Dear Tom,
Why does it seem that storms always move in from west to east or from northwest to southeast?
Tom Vogt, Orland Park IL
Dear Tom,
You are correct to observe that most moving weather systems (low- and high-pressure systems) approach Chicago from a westerly direction. At the surface, the Earth’s atmosphere is divided into several permanent, although undulating, belts of wind which are oriented approximately parallel to the equator. This is called the primary circulation.
One of those circulation belts extends from about 35 to 55 degrees north latitude. Chicago lies within this belt, and the main motion of air is to the north. However, the Coriolis deflection, which acts to the right of the attempted northward motion, results in the north-blowing winds turning east. This belt is thus called the prevailing westerlies.Dear Tom,
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Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
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