Peninsula or eastern Upper Peninsula in this respect. We may, therefore, postulate that the most significant physical factor in the similarity of precipitation patterns for these areas is their location adjacent to the southern extremities of the isthmuses connecting the Peninsulas to the continent. These land bridges, in both cases increasing in width toward the south, allow maritime trapical (m1) and modified continental polar (NcP) air masses to enter the southern Lower Peninsula and western Upper Peninsula without first passing over the surface of a Great Lake. In the fall when the northern Lower Peninsula and the eastern Upper Peninsula have higher precipitation totals than the western Upper Peninsula and the southern Lower Peninsula, the Lakes are relatively warm compared to the air passing over them, and, therefore, tend to promote instability. 166 In summary, it is evident that the northern Lower Peninsula and the eastern Upper Peninsula have the highest degree of Lake~control over their precipitation regimes of any sections of the study area. The southern Lower Peninsula and western Upper Peninsula, conversely, have the highest degree of land-control, particularly with respect to the entrance of mT and NcP air masses into the state. These differ- ences are fundamental to the analysis of regional precipitation variations. Residuals from Regression for Mean.Monthly Snowfall Residuals from regression for the six months during which snow normally falls in the study area are shown in Figure 25. In the inter- pretation of these residuals it should be noted that the percentage of variation explained by regression was considerably higher for snowfall than for precipitation (from 57 to 78 per cent as compared to 25 to 63 per cent). One of the outstanding features visible on these maps is the strong concentration of high positive residuals centered around Munising in the Upper Peninsula, extending to Ishpeming in the west and to Grand Marais in the east. The underestimated snowfall here may be explained by the prevailing northerly winds which bear moist, unstable air after crossing 200 males of the relatively warm surface of Lake Superior. Also, the configuration of the shoreline acts as a funnel concentrating moist air into the Munising area. In the western Upper Peninsula, from LFAnse to Kenton and Stambaugh, and thence curving toward Stephenson and Escanaba, lies a zone of con- sistently negative residuals (correSponding roughly to an area of high 167 e. no..- zax» 5.33..» 34393: o... no... 5:: «333 3393,. DC] 202%)wa 02( .mo:..._._.(.. .924 hJIPZOZ z¢w._w oz< Josh-.5“. .wv.<.._ ._.JIHZOZ zmum oz< .mo:h_euxezoz zoa mouoouomqu uncoawaewau manure a “ouoz 11. .s--~aa .am .Aamaa .nan=-saueuz “ence smzv .manwaoc< Heoaomwooom ou coauospouooH ..un .aomnoz .h xocam new conga .h woumaaz managed .owumaucumuu coo we on: one was money moses mo oooouowmao mo ceaonwuomoo s newH o no. aam.~ «w~.m «we.m sne.m awe.n sme.n no.a mm.n ma. a~.a .oma o smm.u «ne.n «cw.m «oo.e ane.n see.m so.a ««.H no. m~.a .>oz o as. an. cm. a». ea. «sa.~ «ma.n sas.n «oo.~ .uoo c an. an. es. on. sws.~ sm~.~ «mn.~ smm.~ .aom o o an. o amm.~ aan.~ «Ho.u «Hm.~ .m=< a ma. 0 am~.n amn.~ «mo.~ «mo.m .Hsh o ea. som.~ awn.~ aoe.~ sa~.~ .aas o amm.~ «on.N asn.~ tom.N mm: o Ne. so. am. .ua< o mm. HN. .umz o es. .asa O .cmh .oon .>oz .uoo qmum muw< .Hnfi .no& as: .un< .umz .oom .ooh mauuuhm ouommmum an“: Aoeaaunnmav zaoamoaz manages eszmam mace nz< maeHm so «warez mom amamma mzamz so mozmmmmmoa H mam<9 224 225 o no. sos.a ame.~ ses.~ sas.m sea.~ mm. an. an. eN. som.a .oua o am.a son.” san.a saa.m som.a on. an. so.o as. saa.~ .>oz o as. we. amh.a o mm. an.a som.~ sca.~ sno.m .nuo c an. Ne.a we. we. aw~.~ ans.m «ca.~ sea.m .aom o a~.a mm. as. *No.N «so.~ amo.u she.m .w=< o sam.n saw.n ass.m soa.e swo.e ank.s .nas c an. as.n sem.~ «on.~ som.m .css o oe. so.a Ho.a amm.a as: o a~.n oo.n sa~.~ .na< o o as.n .nmz o om.a .aum .omn .>oz .uuo «mmm vosdwuaoo In H qu