Last night, Sioux Falls, SD, experienced a rather weird and rare weather phenomenon. It’s called a Convective Heat Burst.
My wife and I woke up at about 4 a.m. this morning to the sound of high winds and tree branches hitting the roof. I looked out the back window & saw that a large branch had fallen, so I went out to check to see if there was any damage. Stepping out the back door was like walking into a sauna — hot!
Thankfully, there wasn’t any damage to our house — the large branch had fallen between our house and the neighbor’s garage — but there were small branches everywhere. The wind died down shortly afterward, and I could feel the temperature dropping while I was out there. It was strange; really strange.
Today I went digging around on the Internet to see what I could find out; the local news station had a blurb on their website about it, and Wikipedia has a page on it (even updated with last night’s event; how about that!)
Meteorologists don’t know exactly what causes a heat burst; they theorize that rain hits a pocket of dry air at about 10-20,000 feet and quickly evaporates. The evaporating moisture causes the air to become more dense than the surrounding air, which causes it to descend rapidly, compressing that air mass, and the compression causes the temperature of the air mass to rise. When that mass of air hits the ground, you get high winds and hot, dry air.
How hot? Last night, the air temperature went from 72°F to 101°F in a matter of minutes, then back down just as quickly. According to the Wikipedia entry, a heat burst occurred in Brazil in 1949 causing the temp to jump from 100°F to 158°F in two minutes!
I had never even heard of a heat burst before, much less experienced one, so in a way I’m glad for the large branch laying in my yard; if it weren’t for that I wouldn’t have been outside at 4a.m. to experience the heat; if it weren’t for that I wouldn’t have been curious enough to go looking for the reason behind that and the wind accompanying it.