U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 191218 
Storm Prediction Center ac 191217 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0617 am CST sun Nov 19 2017 

Valid 191300z - 201200z 

..no thunderstorm areas forecast... 

thunderstorms are not expected through tonight across the Continental U.S.. 

A midlevel shortwave trough and associated surface cyclone will move 
across New England by early afternoon, while a trailing cold front 
continues southeastward across Florida. Marginal low-level moisture, 
warm temperature profiles aloft, and only shallow/weak forcing for 
ascent along the front in Florida suggest that thunderstorms are 
unlikely. Otherwise, a positive-tilt midlevel trough will approach 
the Pacific northwest coast overnight. Forecast soundings from the 
NAM/GFS/rap show weak midlevel buoyancy after 03-06z (100-200 j/kg 
MUCAPE rooted in the 800-700 mb layer) within the pre-frontal warm 
advection regime. While an isolated lightning strike cannot be 
ruled out, the overall thunderstorm threat appears too marginal to 
warrant an outlook area. 

.Thompson.. 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