Heat Burst Affects Northwestern Oklahoma

 

Heat Burst Affects Northwestern Oklahoma

A heat burst occurred over parts of northwest Oklahoma last night, beginning around 10 pm and lasting until around 5 am. Temperatures well after dark warmed above 90 degrees, and winds gusted 55 to 65 mph at times as seen in the map below. The event lasted between one and two hours at a specific site, which is right about average. Luckily, no damage was reported with the strong winds.

Max Temperatures and Winds That Occurred during the Heat Burst Event in Northwestern Oklahoma on June 11, 2010

We are getting into that time of year when heat bursts become more common, and many questions arise about the origins of these phenomenon. More research has been done on heat bursts recently, so we are getting a better understanding on why they occur, and can even forecast these in advance. Some facts about heat bursts are:

  • They usually occur during the evening or overnight hours due to decaying thunderstorms.
  • Not all decaying thunderstorms produce heat bursts.
  • They are characterized by a rapid increase in temperature, with an equally sharp decline in the dew point temperature. The temperature can rise 10 to 20 degrees in a matter of minutes.
  • Wind speeds are accelerated from high in the cloud tops and, in some cases, can exceed 90 mph once they reach the surface. However, wind speeds usually average 40 to 45 mph. Significant damage can occur, depending on the strength of the wind speed, and the duration of the event.
  • More common in the late spring and summer months.
  • Typically last around an hour, but can last for several hours.
  • Most common across the plains states, but can happen everywhere.

Last night a thunderstorm complex moved out of the Texas panhandle and moved into stable air over Oklahoma. The 00Z upper air sounding out of Dodge City, KS (close to where the heat burst occurred) showed a large column of dry air below 500 mb. The sounding from Norman, OK also showed the column of dry air, although not quite as significant. As the thunderstorms moved east into this less favorable environment, they began to decay. Basically, the updraft in the thunderstorm shut off, leaving only the downdraft portion of the storm. As the precipitation in the downdraft fell into the environmental dry air, it evaporated and cooled. The cooler air was now very dense and further accelerated toward the ground. After all the precipitation has evaporated, the air no longer cools, but begins to warm up due to compression. The air now is warming dramatically and has now  become more buoyant (warmer than its surroundings), and it slows down. Even though it is slowing down, the downward momentum is so great that the downdraft makes it all the way to the surface. Winds in excess of 50 mph were reported, and temperatures warmed into the upper 80s and lower 90s. The peak wind gust occurred at Gage ASOS, measuring 66 mph and the highest temperature occurred in Harper county, reporting 93 degrees.

Graphic Depicitng the Heat Burst Process

Significant heat burst events have occurred in the past, with the most signficant even occurring on May 22nd, 1996. The temperature at Chickasha and Ninnekah both rose above 100 degrees, and winds in excess of 60 mph were reported over several areas in southwest Oklahoma. Damage to trees, power lines, and rooftops was reported. Other stories (unverified) claim to have seen the temperature rise well over 100 degrees. These extreme events are rare, but are quite signficant when they occur.

 



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