West Texas Windstorm: 14 August 2008

A convective high wind event over western Texas during the evening of 14 August 2008 served as another good example of the use of the Geostationary Operational Environmental Satellite (GOES)-West imager microburst algorithm. During the evening of 14 August, a cluster of convective storms that developed over eastern New Mexico merged with a larger mesoscale convective system (MCS) over the Texas Panhandle region, producing widespread high winds. A severe downburst, observed by Ralls (West Texas) Mesonet station, occurred in close proximity to elevated imager microburst risk values. The ambient thermodynamic environment over western Texas was typical of the southern Great Plains with a deep, well-mixed boundary layer that favored the development of intense convective downdrafts and resultant downburst generation.

The images above are the Geostationary Operational Environmental Satellite (GOES)-11 imager microburst risk product visualized with McIDAS-X (top) and McIDAS-V (bottom) software, valid at 2300 UTC 14 August 2008. The bottom image also displays radar reflectivity from Lubbock, Texas NEXRAD (KLBB) at 0235 UTC 15 August 2008, time of downburst occurrence. The imager microburst risk product (top) displays a large MCS over northwestern Oklahoma and the Texas Panhandle and a smaller convective storm cluster over eastern New Mexico. These two systems merged and produced widespread severe convective winds over western Texas. Also shown is the location of a severe downburst with an associated wind gust of 52 knots that occurred at Ralls (West Texas) Mesonet station, in close proximity to high microburst risk (orange shading). The bottom image, with overlying radar data, shows a bow echo over western Crosby county associated with the Ralls downburst. Note that the bow echo is located in a region of high microburst risk (orange shading), demonstrating the predictive value of this product for severe weather warning purposes.

The Rapid Update Cycle (RUC) sounding profile above, at Ralls, Texas at 2300 UTC 14 August, displayed a favorable thermodynamic environment with a steep temperature lapse rate and a well-mixed boundary layer. Comparison of the imager microburst product to the RUC sounding revealed that high risk values are associated with an "inverted V" profile. The West Texas Mesonet recorded 11 severe wind observations with this convective storm event, in which the majority of the high wind observations were associated with gust front passages. The downburst recorded at Ralls was distinctive in the meteogram above as a sharp peak in wind speed coincident with a peak in rainfall rate. Radar imagery at the time of downburst occurrence confirmed that the parent storm was overhead at the observing station. Thus, the Ralls downburst event was driven primarily by sub-cloud evaporation of precipitation and subsequent generation of negative buoyancy and downdraft acceleration- an "evaporatively initiated" downburst (Caracena and Flueck 1988).

REFERENCES

Caracena, F., and J.A. Flueck, 1988: Classifying and forecasting microburst activity in the Denver area. J. Aircraft, 25, 525-530.