GIFT OF i'wA It: I OUR CLIMATE !#? Useful Information regarding the Climate between the Rocky Mountains and the Atlantic Coast, with special reference to MARYLAND -AND- DELAWARE Prepared by JAMES H. SPENCER, Meteorologist BALTIMORE, MD. Issued by the MARYLAND STATE WEATHER SERVICE In cooperation with the UNITED STATES WEATHER BUREAU CHARLES F. MARVIN. Chief Board of Government, Maryland State Weather Service : Director, Prof. Edward B. Mathews, Johns Hopkins University, Baltimore, Md. ; Secretary and Treasurer, Prof. W. T. L. Taliaferro, University of Maryland, College Park, Md. ; Meteorologist, James H. Spencer, U. S. Weather Bureau, Baltimore, Md. TV /[ ARYLAND AND DELAWARE have an excellent corps of Cooperative + * * Observers, many of whom have been taking daily weather observations for the United States Weather Bureau and the Maryland State Weather Service for more than a quarter of a century. Except for the faithful work that these Cooperative Observers are doing, the publication of this Booklet would, of course, be impossible. In its preparation the records of about 65 stations in Maryland and Delaware have been used. The equipment of a Cooperative Observer consists of a maximum and a minimum ther- mometer, a thermometer shelter, and a rain gage. An intelligent idea of one's climate can best be obtained, per- haps, by comparing climatic data for the various sections of the country, and this is the reason why data are included in this Booklet for all sections of the United Slates east of the Rocky Mountains. Most of the information that relates to other States was fur- nished by Weather Bureau officials especially for this Booklet, but some COOPERATIVE OBSERVER'S EQUIPMENT of lhe averages tna t change only slightly from year to year were taken from Bulletin Q, published by the United States Weather Bureau Our thanks for valuable assistance in the preparation of this Booklet are due to Mr. Joseph Bily, Jr., Meteorologist, and to other members of the Weather Bureau force, at Baltimore, Md. ; also to Prof. Charles F. Marvin, Prof. Edward B. Mathews, and Prof. W. T. L. Taliaferro for many helpful suggestions. JAMES H. SPENCER, Meteorologist. Write to Local Office, V. S. Weather Bureau, Baltimore, Md , for Bulletins 94 and 9o. These Bulletins, published by the Weather Bureau, contain complete data for all cooperative weatherstations in Maryland and Delaware. Teachers may also obtain free of charge from the same source, :! beautiful Maryland State Weather Service Climatic Maps, printed in colors. 3 on i , OUR CLIMATE OUTSTANDING FEATURES We present in this Booklet some evidence that the Climate of Maryland and Delaware, when considered "all-the-year-round," is one of the best in the United States. Winters are mild, although characterized by weather that does not lack invigorating qualities. "Zero" weather has been recorded at Baltimore only 1 3 times in 50 years, and the lowest recorded during this 50-year period was 7 below zero. During a 20-year period "zero" weather was recorded only 5 times at Cambridge, 9 times at Easton, 12 times at Princess Anne, 15 times at Cheltenham, 32 times at Laurel, and 36 times at Frederick. Summers are warm, as in other good agricultural sections of the United States. They are, however, usually tempered by cool spells that originate in more northern latitudes, frequently in the Hudson Bay Region of Canada. Spring and Autumn are both delightful seasons. The geographic position of these States with reference to the usual storm paths is decidedly favorable for a uniform and abundant supply of moisture for all purposes. The annual precipitation averages 41.61 inches in Maryland and 43.25 inches in Delaware. The average annual snowfall is moderate, amounting to 2 7 inches, unmelted, in Maryland and Delaware. Snow does not remain long on the ground, as a rule. "Gloomy" weather is conspicuous by its absence. The sun shines at Baltimore during some portion of the day on about 32 1 days in the year, on the average. "Winter Sunshine" is nearly double the amount which occurs over a large portion of the Lower Lake Region. Yet days with 1 00 per cent, of sun- shine are rather rare at any season of the year, and a typical day is one on which the sky is partly covered with clouds. The "growing season," or frost-free period, is remarkably long for the latitude in which Maryland and Delaware are located, averaging about 185 days. There is little difference in the climate along the two shores of Chesapeake Bay, either as to temperature or precipitation. Severe storms are infrequent, prolonged droughts are of rare occurrence, and there is almost a total freedom from tornadoes. 4 MARYLAND AND DELAWARE 38.. lyn 15 3S .fc - .S N &-= - M 5-O G I - ="0 c .J.S 05 3*3*1 ' OUR CLIMATE THE LATEST FACTS ABOUT THE RAINFALL OF MARYLAND AND DELAWARE. The records of 69 cooperative stations in Maryland and Delaware show that the average annual precipitation for Maryland is 41.61 inches ; and for Delaware, 43.25 inches. The annual precipitation for the various sections of Maryland and Delaware is remarkably uniform and well-distributed through the year, and, except in St. Mary's County and the Cumberland Valley, falls between 40 and 47 inches. The maximum monthly amounts occur in August and the minimum monthly amounts occur in November. The average monthly amounts, in inches, for the two States as a whole, are shown in the following table : MONTH MD. DEL. MONTH MD. DEL. I any. . . . 3.28 3.26 July 4.30 453 Feby... . . 3.02 3.32 AUK . 4.43 456 March.... ....3.61 3.80 Sept .3.18 378 April ....3.37 3.43 Oct ,...2.96 1 19 Mav .. ..3.55 3.67 Nov... ..2.47 2.76 June 4.14 3.76 Dec 3.30 3.69 The ten stations having the longest records for the entire Maryland-Delaware section, together with the average annual amounts, in inches, are given in the following table : Annapolis 46.45 Fallston 46.90 Baltimore 43.18 Frederick 40.47 College Park 41.55 Woodstock College... 41 .98 Cumberland 34.87 Washington, D. C 43.50 Emmitsburg 44.24 Milford, Del 44.67 The average length of these 9 stations in Maryland and the District of Columbia is only slightly less than 50 years; and for Milford, Del., it is 38 years. Meteorologists and Agriculturists agree that in sections of the World without irrigation the annual precipitation should usually fall between 25 and 50 inches for the best results; and that precipitation must be well distributed through the crop season, as in Maryland. For further precipitation data, see pages 5,11, and 12. 6 MARYLAND AND DELAWARE OUR CLIMATE THE LATEST FACTS ABOUT THE TEMPERATURE OF MARYLAND AND DELAWARE. Except in the mountainous regions of Maryland, the general physical features of Maryland and Delaware are not favorable for great local climatic differences, but rather for uniformity in the prevailing weather conditions. Hence, it is not surprising that the differences in the average monthly temperatures for the various stations are small and fairly constant. East of the mountains, the range in annual temperature is from 52 in the extreme northern portion to 57 in the extreme southern. The average annual temperature for Maryland is 53.4 ; and for Delaware, 54.9. The average monthly temperatures, in degrees Fahrenheit, for the two States, are shown in the following table : MONTH MD. DEL. MONTH MD. DEL. Jany Feby 32.4 . .32.1 34.2 33.8 July Aug ..74.9 . 73.1 76.6 748 March . . April.... 41.9 52.1 42.7 52.7 Sept Oct .66.9 .56.2 68.4 578 Mav... ...62.7 63.6 Nov... ..44.2 46.0 June 70.2 71.6 Dec 34.3 36.5 The ten stations having the longest record for the entire Maryland -Delaware Section, together with the average annual temperature, in degrees Fahrenheit, are shown in the following table : Annapolis 55.7 Fallston 52.3 Baltimore 55.3 Frederick 53.8 College Park 54.1 Woodstock College 53.2 Cumberland 52.4 Washington, D. C 54.9 Emmitsburg 52.5 Milford, Del 55.9 For further temperature data, see pages 7, 13, 14, 15, and 1 6. MARYLAND AND DELAWARE II I! a II H "3 0-e OUR CLIMATE This Diagram shows HOW THE WIND YEAR I57o BLEW for a 11-year period at Baltimore, as recorded by a vane exposed 27.5 feet above the roof of the Custom House. Note that for the Year the most frequent direction was Southwest (18 per cent.), and the least frequent direction was East (6 per cent.). In WINTKK the most frequent direction was Southwest (20 per cent.) and the least frequent direction was East (5 per cent,). In SUMMER the most frequent direction was South (21 per cent.), and the least fre- quent direction was West (5 per cent.). In Summer, however, the wind blew South- west and South combined 39 percent, of the time. In Spring and Autumn there is a marked similarity in the percentages for the respective directions. This Diagram is computed from hourly directions. WINTER 16% SPRING 11% 18% 10 MARYLAND AND DELAWARE 3V ( 3 r GULF OF MEXICO # Less than 1 inch. In this Map the upper numbers for the various cities show the AVERAGE ANNUAL PRECIPITATION (in inches), and the numbers in parentheses show the AVERAGE ANNUAL UNMELTED SNOWFALL (in indies). For instance, at Baltimore the Average Annual Precipitation is 43 inches, and vhe Average Annual Unmelted Snowfall is 24 inches. By "Precipitation," we mean the amount of rain and melted snow. In MARYLAND and DELAWARE the Average Annual Precipitation (in inches) and the Average Annual Unmelted Snowfall (in inches) for a few selected cooperative weather stations are as follows: Annapolis, 46.4 and 23. College Park, 41.6 and 19. Easton, 40.7 and 16. Fallston, 46.9 and 26. Frederick, 40.5 and 27. Oakland, 45.7 and 69. Princess Anne, 41.8 and 1 4. Solomons, 36.5 and 1 8. Millsboro, Del., 44.4 and 1 7. Wilmington, Del, 44.4 and 23. 11 \ OUR CLIMATE 100 (136T 79 10 Q \ 126 \ ' V SHCtUfr KNOXVILIE \>J.<3l .X .V 208) (*207) > ^ 119 r ' [2201 118 MONT60MRy (246) 207) In this Map the upper numbers for the various cities show the ANNUAL NUMBER OF DAYS WITH .01 OF AN INCH OR MORE OF PRECIPITATION, and the numbers in parentheses show the NUMBER OF PAYS THAT INTERVENE BETWEEN THE AVERAGE. DATE .OF LATEST KILLING FROST IN SPRING AND THE AVERAGE DATE OF EARLIEST KILLING FROST IN AUTUMN. This period is commonly known as the "Growing Season." At Baltimore, for instance, 1 29 days in the year on the average give .01 of an inch or more of Precipitation, and the Average Lenglh of the Growing Season is 2 1 5 days. The Average Length of the Growing Season in Maryland as a whole is 1 85 days, though it varies for the various divisions of the State. See Map, page 9. 12 MARYLAND AND DELAWARE In this Map the upper numbers for the various cities show the ANNUAL MEAN TEMPERATURE (in degrees Fahrenheit), and the numbers in parentheses show the AVERAGE ANNUAL NUMBER OF DAYS WITH MAXIMUM TEMPERATURE 90 OR ABOVE. For instance, at Baltimore the Annual Mean Temperature is 55, and there is an average of 20 days in the year when the Maximum Temperature is 90 or above. In MARYLAND and DELAWARE the Annual Mean Temperature and the Average Annual Number of Days with Maximum Temperature 90 or above for a few selected cooperative weather stations are as follows : Annapolis, 56 and 22. College Park, 54 and 31. Easton, 55 and 14. Fallston, 52 and 10. Frederick, 54 and 31. Oakland, 47 and 2. Princess Anne, 56 and 10. Solomons, 57" and 23. Millsboro, Del., 55 and 26. Wilmington, Del, 54 V and 21. 13 OUR CLIMATE MAP SHOWING THE HIGHEST AND LOWEST TEMPER- ATURES OF RECORD, IN DEGREES FAHRENHEIT, FOR THE VARIOUS CITIES. At Cincinnati, Ohio, for instance, the highest temperature ever recorded is 1 05 and the lowest is 1 7 below zero, as shown on the map. At Baltimore 1 05 occurred on August 5, 1918, and 7 below zero occurred on February 10, 1 899 ; these are the highest and lowest temperatures at Baltimore in a 5 2 -year period, beginning in 1871. In MARYLAND and DELAWARE the highest and lowest temperatures ever recorded at a few selected cooperative stations are as follows : Annapolis, 106 and 6. College Park, 106 and 26. Easton, 101 and 15. Fallston, 103 and 14. Frederick, 104 and 2 I . Oakland, 101 and 40. Princess Anne, 99 and 1 . Solomons, 1 04 and 5 . Millsboro, Del., 1 06 and 17. Wilmington, Del., 1 7 and 1 2 . Highest temperatures were recorded in most cases on August 6 or 7, 1918. Lowest temperatures were recorded in most cases in February, 1899, or January, 1912. 14 MARYLAND AND DELAWARE 67 82. 5X1/V AHTON/0 (54) (55) GULF OF MEXICO In this Map the upper numbers for the various cities show the AVERAGE SUMMER TEMPERATURE, and the numbers in parentheses show the AVERAGE WINTER TEMPERATURE. For instance, at Baltimore the Average Summer Temperature is 76, and the Average Winter Temperature is 35. IN DEGREES FAHRENHEIT. In MARYLAND and DELAWARE the Average Summer Temperature and the Average Winter Temperature for a few selected cooperative weather stations are as follows: Annapolis, 76 and 35. College Park, 73 and 34. Easton, 74 and 35 . Fallston, 72 and 32 ". Frederick, 74 and 33 . Oakland, 65 and 28 ". Princess Anne, 74 and 38 . Solomons, 76 and 36 . Millsboro, Del., 74 and 35 . Wilmington, Del., 74 and 33. 15 OUR CLIMATE GULF OF MEXICO #Less than 1, In this Map the upper numbers for the various cities show the AVERAGE ANNUAL NUMBER OF DAYS WITH MINIMUM TEMPERATURE BELOW FREEZING, and the numbers in parentheses show the AVERAGE ANNUAL NUMBER OF DAYS WITH MINIMUM TEMPERATURE BELOW ZERO. For instance, at Baltimore the Average Annual Number of Days with Minimum Temperature below Freezing is 76, and the Average Annual Number of Days with Minimum Temperature below Zero is less than 1 . In MARYLAND and DELAWARE the Average Annual Number of Days with Minimum Temperature below Freezing and the Average Annual Number of Days with Minimum Temperature below Zero for a few selected co- operative weather stations are as follows : Annapolis, 85 and less than 1 . College Park, 120 and 2. Easton, 92 and less than 1. Fallston, 110 and 1. Frederick, 105 and 2. Oakland, 163 and 10. Princess Anne, 105 and less than 1. Solomons, 74 and less than 1. Millsboro, Del., I 03 and 1 . Wilmington, Del., 82 and 1 . 16 MARYLAND AND DELAWARE Apr. 1 S Oct 8 24 Goo/of c/ry Oct. 19 Aur 9 \ Apr. 1 .*&sc/A Oct. 1 Oct. 24^) 4BJ* Nov. 5 ST.iOU/S Apr. 4\ Oct. 29 Apr. 5 \\j uct. <;t> w/vMo/wl \/ Oct. 29 lU Apr v l^^ Mar. 1 Mar. J6 ^NoTlS Nov^l 5 ! ipr. 2 Apr. 3 r -v/)wi////A KNoyviue Oct. 27 Oct. 27 Man 31 Nov^e Mar. 10 MONTGOMERY Nov - n Feb. 16 'fer^? 1 Feb. NTON/0 Nov. 28 GULF OF MEXICO In this Map the upper dates for the various cities indicate the AVERAGE DATE OF LATEST KILLING FROST IN SPRING, and the lower dates indicate the AVERAGE DATE OF EARLIEST KILLING FROST IN AUTUMN. For instance, at Baltimore the Average Date of Latest Killing Frost in Spring is April 4, and the Average Date of Earliest Killing Frost in Autumn is November 5. In practically all sections of the United States the Average Date of Latest Killing Frost in Spring is a few days earlier in cities than in the surrounding country, and the Average Date of Earliest Killing Frost in Autumn is a few days later in the cities than in the surrounding country. That is, the Growing Season is slightly longer in cities than in rural districts. See the Maryland-Delaware Map, page 9, for additional frost data. 17 OUR CLIMATE In this Map the upper numbers for the various cities show the AVERAGE SUMMER RELATIVE HUMIDITY, and the numbers in parentheses show the AVERAGE SUMMER TEMPERATURE. For instance, at Baltimore the Relative Humidity in Summer averages 70^, and the Temperature in Summer averages 76. The Relative Humidity values given on this map are the mean of observations taken at 8 A. M. and 8 P. M., 75th Meridian Time, and are expressed as a percentage. The Average Summer Temperatures, which are the numbers in parentheses, are in degrees Fahrenheit. The most uncomfortable periods of Summer occur, as a rule, when both the Temperature and the Relative Humidity are high. 18 MARYLAND AND DELAWARE "WEATHER SIGNS" IN MARYLAND AND DELAWARE. SOME FACTS ABOUT THE WEATHER OF VALUE TO MOTOR-BOATMEN, AUTOMOBILISTS, FARMERS, AVIATORS, AND OTHERS. A typical day in Maryland and Delaware is one on which partly cloudy skies prevail, and hence there is almost always an excellent opportunity of studying the clouds. The most frequent fair weather clouds are Cumulus, which have flat bases and rounded tops, and which are illustrated in the first cloud photograph. They start to form in the morning of a bright day, grow larger and larger until after the warmest part of the day is past, then decrease in size, and disappear as a rule late in the afternoon. The highest of all clouds are called Cirrus. They are composed of ice specks that form in the very cold atmosphere 6 or 7 miles above the earth's surface. They always look very thin, white, feathery, and isolated. Cirrus clouds are not good "storm signals" as a rule, and they appear in nearly all kinds of weather. The "tufted" Cirrus is shown in the second cloud photograph. It is, however, an excellent indication of a coming storm when the sky becomes overcast wiih a very thin, whitish veil through which the sun shines brightly, provided this whitish veil thickens into a greyish veil within an hour or two, or more. The sun will be scarcely visible through the greyish veil, and there usually will be ram or snow within about 6 or 8 hours after these veil-like clouds over- spread the sky. The greyish veil is a lower cloud than the white veil, and between the elevations at which these two types form there are often to be seen clouds of great beauty Mackerel Sky, for instance. High, thin clouds nearly always move eastwardly very rapidly, though they seem to move slowly, just as an airplane does when very high in the air. WHAT CLOUD MOVEMENTS INDICATE. One of the chief benefits to be derived from watching the lower clouds is by observing the direction toward which they travel They are thick, and their direction changes like the wind. If they are moving from an easterly direction they indicate stormy weather in Maryland and Delaware, but if they are advancing from a westerly direction clearing weather is usually near at hand. 19 OUR CLIMATE _0 I e . I'l is, II il 20 MARYLAND AND DELAWARE .22 ^ H-O LS 03 21 OUR CLIMATE The local storms of Summer, however, come from a westerly direction, and when thunderheads, illustrated in the fourth cloud photograph, appear in the western sky on a hot, sultry day, they are an excellent sign of approaching rain. Hence, the saying "When clouds appear like hills and towers, The earth's refreshed by frequent showers." Rings around the sun or moon, or halos and coronas, are rather poor indicators of coming weather changes, and they chiefly show that between you and the sun or moon there are thin, icy clouds. WHAT THE BAROMETER INDICATES. If the barometer falls on a hot, sultry day, the winds usually being south or southeast, expect a thunderstorm in the afternoon. If the barometer begins to fall and the wind shifts from north to northeast expect cloudy weather, increasing northeast winds, and rain or snow within 12 hours. If a northeast storm sets in it will often last from 24 to 36 hours. A slowly falling barometer, with a brisk southwest wind, usually indicates clearing weather, although it may also bring a west or northwest blow. When the barometer starts to rise rapidly with a southwest wind, the wind will quickly change to west and northwest. Normal barometer is about 30.00 inches at sea-level. A "high" barometer in Summer is about 30.25 to 30.50 inches, and in Winter about 30.50 to 30.75 inches, or higher. High barometer indicates fair weather, unless the wind shifts to noriheast or east. A "low" barometer in Summer is about 29.75 to 29.50 inches, and in Winter about 29.50 to 29.25 inches, or lower. Unsettled weather will usually continue as long as the barometer remains low. HOW TO LOCATE THE STORM'S CENTER. The first thing that a weather forecaster wishes to know is where a storm's center is located. By "storm center" we mean the center of a low pressure area that chiefly controls the weather at any particular time. The winds usually give us this information with some degree of accuracy, when a weather map can not be consulted. This is the rule : Face the wind, and the center of the low pressure area will he off to one's right. 22 MARYLAND AND DELAWARE OUR CLIMATE For instance, in Maryland and Delaware : A southerly wind usually means that a storm's center is off to the westward, and that temperature above normal will continue. A southwest wind usually means that a storm's center is passing east- wardly over the Lake Region, and that sunshiny weather is in prospect. A northeast wind usually means that the barometer has risen considerably on or near the North Atlantic Coast, and it may also mean that a storm area is coming up the Atlantic Coast, from the Southwest ; this is the condition most favorable for stormy weather. A north wind usually means that we are passing out from under the influence of a storm area that has reached the North Atlantic Coast, and that fine weather will prevail. Light, variable winds usually mean that there will be little change in prevailing weather. The most important winds in Maryland and Delaware are northeast, south, southwest, and northwest. The other winds are usually of short duration. An unfavorable weather sign is a backing wind that is, a wind that passes from south to northwest, through the southeast, east, northeast, and north ; this is the long and stormy way round. A shifting wind, on the other hand, is always a good sign that is, a wind that passes from south to northwest through the southwest and west; this is the short way round, and usually means a quick clearing up. James H. Spencer, in the Baltimore Sunday Sun. MARYLAND AND DELAWARE 22 r ^of ! sl & 55 2.s 25 OUR CLIMATE HOW STORM TRACTS AFFECT THE WEATHER IN MARYLAND. The winds move in great whirls that travel in endless procession across the United States from the Pacific to the Atlantic. They may be likened to eddies in a river that are carried downstream by the current. These "wind whirls," which occur only in the lower region of the atmosphere, are carried across the country by contact with the swift upper currents of air that are ever moving eastwardly across the United States. The winds that bring us the stormy weather whirl spirally inward, as shown in diagram No. 1 . These whirls, commonly called Lows, may be 1 ,000 miles or more in diameter, but they vary greatly in size and shape. They reach the Pacific Coast from the North Pacific Ocean, and we locate them first on the weather map in Oregon, Washington, or farther north. They travel across the United States CANADA MEDICIME HAT DENVER MEMPHIS Diagram No. 1 A low-pressure whirl, or storm area, moving across the United States by the northern route Note that the winds blow spirally inward The broken arrow shows the approximate path of the storm. Whirls of this character bring the stormy weather to the regions over which they pass They often travel from the North Pacific Ocean* to the North Atlantic Ocean within a week. Following these whirls are the fair weather areas, with winds blowing outwardly. at about the average speed of an express train, but the movement is much faster in Winter than in Summer. All the important whirls' do not come from the Pacific, but the majority of them do. 26 MARYLAND AND DELAWARE The Lows, or storm areas, that chiefly affect the weather and climate of Maryland move across the country by one of three storm paths that are fairly well denned. One path is along the Canadian border; another is over Colorado, Kansas, Missouri, the Ohio Valley, and New England or the St. Lawrence Valley ; and the third is over Utah, New Mexico, the Gulf States, and thence noitheast- wardly near the Atlantic Coast. These storm paths are indicated by the arrows in diagram No. 2. THREE PRINCIPAL PATHS. Thus, we find that two of the three principal storm paths across the United States pass to the northward of Maryland, and this, perhaps, is the chief reason why this State has a climate that is characterized by an abundance of sunshine, a mild Winter, and an unusually long "growing season." Naturally you will ask, "What particular difference can it make in the weather and climate of Maryland whether the center of a storm area reaches the Atlantic by a path passing to the southward or to the northward of Maryland ?" The answer to this question may be stated thus: If a storm area passes to the southward of Maryland the winds over this section must back through the southeast, east, northeast, north, and northwest, and that is the long and stormy way round. Furthermore, this section will be in the colder, or northern, quadrant of the disturbance, where the air will be drawn down from Canada. On the other hand, if a storm area passes to the northward of Maryland the winds over this section must shift through the southwest, west, and northwest, and that means a quick change to clearing weather. It is a safe wager that on any day in Maryland when the wind is changing from south to northwest (through the southwest and west) we will have partial or full sunshine. Moreover, when the disturbance is passing to the northward of Maryland this section will be in the warm, or southern, quadrant, where the air will be drawn northward from the Sunny South. It will be noticed on diagram No. 2 that the storm areas that travel the middle route are deflected northeastwardly after reaching the Lower Ohio Valley. The Appalachian Mountains are probably responsible for this deflection, although the moist Lake Region may be another factor, since the "fuel" of the storm area is water vapor. The storm areas that travel the southern route are usually deflected northeastwardly by high pressure, or heavy air, over the Atlantic Ocean as they approach the Atlantic Coast. In other words, these disturbances always travel the path of least resistence. 27 OUR CLIMATE THE CAUSE OF FAIR WEATHER Areas with winds that whirl spirally outward also cross the country with great frequency. These are the high-pressure areas, or Highs, that bring fair, cool, and settled weather to Maryland. A great number of them travel all the way across the country, with the North Pacific Coast as the starting point. A considerable number also drop down from Canada some from the Medicine Hat Region north of Montana and the Dakotas, and others from the Hudson Bay Region. Most MEDICINE CANADA N^^ ^ v^/^ % %> CHICAGO ++* . \ DENVER ^ BALT J^ MEXICO N Diagram No. 2 Most of the storm areas that affect the weather of Maryland travel across the United States by routes indicated by the arrows in this diagram. Storm areas that passover the southern route cause the greater portion of Maryland's precipitation in Fall, Winter, and Spring, and they are known as "northeasters" because the wind blows Irom the northeast while the storm area is approaching from the Southwest Storm areas that travel the two northern routes cause only brief periods of stormy weather, or none at all ; they cause a shift in the wind from S. to NW., through SW. and W. of them, except those from the Hudson Bay Region, reach the Atlantic Coast via paths lying to the southward of Maryland, and as soon as they settle over the South Atlantic States, as most of them do, the temperature begins to rise in Maryland, the weather remaining fair. Suppose that Nature had reversed the conditions under which these areas of low and of high pressure reach the Atlantic, most of the Lows passing to the south of Maryland and most of the Highs passing to the north of Maryland. Under such conditions there would have been an excess of north and northeast winds and cold, stormy weather in this section, instead of the pleasant weather and moderate temperature that are actually enjoyed in Maryland most of the time. James H. Spencer, in the Baltimore Sunday Sun. 28 CONTENTS PAGES Barometer, meaning of changes in 22 Clouds, Alto-Cumulus, photograph '. 23 Cumulo-Nimbus, photograph 25 Cumulus, photograph 20 tufted Cirrus, photograph 21 what they indicate 19 Frost, average date of earliest killing in Autumn, at selected stations 17 average date of latest killing in Spring, at selected stations 17 Growing Season, length of, in Maryland and Delaware and at selected stations.. 12 Highs, or High-Pressure Areas, what they bring 28 Humidity, relative, average Summer, at selected stations 18 Ivow Pressure Whirl, diagram of 26 Ivows, or L,ow-Pressure Areas, what they bring 26, 27 Outstanding Features 4 Precipitation, annual nutnberof days with .01 inch or more, at selected stations.. 12 average annual, at selected stations 11 average annual, by States 5 Maryland and Delaware, annual and monthly 6 Maryland and Delaware, average annual, chart 5 Seasons, the, in Maryland and Delaware, character of 4 Snowfall, average annual, at selected stations 11 Storm's Center, how to locate.. 22 Storm Tracks, how they affect the weather in Maryland 26, 27, 28 Temperature, annual mean, at selected stations 13 aveiage annual, by States 7 average annual number of days with maximum 90 or above, at selected stations 13 average annual number of days with minimum below freezing, at selected stations 16 average annual number of days with minimum below zero, at selected stations 16 average Summer and average Winter, at selected stations 15 average Summer, at selected stations 18 highest and lowest of record, at selected stations 14 Maryland and Delaware, average annual , chart 7 Maryland and Delaware, average date of last freezing in Spring, and average date of first freezing in Autumn, chart 9 Maryland and Delaware, average monthly and annual 8 Tracks of Storm Areas, chart 28 Weather Signs in Maryland and Delaware 19 Wind, prevailing direction of, at Baltimore 10 Winds, changes in, and their meaning 24 Winter Sunshine 4 29 LOAN OEPT Photomount Pamphlet Binder Gaylord Bros. Makers Syracuse, N. Y. PAT. JAN 21, 1903 oi UNIVERSITY OF CALIFORNIA LIBRARY