U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 191631 
Storm Prediction Center ac 191629 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1029 am CST Mon Feb 19 2018 

Valid 191630z - 201200z 

..there is a marginal risk of severe thunderstorms late this 
afternoon through tonight across parts of the Southern Plains... 

A few strong to severe thunderstorms are possible over a portion of 
the Southern Plains, mainly late this afternoon into tonight. 

..Southern Plains to the MS valley through tonight... 
An amplified large-scale pattern with a western trough and eastern 
ridge is now established and should persist for the next several 
days. An expansive warm sector is in place from the mid MS valley 
and Southern Plains to the Gulf Coast, with boundary-layer dewpoints 
ranging from near 60 f north to the upper 60s along the coast. This 
moist warm sector is supportive of clusters of slightly elevated 
convection in multiple clusters, primarily focused along the 
low-level jet corridor where warm advection is maximized from OK to 
MO. Conditionally unstable midlevel lapse rates (around 7 c/km) and 
the low-level warm/moist advection will continue to support elevated 
thunderstorms through the period, though clouds will tend to limit 
surface heating from eastern/northern OK northeastward along a 
slow-moving front. 

Some cloud breaks are more probable this afternoon from western OK 
into northwest TX, where surface heating will boost MLCAPE values 
into the 1000-1500 j/kg range with only weak convective inhibition. 
However, forcing for ascent will also be weak at best along the 
dryline south of the triple point near I-40 along the OK/Texas border, 
and storm initiation is somewhat in question. If isolated storms do 
form this afternoon/evening, buoyancy and vertical shear will be 
sufficient for supercells capable of producing large hail and 
perhaps an isolated tornado. The odds for storm development should 
increase later this evening through tonight from southwest/central 
Texas into central OK, as an embedded shortwave trough (now over baja) 
ejects northeastward and interacts with the unstable warm sector. 
Embedded supercells and/or short bowing segments will be possible, 
with an associated threat for isolated large hail/damaging winds, as 
well as an isolated tornado. Will maintain the low severe 
probabilities in this update, but there will still be some potential 
for an upgrade in later outlook updates across parts of TX/OK. 

.Thompson/Cook.. 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