U.S. Severe Weather Forecast (Convective Outlook)

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acus01 kwns 221932 
swody1 
Storm Prediction Center ac 221931 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0131 PM CST Thu Feb 22 2018 


Valid 222000z - 231200z 


..no severe thunderstorm areas forecast... 


... 
clusters of elevated thunderstorms will continue through the period 
from Texas and Oklahoma to parts of the Mississippi and Ohio Valley 
regions. 


Only minor changes to the Texas and California portions of the general 
thunderstorm lines were made. Heating continues across parts of 
northern CA, which may yield isolated weak thunderstorms later this 
afternoon in association with a shortwave trough with very cold 
temperatures aloft. In TX, the west edge of the initial elevated 
storm activity is gradually shifting eastward. However, a few storms 
are possible later tonight near the Rio Grande, moving into central 
Texas where warm advection aloft will increase again. 


Elsewhere, elevated storms should persist across eastern OK into Arkansas 
where lift is strongest. Farther south, surface based instability 
does exist south of a retreating front, but lift does not appear 
sufficient for any marginal severe threat. 


.Jewell.. 02/22/2018 


Previous discussion... /issued 1023 am CST Thu Feb 22 2018/ 


... 
A deep midlevel trough will continue to dig south-southeastward 
along the Pacific coast with an associated low-end thunderstorm 
threat, while a downstream shortwave trough ejects northeastward 
from the southern High Plains to the upper Midwest around the 
northwest periphery of the southwest Atlantic ridge. A slow-moving 
baroclinic zone will persist from eastern Tennessee/Kentucky to the northwest 
Gulf Coast. The vast majority of the convection this forecast 
period will be elevated, rooted above the shallow sloped frontal 
surface from the Southern Plains to the MS/Ohio valleys regions. Most 
of the thunderstorms will be focused in the warm advection zone 
preceding the midlevel trough now ejecting northeastward across 
Texas/OK, though this convection is already progressing away from the 
source region of steeper lapse rates/moisture and larger resultant 
buoyancy. Farther east, thunderstorms will be rooted closer to the 
surface on the immediate cool side of the slow-moving front from la 
to Tennessee. The primary source for lift will be warm advection atop the 
cool air mass, while vertical shear and ascent should remain weak in 
the warm sector. As such, severe storms appear unlikely. 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 221211 
okz000-txz000-221445- 


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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