Heat bursts are sudden, usually dramatic increases in the surface temperature that are 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, KS summarizes the characteristics of these interesting phenomena. At 1222 AM, June 9, 2011 the temperature at Wichita’s Mid-Continent Airport was 85°F with a dewpoint of 60°F. at 1242 AM, just 20 minutes later, the temperature was 102°F, the dewpoint dropped to 30°F and the winds were gusting in the 40 to 50 mph range. You can see this on the image, look at the weather station labeled KICT. (If you don't remember how to decode the station model, you can do so here.
A similar phenomena occurred just west of Milwaukee on the morning of June 8, 2011 when Milton, Whitewater, Fort Atkinson, and the National Weather Service Forecast Office at Sullivan reported temperature increases of between 7-16°F, dewpoint decreases of between 8-19°F and gusty winds in the 35-55 mph range. Specifically, Milton’s temperature went from 76°F to 92°F while its dewpoint dropped from 65°F to 46°F while winds gusted to 42mph. 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 lead to the heat burst.