U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210551 
Storm Prediction Center ac 210549 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1149 PM CST Mon Nov 20 2017 

Valid 211200z - 221200z 

..no severe thunderstorm areas forecast... 

little, if any, severe weather is expected across the contiguous 
United States Tuesday or Tuesday night. 


A series of mid-level troughs will move across the United States on 
Tuesday, downstream of an amplifying ridge across the west, 
resulting in mean troughing across the east. One of these troughs, 
albeit weak, will lift northeast from the Gulf of Mexico, across the 
Florida Peninsula, into the Gulf steam waters off the Carolina 
coast. Modest ascent associated with this wave, combined with a 
remnant front lifting north across the peninsula, will yield the 
potential for a few showers and thunderstorms during the day. 
Overnight, this area of showers and thunderstorms will develop 
northeast toward the coastal areas of north and South Carolina. 

Forecast soundings across Florida suggest decent mid-upper-level 
shear, which may lead to an isolated severe report. However, weak 
lower-level winds and the lack of more robust low-level convergence 
should preclude appreciable coverage of severe weather. 

Elsewhere, another mid-level troughs will dig southward across West 
Texas into northern Mexico. Modest ascent associated with this 
trough will help induce surface troughing off the southeast Texas 
coast. In turn, surface winds will become more easterly across far 
East Texas and the northeast portion of the Texas coastal waters. 
The resulting increase in low-level convergence, combined with the 
weak ascent from the mid-level trough, may result in showers and 
thunderstorms across southeast Texas. 

.Marsh.. 11/21/2017 


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