U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 220530 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1130 PM CST Thu Nov 21 2019 


Valid 221200z - 231200z 


..there is a marginal risk of severe thunderstorms across parts of 
southeast Texas and Louisiana... 


... 
Thunderstorms are expected from the Southern Plains into the lower 
Mississippi Valley today. A marginal tornado threat and potential 
for strong wind gusts will be possible. 


..southeast Texas/Louisiana... 
An upper-level low will move eastward across the Central High plains 
today as west-southwesterly mid-level flow remains over the Southern 
Plains. A cold front will advance southeastward onto the Texas 
coastal plains today. Thunderstorms may be ongoing along or ahead of 
the front at the start of the period. As the front moves 
southeastward across southeast Texas around midday, convective 
coverage should increase as surface temperatures warm and weak 
destabilization occurs. Forecast soundings this afternoon ahead of 
the front from Houston northeastward into north-central Louisiana 
increase MLCAPE to around 500-800 j/kg and have moderate deep-layer 
shear profiles. This environment should support a marginal 
wind-damage threat with the stronger cells ahead of the front. If 
isolated discrete cells can develop well ahead of the front along 
the instability corridor, then a marginal tornado threat will also 
be possible. 


.Broyles/nauslar.. 11/22/2019 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 212226 
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Mesoscale discussion 2151 
National Weather Service Storm Prediction Center Norman OK 
0426 PM CST Thu Nov 21 2019 


Areas affected...portions of south-central Arizona 


Concerning...severe potential...watch unlikely 


Valid 212226z - 220000z 


Probability of watch issuance...5 percent 


Summary...a couple of storms capable of producing marginally severe 
hail and gusty winds will affect areas in and around the Phoenix 
Metro area over the next couple of hours. Ww issuance will not be 
needed. 


Discussion...daytime heating (temperatures into the low 60s) beneath 
cold air/steep lapse rates aloft associated with the persistent 
upper low centered over the northwestern Arizona vicinity has 
permitted weak (less than 500 j/kg) surface-based cape to evolve 
south of the rim, particularly in the Phoenix Metro area and 
vicinity. This destabilization has been sufficient to support a few 
stronger updrafts, with vigorous storms now observed across portions 
of the northern half of Maricopa County. 


With an easterly component to the surface winds across the area, 
beneath 30 to 40 kt mid-level west-southwesterlies per the latest 
iwa WSR-88D vwp, resulting 0-6km bulk shear is supportive of 
organized/sustained updrafts. One cell in particular -- moving just 
east of kgyr (goodyear Municipal airport) -- has exhibited weak 
updraft rotation per radar data, and has produced hail approaching 
severe levels. 


Any risk for severe weather -- mainly in the form of hail -- should 
remain limited both spatially and temporally, given only a 
relatively small area of sufficient cape, and that expected to exist 
only through peak heating. With the onset of diurnal cooling in the 
next few hours, expect convective intensity to diminish. 


.Goss/grams.. 11/21/2019 


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


Attention...WFO...twc...fgz...psr... 


Latitude...Lon 33941355 34091220 33541130 33411022 33021027 32581146 
32851221 33081322 33481347 33941355