05/04/2016
Great post about a heat burst that occurred in Sussex County on Monday evening!
You can read more about heat bursts from the Norman, OK NWS Weather Forecast Office: http://www.crh.noaa.gov/oun/?n=heatburst_info.
When you run a network of weather stations, which we often refer to as a mesonet, you see LOTS of data...all the time. While looking through the data is part of the job, we're particularly intrigued when we have thunderstorms move through our network like what we saw late Monday evening. Every once in awhile, we get lucky and see something unusual. As we reviewed data from Monday night, we noticed something very peculiar that we don't see very often around here in the air temperature data at Harbeson: a 7 degree F increase in air temperature in 15 minutes following a pretty nice downpour (see graphs of small temperature spikes around 2300 hours at both Harbeson and Stockley in eastern Sussex County, DE). Most of the time when it rains this time of year, we expect it to cool us down, not INCREASE the temperature. So why would the air temperature increase at Harbeson? It's due to a lesser known phenomenon (at least for those of us in the Eastern U.S.) called a heat burst. A heat burst can occur when a thunderstorm begins to decay (or die) and dry air is pulled in from aloft. As that dry air gets pulled in, it cools and becomes denser than the air around it. As the thunderstorm starts to run out of energy, this dense pocket of cool, dry air begins to descend, warming as it goes, before finally reaching the ground. In the most extreme cases, heat bursts can increase surface temperatures by 20-30 degrees in only a few minutes and are sometimes associated with strong winds. For our decaying thunderstorms Monday night in Sussex County, this wasn't the an extreme event and thankfully we didn't see the strong, gusty winds with this heat burst. But it was still a nice "treat" for us weather geeks who enjoy a rarity like this. Heat bursts are most common in the Great Plains in the United States and most often occur at night, particularly during late Spring/early Summer. So at least this event matched the seasonal climatology pretty well. Heat bursts aren't unprecedented on Delmarva though. A much stronger heat burst (temperature increase of 13 degrees F) occurred near Salisbury, MD on April 26, 2009. While the heat burst on May 2nd was much smaller, it was still interesting to see it happen in not one but 2 DEOS stations as the storm died out crossing Sussex County. Not many systems can detect a heat burst like that.
