U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 230055 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0655 PM CST Thu Feb 22 2018 


Valid 230100z - 231200z 


..no severe thunderstorm areas forecast... 


... 
a risk for scattered thunderstorm activity continues tonight across 
parts of the Ozark Plateau into the Southern Plains, and perhaps 
northeastward into the lower Ohio Valley. 


..01z outlook update... 
Subtropical ridging centered off the South Atlantic coast remains 
rather strong. Around its northwestern periphery, the large-scale 
flow is generally anticyclonic from the Rio Grande Valley through 
the Ohio Valley and northern mid Atlantic region, though there are a 
number of embedded smaller-scale short wave perturbations. Another 
impulse emanating from the subtropical eastern Pacific may cross the 
lower Rio Grande Valley by late tonight. 


Otherwise, an initial perturbation emerging from positively tilted 
larger-scale troughing over the western U.S. Is forecast to migrate 
from the north Central High plains toward the upper Midwest, as a 
much stronger upstream short wave trough continues to dig near the 
Sierra Nevada into the southern Great Basin/lower Colorado valley. 


Although the track of the lead short wave is well to the west and 
north of a sharp surface frontal zone still stalled across parts of 
the Cumberland Plateau through the lower Mississippi Valley and 
Texas Gulf Coast region, a southerly return flow continues to 
contribute to moistening off the western Gulf of Mexico, and above 
the shallow southern edge of the cold surface-based air mass. This 
is being enhanced across the southeastern plains into the Ozark 
Plateau by a 40-50 kt southwesterly 850 mb speed maximum associated 
with the upper wave, which is contributing to scattered ongoing 
thunderstorm development. As the low-level jet shifts northeastward 
overnight, it appears that associated moistening and destabilization 
could contribute to scattered thunderstorms spreading across parts 
of the middle Mississippi into lower Ohio valleys. 


At the same time, lower/mid tropospheric warm advection is expected 
to persist across much of Texas. Models indicate that this may 
contribute to additional thunderstorm development along the stalled 
leading edge of the deeper cold surge into the Southern Plains, 
across northern Texas by late tonight. Guidance remains suggestive 
that other thunderstorm activity could develop northeast of the 
Mexican plateau into portions of south central Texas. Although the 
Texas convection may coincide with some steepening of lower/mid 
tropospheric lapse rates, it is still not clear that convective 
layer shear and instability will become supportive of the potential 
for much more than generally sub-severe hail in strongest storms. 


.Kerr.. 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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