Heat Burst hits SW IA Tuesday evening
August 24th, 2011 by Ric Hanson
If you noticed it became unusually, and suddenly hot Tuesday evening here in Atlantic, and in the surrounding area, you weren’t imagining things. The National Weather Service in Des Moines says a rare phenomenon known as a “Heat Burst” affected portions of southwest Iowa. A Heat Burst is characterized by a sudden rise in temperature, a drop in humidity, and strong winds that can approach or exceed severe levels. They are associated with high-based decaying thunderstorms with a substantial dry layer between the base of the storm.
As rain from the thunderstorm falls into the underlying dry air, it cools the air immediately around it, which becomes denser than the surrounding air, and begins to sink. As this air sinks, it dries and compresses, resulting in the hot and dry readings recorded with heat bursts.
Here in Atlantic, at the KJAN studios…the official National Weather Service reporting station…our temperatures from 1-to 6-pm were generally in the mid-80’s. The high here at the station reached 97-degrees.
According to the Automated Weather Observation System located at the airport, just before 7-p.m., the winds began to increase from 15- to 30-miles per hour. By 7:15, were gusting upwards of 40-miles per hour, and the temperature jumped from 88-degrees at 6:55-p.m., to 99-degrees at 7:15. The temp maxed out at 102-degrees, 10-minutes later, and by 7:35 had dropped to 91. The air cooled to the mid 80’s by 8-p.m.
The phenomenon also brought some damaging winds to part of the listening area. Officials with the Weather Service say a Heat Burst-related wind event caused a tree to fall on a power line in Bridgewater, at around 6:50-p.m. At 7:05, a tree was observed down on a power line one-mile south of Brayton. Other tree limbs also fell, as winds of up to 40-miles per hour occurred. The temperature in that area also spiked, from 76- to 96-degrees in just a few minutes. There was also a sharp drop in the humidity. And, a 60-mile per hour gust of wind was recorded in Fontanelle at 7:44-p.m., by an automated system.