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Name: Jennifer Mundt L.
Status: educator
Age:  30s
Location: N/A
Country: N/A
Date: Tuesday, April 23, 2002

Why does Chicago have more rain in the spring than in the summer?

Dear Jennifer-

Most of the rain in the Chicago area in the spring and summer comes from moisture that is carried north from the Gulf of Mexico, and falls in the form of showers and thunderstorms.

The storm systems that produce the rain from the moisture brought north are more frequent in the spring than in the summer. Also, slightly less moisture is brought north during the summer, and the showers and thunderstorms are more isolated.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO

Jennifer, During Spring there is a greater gradient of temperature from north to south than there is in summer. There are still cold, dry air masses coming down from Canada and warm, humid air coming north from the southern part of the United States. At the boundary of these very different temperature and humidity regimes you get a lot of convection, (rising air), which transforms into strong cold fronts (with embedded thunderstorms), squall lines (made up of thunderstorms), and even isolated thunderstorms. These provide a lot of rain. In the summer, temperatures don't change from north to south as much and strong weather systems can't develop as easily or frequently, giving us less rain in the summer.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory

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