WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.

Orographic lift

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Dear Tom,
I was reading my mom's old Nancy Drew book that mentions a cloud formation caused by "orographic uplift." What is that?
Chloe Brougham, 5th grader
Dear Chloe,
Orographic lift is a rising air flow caused by mountains. As air moving with the prevailing wind flow encounters a mountain range, it is forced to rise. This causes it to cool and condense, forming clouds and eventually rain if the air contains sufficient moisture. This process, known as orographic lift, is a major precipitation-producing mechanism. In the foothills of the Rockies, east winds push air up the eastern slopes, producing thunderstorms in summer and foggy, drizzly, rainy and snowy weather in winter. Orographic lift accounts for much of the precipitation in some of this planet's rainiest locations including Mt. Waialeale in Kauai, Hawaii; Mawsynram, India; and Lloro, Columbia.

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