Why is the temperature spiking? At night?
Severe thunderstorms, tornadoes, hail, flooding, and lightning are something we're used to here in the Ozarks. What we're not used to is temperatures skyrocketing to 101˚F at night. Wild right?
This rare event happened in Springfield the night of Friday, June 11th.
Let's look at the observations, courtesy of the National Weather Service in Springfield. The sun had set, and temperatures had already cooled to the upper 70s after the passage of strong storms (notice the second from the right temperature column outlined in yellow).
Unexpectedly, temperatures jumped from 78˚F to 101˚F, in just five minutes (outlined in red). The triple-digit temperatures only lasted two minutes, but it was still in the 90s for a while after. A drop in the dew point, pressure, and strong winds accompanied the temperature jump.
This rare weather phenomenon is known as a heat burst. As the name suggests, a heat burst is just a burst of dry and hot air rushing out from a thunderstorm. They are rare because the atmosphere needs just the right conditions for them to occur. Full disclosure, this was the first heat burst I had ever personally experienced.
Heat bursts typically occur in the evening or at night in the wake of dying thunderstorms. If you look at radar imagery from the night of the 11th, a decaying cluster of thunderstorms had just passed around Springfield.
Heat bursts originate from very high up in the thunderstorm in a region of dry air. As thunderstorms begin to dissipate, downward moving air, known as a downdraft, dominates the storm causing it to weaken.
Downdrafts develop when warm and dry air is present in the mid-levels of the atmosphere. Any rain within this region will quickly evaporate. Now, evaporation actually cools the downdraft, but since it is still relatively warmer than the air around the storm, it descends. Just as the air cools as it rises in the lower levels of the atmosphere, air also warms back up as it falls to the surface. The warming of air as it falls counteracts the cooling occurring because of the evaporation of precipitation.
When the descending air hits the surface, it spreads out in all directions producing damaging winds. The heat burst on June 11th left behind a boundary that caused strong winds for the next several hours. Those wind gusts were upwards of 50mph and led to a few downed trees and powerlines. If you scroll back up to the radar imagery, notice how these were non-thunderstorm winds. There was no rain or storms associated with them.
As mentioned previously, the temperature in Springfield jumped about 23˚F because of the heat burst. Get this, some heat bursts can be so intense that they cause a 50˚F temperature jump! It can take several hours for temperatures to return to normal after such a spike.
I also mentioned previously that the air in a heat burst is very dry. Just how dry? Before the heat burst on the 11th, dew points were in the 60s, which is muggy. Around the time we had the triple-digit temperatures, the dew point dropped to the low 40s, which is dry!
These events are rare. So the fact we even had one Friday night was incredible. Now you can add heat bursts to the list of crazy weather events we see here in southwest Missouri.
Heat bursts are also not the same thing as microbursts, which is another phenomenon of air descending through dying storms and causing strong winds. Next week, I'll explain the difference.