Mesoscale Discussion — Tornado Watch Possible for Portions of North Alabama

SUMMARY… A narrow evolving line of heavier showers and embedded thunderstorms may overspread the region through mid to late afternoon, with at least some potential for brief strong to locally damaging wind gusts.

DISCUSSION… A narrow line of enhanced convection, with embedded thunderstorms, has gradually evolved, perhaps aided by frontogenetic forcing, and appears likely to advance rapidly east-northeastward across the Mid South through 22-00Z. This is nearly coincident with an intensifying lower/mid tropospheric speed maximum, including speeds of 70-90+ kt in the 850-500 mb layer, overspreading the lower Ohio/Tennessee Valley vicinity.

Ahead of this activity, persistent preceding rainfall appears to have contributed to a deep tropospheric layer of moist adiabatic lapse rates, with model forecast soundings suggesting little change prior to the arrival of the convective line. Some model output indicate a more stable near-surface layer persisting as well, but the Rapid Refresh forecast soundings indicate lapse rates may trend at least closer to moist adiabatic just ahead of the line. Regardless, this seems likely to minimize the potential for vigorous downdrafts. Furthermore, forecast soundings also suggest that low-level hodographs will trend more linear with the arrival of the line.

Given these trends, the evolution of an appreciable severe weather threat is uncertain. However, due to the strength of the wind fields just above the surface, downward mixing of potentially damaging wind gusts might not be out of the question, particularly aided by the narrow heavier rain band.

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