U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 280608 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0108 am CDT Tue Mar 28 2017 


Valid 281200z - 291200z 


..there is an enhanced risk of severe thunderstorms across parts of 
central and southern Oklahoma across North Texas into the Concho 
Valley area... 


..there is a slight risk of severe thunderstorms including large 
portions of Oklahoma and Texas... 


..there is a marginal risk of severe thunderstorms across the 
Southern Plains... 


..there is a marginal risk of severe thunderstorms over parts of 
Virginia and North Carolina...and vicinity... 


... 
Scattered to numerous severe storms are forecast Tuesday and Tuesday 
night across the Southern Plains. A few strong to severe storms are 
also possible over parts of the mid-Atlantic region. 


... 
A large mid- and upper-level trough/low initially centered over The 
Four Corners states will move eastward across the southern rockies 
during the day, gradually emerging into western portions of the 
Southern Plains through the afternoon and evening. Meanwhile, a 
much weaker short-wave trough crossing the central Appalachians and 
vicinity early in the period will shift toward/off the middle and 
southern Atlantic coasts through the daytime hours. 


At the surface, a weak low will cross the Virginia/North Carolina 
vicinity through the day. Over the Southern Plains, a low is 
forecast to move out of eastern New Mexico into/across the High 
Plains of Texas through the afternoon and evening. A dryline will 
mix very slowly eastward across West Texas through the day -- and 
should be overtaken by a faster-moving Pacific cold front during the 
evening/overnight. Meanwhile, a west-to-east warm front is forecast 
to be lifting gradually northward across Texas through the day, 
likely shifting northward into Oklahoma during the evening/overnight 
as low-level flow strengthens. This surface system and the 
associated upper low/trough will support widespread convection and 
enhanced severe weather risk across much of Texas and northward into 
Oklahoma -- particularly during the late afternoon and evening 
hours. 


..the Southern Plains... 
Persistent southerly low-level flow ahead of the advancing storm 
system will allow moistening of the boundary layer through the day, 
along with gradual northward shift of the west-to-east warm front 
across Texas with time. As a dryline mixes slowly eastward across 
the South Plains and transpecos region, initiation of storms is 
forecast by mid to late afternoon -- both along the dryline and 
perhaps, in a more isolated manner, northwestward into portions of 
the Texas Panhandle. 


As the storms initiate within a moderately unstable environment, 
strengthening flow aloft -- veering from southeasterly at the 
surface to south-southwesterly aloft -- updrafts will acquire 
rotation and become capable of producing very large hail and locally 
damaging gusts. Additionally, initial cellular Mode suggests 
potential for a few tornadoes -- particularly across western North 
Texas where a strong tornado will be possible. 


As storms mature, upscale growth into lines (with bowing segments) 
is expected -- due to both very strong large-scale ascent and 
meridional flow aloft roughly parallel to the dryline/developing 
cells. The band of storms should accelerate across North Texas and 
into southern/central Oklahoma during the evening, along with 
attendant risks for damaging winds and hail, and possibly an 
additional tornado or two. 


Meanwhile, additional storm development is expected during the 
evening farther southwest along the advancing Pacific front. As 
this front merges with the dryline, the band of storms may elongate 
both northward and southward, with northern portions of the band 
possibly bringing a second round of storms/possible severe weather 
to parts of Oklahoma and North Texas. Farther south, the convection 
should advance east across much of central Texas through the evening 
and overnight along with risk for hail and locally damaging winds. 


..the Virginia/North Carolina vicinity... 
Multiple rounds of showers and isolated thunderstorms are forecast 
to move across the Virginia/NC vicinity during the first half of the 
period, as the upper system moves across the area. Due to 
clouds/ongoing precipitation as ascent spreads eastward across the 
area relatively early in the diurnal cycle, destabilization is 
likely to remain somewhat subdued. This -- in conjunction with the 
relative weakness of the system -- suggests overall severe risk 
should remain tempered. As such, will maintain only marginal risk for 
wind/hail with isolated stronger cells at this time. Risk should 
diminish through late afternoon, and end by evening as the system 
moves offshore. 


.Goss/cohen.. 03/28/2017 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 272259 
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Mesoscale discussion 0349 
National Weather Service Storm Prediction Center Norman OK 
0559 PM CDT Mon Mar 27 2017 


Areas affected...parts of western/middle Tennessee and adjacent 
areas 


Concerning...Severe Thunderstorm Watch 89...91... 


Valid 272259z - 280030z 


The severe weather threat for Severe Thunderstorm Watch 89, 91 
continues. 


Summary...the risk mainly for severe hail and strong surface gusts 
is expected to continue with storms overspreading middle Tennessee 
into/through the 7-10 PM CDT time frame. 


Discussion...in the wake of generally weakening, loosely organized 
convective development now spreading toward the central/southern 
Appalachians, an area of enhanced low-level warm advection is 
maintaining vigorous thunderstorm activity near/east of the 
Interstate 40 corridor of western into middle Tennessee. Forcing 
associated with the remnants of a compact mid-level closed low 
likely is augmenting ascent and associated convection, which is 
expected to continue to spread eastward across middle Tennessee 
into/through the 00-03z time frame. 


Inflow of relatively moist low-level air into the vicinity of this 
activity, beneath a lingering area of steep mid-level lapse rates is 
probably contributing to moderately large cape. This may be mostly 
based above a relatively stable surface-based air mass, but, in the 
presence of strong vertical shear, supercells will remain possible, 
with upscale growth into a small organizing convective system 
possible through mid/late evening. While an additional isolated 
tornado may not be out of the question, the risk for severe hail and 
strong surface gusts seems more prominent. 


.Kerr.. 03/27/2017 


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


Attention...WFO...mrx...lmk...ohx...hun...pah...Meg... 


Latitude...Lon 36648735 36848646 36658534 35898499 34978634 34768747 
34928859 35138904 35948841 36648735