U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 190453 
Storm Prediction Center ac 190452 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1052 PM CST Sat Nov 18 2017 

Valid 191200z - 201200z 

..no thunderstorm areas forecast... 

thunderstorms are not expected Sunday over the Continental United 


In the wake of a strong surface cold front, a generally cool, dry, 
and stable airmass will continue to filter southward across the 
eastern United States on Sunday. Although surface dewpoints will be 
in the 60s along and ahead of the front across the Florida 
Peninsula, weak convergence along the front and warm temperatures 
aloft should preclude thunderstorm development. 

Elsewhere, shallow convection associated with lake-effect 
precipitation may have the potential for a couple of lightning 
strikes, but confidence and coverage is too low to justify 
delineation. Additionally, as a low-amplitude mid-level trough moves 
across the Pacific northwest, sufficient cooling aloft may result in 
enough mid-level instability to produce a lightning strike or two 
along and near the immediate coast. 

.Marsh.. 11/19/2017 


Mesoscale Discussion

acus11 kwns 182324 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 182324 

Mesoscale discussion 1773 
National Weather Service 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 www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 34048819 36588602 36588440 36278421 34978545 34268621 
33988719 33918800 34048819