How do meteorologists define a wind gust?

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Dear Tom,
How do meteorologists define a wind gust? What is the record high gust in Chicago?
Glenn Kaminski New Buffalo, MI.

Dear Glenn,
A wind gust is defined as a rapid fluctuation in wind speed, usually less than 20 seconds. According to Chicago climatologist Frank Wachowski, there must be a variation of at least 10 knots (12 mph) between the peaks and lulls of the wind speed. Gusts tend to be higher in unstable situations when cold air moves over warmer ground or over water. During outbreaks of cold air, wind gusts may exceed the average wind speed by as much as 30 mph. During thunderstorms, rain-cooled air from a cumulonimbus cloud may generate wind gusts in excess of 100 mph. Chicago’s highest gusts- 88 mph, recorded during an early-morning thunderstorm at Midway Airport on August 26, 1965, and 84 mph at O’Hare Airport, during a thunderstorm on March 27, 1991.


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