July 31, 2014

Rare “heat burst” hits Atlantic area

It wasn’t the earth-shattering news of an earthquake, but parts of southwest Iowa experienced a very rare weather phenomenon Tuesday evening. A so-called “heat burst” baked an area around Atlantic with a sudden rise in temperatures, a drop in humidity and strong winds.

Meteorologist Kevin Deitsch , at the National Weather Service, says a heat burst hits occasionally as thunderstorm clouds start to break up.

“What happens is, they’re raining really high aloft and that rain evaporates so you get cool air that forms under the storm,” Deitsch says. “This cool air, since it’s more dense than the air around it, starts rushing to the ground and when it does, it heats as it’s falling to the ground by compressional warming.”

Some areas of southwest Iowa saw temperatures jump from the 80s to as high as 102-degrees and then fall back into the 80s all within a matter of minutes. Deitsch says it’s all due to that phenomenon of falling air underneath the storm clouds.

“It’s coming all the way down from these bases at 18,000 feet,” he says. “Initially, it’s very cold, a lot colder than the environment, when it gets to the ground it warms up. By the time it actually hits the ground, it’s 10 or 15 degrees warmer than the air around it. That’s why we see these temperature spikes.”

The first heat burst struck shortly after 6 o’clock, winds gusted to 41-miles an hour and bounced the temperature from 84 to 93 degrees over the course of a few minutes. Deitsch says, “Then again, at 7:25, it went from the mid 80s all the way up to 102 and the dew point dropped all the way down to 7-degrees, which is pretty remarkable.”

That dew point rebounded to 75-degrees within minutes, along with the cooler temperatures. A report from Adair County says temps bounded from 76 to 96 within minutes, accompanied by wind gusts up to 60 miles an hour. Wind damage was reported to trees and power lines in Adair and Audubon counties — near Bridgewater, Brayton and Fontanelle. The heat burst and associated clouds would not have been anything remarkable to watch, but Deitsch notes, if you were outside, you certainly would have felt it.

See the full report from the National Weather Service at:www.crh.noaa.gov/news/display_cmsstory.php?wfo=dmx&storyid=72161&source=0