U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 230545 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1145 PM CST Thu Feb 22 2018 


Valid 231200z - 241200z 


..there is a marginal risk of severe thunderstorms mainly late 
tonight across northern Texas and adjacent portions of southern 
Oklahoma... 


... 
Strong thunderstorms are possible across northern Texas today 
through tonight. A couple may be accompanied by some risk for 
severe hail, particularly late tonight. 


... 
Although some weakening of the high center off the South Atlantic 
coast may be underway, subtropical ridging appears likely to remain 
prominent across much of the southeast through this period. 
Upstream, models indicate that a vigorous short wave trough (now 
digging near the southern Sierra nevada) will remain progressive and 
maintain considerable strength, pivoting across The Four Corners 
region toward the Central Plains, as another short wave trough digs 
into the Pacific northwest. Forcing associated with the lead 
impulse may support the initiation of cyclogenesis within a 
deepening Lee surface trough across the southern High Plains by 12z 
Saturday. There are discrepancies among the models concerning this 
process, probably at least in part due to differences in the erosion 
of lingering cold surface ridging now present across the Southern 
Plains. However, the primary initial surface low probably will form 
across parts of southeast Colorado/northeast New Mexico into the 
Texas/Oklahoma Panhandle region, while a secondary low forms by late 
tonight along a residual frontal zone across northern Texas, 
probably across the Texas Big Country. As this occurs, substantive 
boundary layer modification and moistening is expected across much 
of southeastern through central Texas. 


..lower Mississippi Valley... 
While elevated moisture return continues on southerly return flow 
above the residual shallow cold surface-based air mass across much 
of the Southern Plains, a warm and moist boundary layer air mass is 
already present across portions of the Upper Texas coast and Sabine 
valley, east northeastward through parts of central and southern 
Louisiana. Models suggest some north/northeastward advection of 
this air mass is possible today, with surface heating contributing 
to destabilization and potential for scattered afternoon and evening 
thunderstorm development across Louisiana and southern/central 
Mississippi. While modest southwesterly mid-level flow (30-40 kt at 
500 mb) could enhance convection, low-level flow and hodographs are 
expected to remain rather modest in strength. With thermodynamic 
profiles only supporting weak to modest cape, severe storm 
probabilities still seem less than 5 percent. 


..Texas Big Country into the Red River valley... 
Thunderstorm activity may be ongoing or in the process of increasing 
in coverage at 12z this morning, in response to lower/mid 
tropospheric warm advection above the cold surface-based air. In 
the presence of modestly steep mid-level lapse rates, some risk for 
marginally severe hail may not be out of the question, and could 
continue through the day, as periodic scattered thunderstorm 
redevelopment remains focused across the region, on the northern 
periphery of capping elevated mixed layer air. Further steepening 
of mid-level lapse rates, increasing mid/upper forcing for ascent, 
and strengthening deep layer wind fields and shear with the impulse 
emerging from the southwest may contribute to somewhat better 
potential for convection capable of producing severe hail late 
tonight (toward 12z saturday). 


.Kerr/leitman.. 02/23/2018 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 221211 
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Mesoscale discussion 0086 
National Weather Service Storm Prediction Center Norman OK 
0611 am CST Thu Feb 22 2018 


Areas affected...portions of central and northern Texas and into 
parts of southern Oklahoma 


Concerning...severe potential...watch unlikely 


Valid 221211z - 221445z 


Probability of watch issuance...5 percent 


Summary...an increase in convection -- including potential for 
marginally severe hail as well as local ice accumulation due to 
freezing rain -- is ongoing across portions of central and northern 
Texas. Ww is unlikely. 


Discussion...latest radar loop shows an increase in elevated showers 
and thunderstorms ongoing across portions of Texas -- particularly 
over The Hill Country and surrounding areas. The storms are 
occurring as large-scale ascent increases across the Southern Plains 
in association with a short-wave trough moving northeastward across 
eastern New Mexico, and within a zone of ample (at least 1000 j/kg) 
cape, elevated atop a layer of near -- or below -- freezing 
temperatures. 


Given the aforementioned characteristics of the thermodynamic 
profile, areas of ice accumulation will be possible with briefly 
heavy downpours. Additionally, the degree of cape combined with 
background cloud-layer shear around 50 kt suggests that a few 
organized/possibly rotating storms will be possible, with local risk 
for marginally severe hail with the strongest cells. 


With time, expect this area of showers and storms to spread 
northeastward across North Texas and into Oklahoma, where the lack 
of better cape should mitigate any hail risk but where freezing rain 
-- and thus some ice accumulation -- will still be a concern. 


.Goss/guyer.. 02/22/2018 


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


Attention...WFO...fwd...oun...sjt...lub...maf... 


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