Climate of Glenwood, Illinois

Climate of Illinois

Illinois lies midway between the Continental Divide and the Atlantic Ocean and some 500 miles north of the Gulf of Mexico. Its climate is typically continental with cold winter, warm summers, and frequent short period fluctuations in temperature, humidity, cloudiness, and wind direction. The excellent soil and well distributed annual precipitation of 32 to 48 inches favor a very high standard of agricultural produc tion.

PHYSIOGRAPHY

Except for a few low hills in the extreme south and a small unglaciated area in the extreme northwest, the terrain is flat. Differences in elevation have no significant influence on the climate. River drainage is mainly toward the Mississippi River, which forms the entire western boundary of the State. Approximately one-seventh of the State area drains southeastward into the Wabash and Ohio Rivers. Only a small area drains into lake Michigan. The deep, loess soils of the central and northern portions were originally in prairie. Forests in the extreme south, and scattered areas of forest in the north, have long since been cut down, but reforestation is active in parts of the south.

CLIMATIC PATTERNS

Without the protection of natural barriers, such as mountain ranges, of natural barriers, Illinois experiences the full sweep of the winds which are constantly bringing in the climates of other areas. Southeast and easterly winds bring mild and wet weather; southerly winds are warm and showerly: westerly winds are warm and showerly: westerly winds are dry with moderate temperatures, and winds from the northwest and north are cool and dry. Winds are controlled by the storm systems and weather fronts which move eastward and northeastward through this area. Storm systems move through the State most frequently during the winter and spring months and cause a maximum of cloudiness during those seasons. Storm systems in the summer-season tend to be weaker and stay farther north, The sun in autumn is pleasant dry weather until the returning storminess which usually begins in November.

TEMPERATURE

The extreme north has frequent snows and temperatures drop to below zero several times each winter. The soil freezes to a depth of about 3 feet and remains snow-covered for weeks. During the summer season the sun heats the entire State quite strongly and uniformly. The north-south range of mean temperatures in July is about 6F. The annual average of days with temperatures of 90F or higher. Summer also brings periods of uncomfortably hot and humid weather, which are most persistent in the south. In the north the heat is usually broken after a few days by the arrival of cool air from Canada, but this cooling does not always penetrate to the southern portions of the State. The highest temperature of record is 117F observed July 14,1954, at East St. Louis:the lowest -35F., January 22, 1930, at Mount Carroll.

SNOWFALL

The annual average of snowfall ranges from near 30 inches in the extreme north to only 10 inches in the extreme south. Extreme north the most likely form of winter precipitation is snow. In a large number of winter storm situations, only a slight change in the temperature pattern would change rain to snow. Snow falls of 1 inch or more occur on an average of 10 to 12 days per year in the north.

SEVERE STORMS

Heavy snows of 4-6 inches or more average one or two per year in the north and less frequently in the south. Strong winds will drift snow and make driving hazardous. Major highways may become impassable for a time. Heavy storms come about once in four of five years and quite damaging to utility lines and trees, as well as being a serious traffic hazard. Thunderstorms average about 35 to 50 annually.

WEATHER AND PEOPLE

Illinois climate are adequate, but seldom excessive, rainfall and the lack of severe extremes. A similar climate prevails throughout the heavily populated and productive section of the United States which extends from the upper Mississippi Valley eastward to the middle Atlantic states.

INFLUENCE OF LAKE MICHIGAN

Because winds are westerly and storm systems move from the same direction, the influence of the lake on Illinois weather is not large.

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