Oklahoma Panhandle Downbursts: 14 July 2009

During the afternoon of 14 July 2009, a cold front tracked through the Oklahoma Panhandle, bringing relief from a week-long heat wave. The cold front also triggered strong convective storms and resulting downbursts. The pre-convective environment downstream of the cold front over the panhandle was unstable with a well-mixed convective boundary layer and a steep temperature lapse rate below the 600mb level. Elevated Geostationary Operational Environmental Satellite (GOES) imager brightness temperature difference (BTD) values and Microburst Windspeed Potential Index (MWPI) values in the vicinity of downburst occurrence over the Oklahoma Panhandle served as evidence of the presence of a convective mixed layer. Strong downbursts that were recorded by Boise City and Beaver, Oklahoma Mesonet stations at 2015 and 2315 UTC, respectively, resulted from sub-cloud evaporation of precipitation. These downbursts occurred in proximity to moderate to high microburst risk values as indicated in the 1800 and 1900 UTC GOES microburst products.


The images above are a Geostationary Operational Environmental Satellite (GOES) imager microburst product at 1800 UTC (top) and a corresponding GOES sounder Microburst Windspeed Potential Index (MWPI) product at 1900 UTC 14 July 2009 (bottom), with the location of Oklahoma mesonet observations (BOIS, BEAV) of downburst wind gusts plotted on the images. The GOES microburst products displayed convective clouds developing along a weak cold front over the western Oklahoma Panhandle that would soon trigger strong convective storms. It is apparent in the product images that elevated risk values are associated with the classic "inverted V" profile as displayed in the image below, a Rapid Update Cycle (RUC) model analysis sounding over Boise City, Oklahoma at 1800 UTC. Downburst wind gusts of 48 knots and 40 knots were observed at Boise City and Beaver at 2015 and 2315 UTC, respectively.

Elevated risk values indicated the presence of a dry subcloud mixed layer with a steep temperature lapse rate up to 600 mb that favored the development of intense downdrafts due to the evaporation of precipitation and resulting negative buoyancy. This favorable environment was most effectively shown in the above sounding profile over Boise City at 1800 UTC.