U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 220548 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1148 PM CST Thu Feb 21 2019 


Valid 221200z - 231200z 


..there is a marginal risk of severe thunderstorms from East Texas 
into the lower Mississippi Valley... 


... 
Strong thunderstorms may impact portions of the lower Mississippi 
Valley this afternoon, expanding into the arklatex vicinity by late 
tonight, accompanied by at least some risk for severe weather. 


... 
A strong shortwave trough over the southwest is expected to 
intensify and become negatively tilted as it moves 
east-northeastward towards the Southern Plains by Saturday morning. 
In response, cyclogenesis is expected in the Lee of the southern 
rockies, and a cold front will begin to surge eastward into portions 
of West Texas late tonight. Further east, a warm front will move slowly 
northward during the day across portions of East Texas into the lower 
Mississippi Valley, with some acceleration northward into the 
arklatex region late tonight as the surface low deepens to the west. 


..lower MS valley region... 
Showers and scattered thunderstorms will likely be ongoing at the 
start of the period and will continue through much of the day due to 
persistent warm advection north of the warm front. While rich 
low-level moisture (characterized by mid-upper 60s f dewpoints) will 
spread slowly northward through the day south of the boundary, 
widespread cloudiness and only modest midlevel lapse rates will tend 
to limit instability, with MLCAPE likely remaining in the 500-1000 
j/kg range across the warm sector. With the primary upper system and 
associated large-scale ascent remaining well to the west during the 
day, the greatest coverage of convection is expected to remain north 
of the boundary, though there will be some potential for a few 
surface-based storms during the afternoon across portions of 
central/southern MS and perhaps northern la, with an attendant risk 
of marginally severe hail and locally damaging wind. While a brief 
tornado cannot be ruled out with any cell that interacts with the 
surface boundary, the potential for substantial surface-based 
development appears too limited at this time to introduce tornado 
probabilities. 


Elevated convection from southeast Arkansas into northern MS may also pose 
some severe risk, especially later tonight when somewhat steeper 
midlevel lapse rates begin to move in from the west as the upper 
trough approaches and the surface boundary gradually moves 
northward. 


..arklatex region late tonight... 
As the primary shortwave moves into the Southern Plains late in the 
period, elevated storms may develop across portions of eastern OK/Texas 
into the arklatex by early Saturday morning. Steep midlevel lapse 
rates and sufficient effective shear will support a conditional risk 
of hail and perhaps locally damaging wind with the strongest cells, 
though the coverage and southward extent of deep convection across 
the region prior to the end of the period at 12z remains uncertain 
at this time. 


.Dean/squitieri.. 02/22/2019 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 212340 
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Mesoscale discussion 0119 
National Weather Service Storm Prediction Center Norman OK 
0540 PM CST Thu Feb 21 2019 


Areas affected...portions of central Alabama into central Georgia 


Concerning...severe potential...watch unlikely 


Valid 212340z - 220145z 


Probability of watch issuance...5 percent 


Summary...risk for a brief tornado associated with low-topped 
convection will exist over the next few hours. Watch issuance is 
not expected. 


Discussion...latest radar continues to show generally 
weak/low-topped convection -- producing little in the way of 
lightning -- across portions of Alabama and Georgia. Ample 
low-topped cape and sufficient shear for storm rotation exists 
across this region, near a weak central Alabama frontal wave and the 
associated/eastward-extending warm front. However, the larger-scale 
environment remains generally unsupportive of stronger/more 
organized convection, with short-wave ridging aloft to gradually 
increase across the region tonight. 


However, a few stronger cells near the aforementioned warm front 
have exhibited organization/low-level rotation over the past hour or 
so; specifically, a cell which is exiting northeast Harris County Georgia 
and moving into southern Meriwether County has exhibited sustained 
low-level rotation and appears capable of producing a weak tornado 
as it interacts with low-level vorticity in the vicinity of the 
surface warm front. 


Though a few additional cells may also follow a similar evolution 
this evening, overall risk is expected to remain limited/local -- 
and thus watch issuance is not anticipated. 


.Goss.. 02/21/2019 


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


Attention...WFO...chs...cae...ffc...bmx...mob... 


Latitude...Lon 33308294 32938259 32798198 32538295 32678388 32468497 
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