Because of its nearly 400 mile length and mid-continental situation, Illinois has a widely varying climate. Monthly average temperatures range from a high of 88 °F in the south during the month of August to a low of 10 °F in the northwest during February. Average yearly precipitation for Illinois varies from just over 48 inches at the southern tip to around 35 inches in the northern portion of the state. Normal annual snowfall exceeds 38 inches in Chicago, while the southern portion of the state normally receives less than 14 inches. The highest temperature recorded in Illinois was 117 °F, recorded on July 14, 1954, at East St. Louis, while the lowest temperature was -36 °F, recorded on January 5, 1999, at Congerville.
Illinois averages around 50 days of thunderstorm activity a year which put it at near average for number of thunderstorm days for the United States. Illinois is vulnerable to tornadoes with an average of 35 occurring annually, which puts much of the state at around 5 tornadoes per 10,000 square miles annually.