Heat bursts are sudden, usually dramatic increases in the surface temperature, often accompanied by strong winds, that sometimes occur in the vicinity of a thunderstorm. Though they are not an everyday occurrence, they are not exceptionally unusual either.
A recent example from Wichita, Kan., summarizes the characteristics of these interesting phenomena. At 12:22 a.m. on Thursday, the temperature at Wichita’s Mid-Continent Airport was 85 degrees with a dewpoint of 60 degrees. At 12:42 a.m., just 20 minutes later, the temperature was 102 degrees, the dewpoint dropped to 30 degrees and the winds were gusting in the 40 to 50 mph range.
A similar phenomena occurred just west of Milwaukee on Wednesday morning when Milton, Whitewater, Fort Atkinson, and the National Weather Service Forecast Office at Sullivan reported temperature increases of between 7 and 16 degrees, dewpoint decreases of between 8 and 19 degrees, and gusty winds in the 35-55 mph range.
Milton’s temperature went from 76 degrees to 92 degrees while its dewpoint dropped from 65 degrees to 46 degrees while winds gusted to 42 mph.
A line of rain showers with cloud bases at about 12,000 feet moved through the area on Wednesday morning. The air beneath the cloud base had a very low relative humidity and supported rapid evaporation of the falling raindrops. The evaporation led to cooling of the air at cloudbase which rendered it heavier than its surroundings and it accelerated toward the surface.
As the air sinks to lower elevation (higher pressure) it is compressed and warms up — in cases such as this one, the warm-up is extreme and led to the heat burst.