Illinois winters bring varying amounts of snow across the state. Understanding Illinois’s snowy season involves examining overall averages, regional distinctions, and the atmospheric conditions that contribute to these variations.
Statewide Snowfall Averages
The average annual snowfall for Illinois generally falls within a broad spectrum, often reported to be around 20 to 30 inches. This figure represents a statewide mean, but actual snowfall amounts differ significantly by location. For example, the central part of the state, around areas like Normal, sees an average of about 20 inches. This statewide average provides a general idea, but does not fully capture the distinct winter conditions from the northern border to the southern tip.
Regional Differences Across Illinois
Snowfall totals in Illinois exhibit a noticeable gradient, with northern regions typically receiving more snow. Northern Illinois, including the Chicago metropolitan area, generally experiences higher snowfall, often exceeding 30 inches annually. Chicago’s O’Hare International Airport, for example, averages 37.9 inches per year, and Rockford sees averages around 37.2 inches.
Moving south into Central Illinois, snowfall tends to decrease. Peoria reports an average of 37.6 inches, and Springfield averages 21.8 inches annually. Further south, snowfall diminishes considerably, with Southern Illinois receiving the least amount. Areas in extreme southern Illinois can average less than 10 to 14 inches annually. Carbondale, for instance, averages about 49 inches of total precipitation, but much of that is rain, with significantly lower snowfall.
Factors Influencing Illinois Snowfall
Several meteorological and geographical factors contribute to the varied snowfall amounts across Illinois. Latitude plays a role, as northern parts of the state are closer to colder air masses and storm tracks. This means temperatures are generally colder and stay below freezing longer in Northern Illinois. The polar jet stream often positions itself over or near Illinois, directing low-pressure systems that bring clouds, wind, and precipitation.
Lake Michigan also has a notable influence on snowfall, particularly in northeastern Illinois. This lake-effect snow occurs when cold air masses move across the relatively warmer lake waters. The warmer water heats the air above it, causing moisture-rich air to rise and form clouds that release heavy snowfall upon reaching land. Topography also plays a minor role; the Shawnee Hills in southern Illinois can increase annual precipitation, though this often manifests as rain due to warmer temperatures.
Record-Breaking Snowfall Events
Illinois has experienced several significant snowfall events throughout its recorded history. The snowiest winter on record for the entire state occurred in 1978-1979, with a statewide average of 44.5 inches of snow. Another notable winter was 1977-1978, which saw 44.4 inches statewide.
Individual storms have also left their mark. Chicago’s largest single snowstorm on record was the blizzard of January 26-27, 1967, which dumped 23 inches on the city. The Groundhog Day blizzard of 2011 also brought substantial snowfall, with Chicago’s O’Hare International Airport recording 21.2 inches, and some suburban areas seeing up to 27 inches. The greatest 24-hour snowfall recorded at Astoria was 37.8 inches on February 27-28, 1900.