Back in 1959-60 when I was a student at North Park University in Chicago, there was a snowstorm when I heard thunder. How rare is it?
–Ken Carlson, New Berlin, Wis.
Thundersnow is a relatively rare event in Chicago, but it does occur during powerful winter storms. Snowfall can be intense when accompanied by thunder, falling at blinding intensities with accumulations up to 4 inches an hour. Several episodes of thunder and lightning occurred during Chicago’s 2011 Ground Hog Day blizzard, and on Dec. 15, 1987, the city was buried by 8 inches of snow in just four hours during a major thundersnow event. Thundersnow can also occur during lake-effect snow events, resulting from the extreme instability caused by arctic air passing over the Great Lakes’ warmer waters.