Mesoscale Discussion

ACUS11 KWNS 182324
SPC MCD 182324 
Mesoscale Discussion 1773
NWS Storm Prediction Center Norman OK
0524 PM CST Sat Nov 18 2017
Areas affected...Portions of Tennessee and northern Alabama
Concerning...Severe Thunderstorm Watch 517...
Valid 182324Z - 190130Z
The severe weather threat for Severe Thunderstorm Watch 517
SUMMARY...A squall line will continue east within and near Watch 517
this evening, with an attendant threat of a few damaging gusts and
perhaps a tornado. The line should gradually weaken with eastward
extent this evening, such that downstream watch issuance is not
currently anticipated.
DISCUSSION...A nearly continuous line of thunderstorms is advancing
across Tennessee and northern Alabama early this evening. Over the
last hour, there was a localized uptick in tornado potential
south/east of the Nashville area, with three distinct tornadic
debris signatures in Rutherford, Wilson, and Trousdale counties.
While cells will continue to outpace remaining low-level buoyancy,
impressive low-level shear may still yield a quick tornado across
Middle Tennessee over the next hour. Otherwise, an isolated damaging
wind threat will likely persist through the 01Z expiration time of
Watch 517.
Farther south, convection has at times consolidated into a few
stronger segments over northern Alabama. Local observations have yet
to indicate severe wind gusts, but considering the strength of
low-level flow and presence of weak mixed-layer CAPE, isolated
damage will remain possible for the next couple hours, before
surface-based buoyancy is shunted farther south.
..Picca.. 11/18/2017
...Please see for graphic product...
LAT...LON   34048819 36588602 36588440 36278421 34978545 34268621
            33988719 33918800 34048819