U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 260041 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0741 PM CDT Wed Apr 25 2018 


Valid 260100z - 261200z 


..there is a marginal risk of severe thunderstorms across parts of 
south Texas... 


... 
Isolated strong to severe thunderstorms may continue to affect parts 
of south Texas this evening. 


..south Texas... 
The latest water vapor imagery shows an upper-level low over the 
central states with an upper-level trough extending southwestward 
into the Southern Plains. The southern extension of the trough is 
located across the lower Rio Grande Valley and a plume of mid-level 
moisture is present ahead of the trough along the Texas coastal 
plain. Scattered thunderstorms are ongoing within this plume along a 
corridor of instability. The rap is analyzing this corridor of 
instability across the western part of south Texas where MLCAPE 
values are estimated in the 250 to 500 j/kg range. In addition, the 
00z soundings at Corpus Christi and Brownsville both have 45 to 50 
kt of 0-6 km shear with some directional shear in the lowest 3 km 
above ground level. This combined with steep mid-level lapse rates around 7.5 c/km 
may be enough to continue a marginal severe threat for a couple more 
hours. However, as storms approach the Lower Texas coast this 
evening where instability is considerably weaker, convection should 
gradually weaken. 


.Broyles.. 04/26/2018 


$$ 

Mesoscale Discussion


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Mesoscale discussion 0289 
National Weather Service Storm Prediction Center Norman OK 
0324 PM CDT Wed Apr 25 2018 


Areas affected...parts of south Texas 


Concerning...severe potential...watch unlikely 


Valid 252024z - 252230z 


Probability of watch issuance...20 percent 


Summary...a severe storm or two -- with potential to produce hail 
and/or locally damaging winds. Ww is not anticipated at this time 
due to anticipated limited coverage of risk. 


Discussion...latest radar loop shows a cluster of thunderstorms near 
and west of the Sat area, along a cold front moving steadily 
southward across south Texas. Other, stronger cells are ongoing 
well west of the Rio Grande over northeast Mexico -- where much 
greater instability is observed. 


With that said, the eastern extension of the axis of stronger 
instability extends just across the river into Laredo/Cotulla area, 
south of the ongoing storms. As the front advances southward into 
this area, a couple of more vigorous storms may develop. While 
shear remains somewhat modest across the area -- only marginally 
supportive of mid-level rotation, some risk for hail and or damaging 
winds may evolve locally late this afternoon and early evening. 


.Goss/Hart.. 04/25/2018 


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


Attention...WFO...crp...ewx... 


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