SPC Mesoscale Discussion: Severe Thunderstorm Watch 418… 419…

SUMMARY…Damaging wind gusts will continue across portions of southeast KY into western, middle and parts of eastern TN this evening. The threat should increase across parts of northern MS/AL later tonight as the bow echo develops south/southeast over the next several hours.

DISCUSSION…Strong to severe gusts continue with the bow echo shifting southeast from south-central KY into middle and western TN and adjacent portions of eastern AR. The most recent measured severe gust was from Fort Campbell KY where a peak gust of 55 kt was measure in the last hour or so. Additional strong gusts from 40-50 kt have been noted across western TN and northeast AR with an accompaniment of additional damaging wind mPING reports scattered around the region. Western portions of the line across eastern AR into western TN have tended to weaken as expected. 00z RAOB from LZK shows strong capping while the BNA RAOB is only weakly capped with impressive midlevel lapse rates and vertical shear profile. Indeed, portions of the line approaching middle TN have increased recently and may be taking advantage of this better quality thermodynamic/kinematic parameter space. Furthermore, VWP data from KHPX and KPAH have indicated a rear-inflow jet of 60-70 kt. Thus, it seems likely the portion of the bow from middle TN into southeast KY will continue to progress southeast along the instability gradient into parts of eastern TN and northern AL over the next several hours. While tornado threat appears low compared to damaging wind threat, 0-3 km shear of 32 kt with a sharply curved low level hodograph indicates at least some low-end threat for mesovortex tornadoes. Western portions of the line should gradually weaken as capping increases and deep layer shear weakens with southward extent per LZK and JAN 00z RAOB. Further east, instability decreases rather abruptly across eastern KY and far northeast TN. A marginal threat for gusty winds may persist outside of current severe thunderstorm watches, but a downstream watch is not expected further east at this time given a rapid decrease in supportive environmental conditions.

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