Dear Tom,
Why does it seem that heavy snowfalls are frequently followed by very cold weather?
Mike Tabbert, Cary, Ill.
Dear Mike,
Chicago’s large snowfalls are generally caused by intense low pressure systems, that draw in warm moist air ahead of them, and cold dry air behind them as they depart.
Once the low pressure system passes and the snow ends, the strong and gusty winds shift northwest funneling cold arctic air into the city. The cold air is further chilled as it travels across the freshly snow-covered ground.
As skies clear and winds diminish, overnight temperatures plunge as the highly reflective snow surface radiates heat back into space.
Normally, the lowest temperatures will occur on the second or third night after a major snowfall.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
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