Recognition of Negative Mesoscale Factors for Severe-Weather Potential: A Case Study

Abstract

The case of 7–8 June 1998 in eastern New Mexico and western Texas is used to illustrate the challenge of recognizing possible negative effects created by mesoscale processes. In this case, a region of cloud-covered cool air (which was associated with early thunderstorms) may have limited the tornadic potential of severe convection. Although the tornado potential in the synoptic situation was not highly portentous, supercell storms did eventually form, one of which was persistent for many hours. There were only relatively brief and weak tornadoes reported from this storm early in its life, despite its persistence as a long-lived supercell that produced a long swath of large hail. In this case, the development of thunderstorms east of the threat area early in the day maintained cloudiness that apparently inhibited the destabilization of the surface-based air mass over which the afternoon thunderstorms eventually moved. The persistent supercell formed on the dryline but overrode this mesoscale cool air mass relatively soon after it developed. It was able to persist as an elevated supercell despite the relatively stable near-surface air mass, but its tornadic production may have been limited by its interaction with this mesoscale feature. Implications for operational forecasting and warnings are discussed.