U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 190052 
Storm Prediction Center ac 190051 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0651 PM CST sun Feb 18 2018 

Valid 190100z - 191200z 

..no severe thunderstorm areas forecast... 

a few thunderstorms are expected over the Southern Plains this 
evening, expanding into the middle Mississippi Valley tonight. 
Sporadic lightning strikes remain possible along the California and 
southern Oregon coasts 

..Southern Plains through the middle Mississippi Valley region... 

Weak impulses embedded within the southwesterly southern-stream flow 
will move northeastward through the Southern Plains and middle MS 
valley region tonight. This in conjunction with modest isentropic 
ascent, Theta-E advection and destabilization resulting from a 
strengthening southerly low-level jet will promote development of 
showers and thunderstorms tonight, initially over the Southern 
Plains, then gradually expanding northeastward through the middle MS 
valley. Thunderstorm coverage should remain isolated over the 
Southern Plains where more substantial warming in the 850-700 mb 
layer will contribute to at least a modest capping inversion. A 
couple instances of small hail remain possible in this area where 
steeper mid-level lapse rates and greater instability reside. 
Eventually, more numerous showers and thunderstorms may form toward 
the middle MS valley region late tonight or early Monday within zone 
of strengthening low-level Theta-E advection. 

.Dial.. 02/19/2018 


Mesoscale Discussion

acus11 kwns 182148 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 182147 

Mesoscale discussion 0071 
National Weather Service Storm Prediction Center Norman OK 
0347 PM CST sun Feb 18 2018 

Areas affected...parts of West Texas 

Concerning...severe potential...watch unlikely 

Valid 182147z - 182245z 

Probability of watch issuance...5 percent 

Summary...at least isolated strong to severe storm development 
appears possible during the 4-6 PM CST time frame, with severe hail 
and locally strong wind gusts the primary potential hazards. 

Discussion...weak to moderate destabilization is ongoing near the 
dry line across West Texas, with continued boundary layer heating 
and mixing. Latest rap output suggests cape is now on the order of 
500-1000 j/kg. Low-level convergence appears weak, and mid/upper 
forcing for ascent unclear, but inhibition appears to be in the 
process of becoming increasingly negligible. At least isolated 
thunderstorm development does not appear out of the question within 
the next hour or two, probably near or west/southwest of Midland, 
based on latest visible imagery. 

Given favorable deep layer shear beneath southwesterly mid-level 
flow on the order of 40-50 kt, any sustained convection could take 
on a supercell structures. This probably would be accompanied by at 
least the risk for severe hail and localized strong surface gusts, 
before boundary layer instability wanes after nightfall. 

.Kerr/Thompson.. 02/18/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 31250339 32360272 33110158 33120058 32100184 31550236 
30670330 30880347 31250339