West Texas Mesonet observations of wake lows and heat bursts across northwest Texas

The heat burst is characterized near ground level by a rapid increase in temperature, decrease in dewpoint, falling pressure, and the onset of high winds. Previous studies have established two moist convective processes that may initiate heat bursts. The first is akin to the thunderstorm downburst or microburst. In this case, the heat burst is formed when the evaporation or sublimation of hydrometeors in a thunderstorm downdraft creates a negatively buoyant air parcel, whose downward momentum is sufficient to penetrate a stable surface layer (the majority of heat burst events occur at night, when a nocturnal inversion is present). In the case of the heat burst, the evaporative cooling is not adequate to maintain saturation of the air parcel, and while the descending parcel thus becomes warmer than the surrounding environment; its momentum brings it down to the surface. The second case is the result of the development of a wake low in the trailing stratiform precipitation region of a mesoscale convective system. Wake lows are thought to be generated by subsidence warming brought about by a rapidly descending rear-inflow jet. In this case, a heat burst may be associated with an enhancement of this descending jet by downdrafts of individual decaying convective cells.

The thermodynamic environment that supports wake lows and heat burst development is most commonly observed in the high plains during the warm season. While documented heat bursts are infrequent due at least in part to the sparsely populated nature of this region, the recent expansion of surface mesonetworks are increasing the likelihood that these events will be sampled. The West Texas Mesonet, a collection of over forty meteorological stations spread across the Panhandle and South Plains of northwest Texas, has captured over 10 heat burst events during the period 1 June 2004 to 30 June 2006. These stations measure meteorological variables at five-minute intervals (including peak two-second wind gusts). During these events, many of the stations recorded surface wind gusts in excess of 26 m s^-1, and are thus considered severe winds capable of producing property damage and injury.

This paper will survey the mesoscale environment of the wake lows/heat bursts through analyses of the West Texas Mesonet stations augmented by supporting radar, satellite and profiler data. It is hoped this information will prove useful to forecasters to predict the onset and evolution of heat bursts.