Conditions earlier this week were exactly right for Lake Michigan to help the latest intense snowstorm drop up to 2 feet of snow in the Chicago area, according to David Kristovich, head of the Center for Atmospheric Science at the Illinois State Water Survey (ISWS).

Cold air blowing across a warmer lake and strong winds produce conditions ripe for heavy snows.  Exactly how the lake can enhance snows from low-pressure systems isn’t well known, but studies at the ISWS have provided some answers to why coastal areas often receive more snow during storms than areas farther inland.

“As the low-pressure system crossed over the lake, the lake’s warmer temperatures contributed heat and moisture to the atmosphere,” Kristovich said.  “The heat caused instability and the resulting updrafts allowed the extra moisture to condense into low clouds.  Snow from the deeper low-pressure system clouds fell into the low clouds, which caused rapid snow growth as it fell to earth in the form of snow.”

In this storm, the center of the low-pressure system moved across southern Illinois, bringing northeast winds to the Chicago area.  Even as the storm departed, a lake-effect snow band moved southeast through the Chicago area, adding to the snow from the storm.

As a result, snowfall in many locations within about 25 miles of the lake received 20 to 24 inches of snowfall, while areas in the outskirts of the city received generally lesser amounts of 12 to 15 inches, according to the National Oceanic and Atmospheric Administration.

Researchers have found that lake-effect snow typically affects areas within 10 to 30 miles downwind of the lake.

The Illinois State Water Survey at the University of Illinois at Urbana-Champaign, a division of the Institute of Natural Resource Sustainability, is the primary agency in Illinois concerned with water and atmospheric resources.