HELENA - A heat burst is a sudden, localized increase in air temperature near the earth's surface that typically occurs at night and are associated with decaying thunderstorms.
Several instances of heat bursts have occurred in Montana recently. On July 18 in echo, Montana, at 3 a.m. the temperature was 70º, but by 5 a.m. the temperature inexplicably climbed to 87º. On July 15 in Delta, Montana, the temperature was a cool 67º at 2 a.m. In less than two hours the temperature climbed nearly 20 degrees all the way up to 85º in the middle of the night. Wind also gusted up to 45 mph.
Timing is everything. Thunderstorms typically build through the afternoon and evening, when daytime heating is at a maximum. Storms thrive off of rising hot air, but at night when the sun goes down, storms lose that energy or fuel and begin to decay at night.
The storm literally collapses, with all of that upward vertical motion now falling toward the ground at a high rate of speed. The descending air increases pressure and begins to warm as it compresses hitting the ground.
Momentum carries the warm if not hot air across the surface of the earth with strong wind. Heat bursts can warm the temperature by more than 30 degrees at night, but only are temporary and temperatures can cool back down after the burst occurs.