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Posted at 01:00 PM ET, 06/10/2011

Extreme temperature swings: midnight heat burst in Wichita; mercury tanks in Chicago, Minneapolis

Since June began, no doubt the 1400-plus new heat records set across the U.S. have impressed. But consider the following: between midnight and 1 a.m. Thursday morning, the temperature in Wichita, Kansas spiked from 81 and 101 degrees. Yes- the temperature ROSE 20 degrees in one hour in the middle of the night, passing the century mark. To the north, across the Great Lakes and Upper Midwest, there were some remarkable - though not nearly as dramatic - temperature declines.

What happened in Wichita is known as a heat burst, a relatively rare phenomenon. At the website TheWeatherPrediction.com, meteorologist Jeff Haby describes what a heat burst is and how it develops. Here’s a short excerpt that captures the essence of it:

A heat burst is a downdraft of hot and dry air that typically occurs in the evening or overnight hours. . . . Heat bursts usually happen in the evening or at night after thunderstorms are ending. Thus, a thunderstorm has a vital role. Two other characteristics are that the air must start its descent from fairly high up and the environmental air aloft needs to be very dry.

Meteorologist Dan Satterfield explains how these conditions came together in Wichita in his blog WildWildScience:

... At around midnight a thunderstorm developed just south of Wichita, and set the stage for the heat burst.

As rain fell into the dry air layer at around 2-3 thousand meters above the surface, it evaporated rapidly. The evaporating rain cooled the air very quickly, and this cool air was now much heavier than the air around it. This heavy, rain cooled air, fell rapidly to the surface, but heated due to compression at the standard adiabatic rate of 10 C per 1000 meters. If it fell 2500 meters, then the temperature of that rain cooled air would have risen 25C!

That’s pretty radical.

UPDATE (3:15 p.m.): A little more detail on the heat burst: the Daily Mail reports that the temperature rose 17 degrees in 20 minutes in Wichita (from 85 at 12:22 a.m. to 102 at 12:42 a.m.) as winds gusted to 50-60 mph.

Haby’s website indicates the most extreme heat bursts last for a significant amount of time and have temperatures reach 120+ degrees

Several hundreds miles to the north, temperatures were changing in the opposite direction - albeit at a much less steep pace - in the wake of a cold front cutting through the Great Lakes.

Chicagoans experienced their largest 2-day June temperature drop in 23 years. Writes meteorologist Tom Skilling at the Chicago Weather Center:

Thursday’s temperature plunge was so extreme it was as if the city had been exposed to a switch in seasons in just 28 hours. That’s the time it took readings here to dive from a near record 95-degrees Wednesday to Thursday afternoon’s chilly low 50s. The 45 degree plunge at O’Hare fell just short of June’s all time record 2-day pullback of 49-degrees recorded between June 25 and 26, 1988. That period saw the temperature dive from 103-degrees to 54.

While Thursday’s thermal retreat was not a record, the cool-down was of a magnitude which has been observed in only four other Junes here over the past 141 years.

In Minneapolis, meteorologist Paul Douglas wrote on his Star Tribune blog: “Welcome to a Whiplash June, 103 on a Tuesday, light jackets on a Friday.” After a high of 103 in Minneapolis on Tuesday, Thursday’s high was just 68. Today’s forecast high: 59.

By  |  01:00 PM ET, 06/10/2011

Categories:  Extreme Heat, U.S. Weather, Latest

 
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