SPC Mesoscale Discussion: Severe Potential… Watch Unlikely

SUMMARY…Thunderstorms are expected to continue weakening trend from south-central KY into middle TN this evening. A marginal severe threat may persist further south into central/northeast MS and northwest AL for a couple more hours, but a watch is not expected.

DISCUSSION…After a brief uptick in convection across south-central KY into middle TN over the last hour or two, convection has trended toward weakening and a more disorganized state recently. Based on the 00z RAOB from BNA, steep midlevel lapse rates are still present, however, instability is meager with less than 200 J/kg MUCAPE indicated. Effective shear around 54 kt and a fairly large, curved low level hodograph gives some clues into the brief organization in convection earlier. But, with loss of daytime heating and increasingly poorer quality airmass with eastward extent, severe threat is expected to quickly diminish across KY/TN. Further south, convection has shown some upward trends in intensity as cells track east/northeast into central and northeast MS. Boundary layer moisture in better further south, with dewpoints in the low to mid 60s F resulting in MUCAPE around 500-750 J/kg per JAN 00z RAOB. A weak capping inversion near 700mb was still evident in this observation and is likely precluding more robust intensification. Convection therefore will likely continue to struggle in weaker forcing with southward extent. A marginal threat of a strong wind gust or hail may persist for a couple of hours across central/northeast MS into northwest AL as the cold front continues to push eastward this evening.

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