U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 221626 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1126 am CDT sun Oct 22 2017 


Valid 221630z - 231200z 


..there is a marginal risk of severe thunderstorms this afternoon 
across southeast la...and through tonight into southern and central 
Alabama... 


..there is a marginal risk of severe thunderstorms this 
afternoon/evening from northern Montana to northwestern ND... 


... 
Isolated damaging gusts will be possible this afternoon across 
southeast Louisiana, while isolated damaging gusts and a brief 
tornado or two will be possible through tonight into southern and 
central Alabama. Isolated strong/damaging gusts will be possible 
this afternoon and evening across northern Montana and northwestern 
North Dakota. 


..southeast la today and southern Alabama through tonight... 
A midlevel trough approaching the MS valley could briefly evolve 
into a closed low over the mid south, prior to beginning to 
accelerate north-northeastward as a more open wave Monday. An 
associated surface cold front will continue eastward across 
la/MS/al, to the south of weak cyclogenesis across the Tennessee and lower 
Ohio valleys. Outflow from overnight convection has become the 
effective cold front across la/MS this morning, and this boundary 
will continue to move eastward/southeastward through the day. 
Farther east, a zone of low-level warm advection, on the nose of the 
Richer low-level moisture and highest pw, has focused convection 
from the MS coast into southwest Alabama. Several storms with supercell 
structures have been observed, per the Mobile vwp hodograph, though 
the storms thus far have weakened while encountering a more stable 
environment inland. 


Some low-end damaging wind potential will accompany the outflow 
across southeast la today, and there will continue to be a low-end 
threat for rotating storms and a brief tornado along the southeast 
MS and southwest Alabama coasts. Gradual destabilization is underway to 
the east of the ongoing warm advection storms, and it appears there 
will be enough inland warming and moistening to support some 
expansion of the marginal risk area in Alabama through tonight. 


..northern Montana/northwestern ND this afternoon/evening... 
A strong mid-upper jet accompanying a shortwave trough will progress 
eastward from the northern rockies to the northern High Plains, 
before turning southeastward around the northeastern periphery of a 
ridge along the Pacific coast. Surface heating and residual 
low-level moisture should be sufficient to support very weak 
surface-based cape this afternoon/evening from northern Montana into 
northwestern ND, along and immediately south of the path of the 
associated surface cyclone. Given steepening low-level lapse rates 
with the weak buoyancy, some low-topped convection could result in 
downward transport of high-momentum flow just above the surface. 


.Thompson/leitman.. 10/22/2017 


$$ 

Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 221900 
gaz000-flz000-alz000-222030- 


Mesoscale discussion 1736 
National Weather Service Storm Prediction Center Norman OK 
0200 PM CDT sun Oct 22 2017 


Areas affected...portions of southern Alabama and th western Florida 
Panhandle 


Concerning...severe potential...watch unlikely 


Valid 221900z - 222030z 


Probability of watch issuance...20 percent 


Summary...a few strong wind gusts and a brief/weak tornado or two 
may occur across southern Alabama into the western Florida Panhandle 
through the afternoon and early evening. A watch is not expected at 
this time. 


Discussion...heating ahead of a cluster of storms currently located 
over southwest Alabama has allowed for weak destabilization (less than 
1000 j/kg) across the Florida Panhandle into southern Alabama. While 
midlevel lapse rates are unremarkable, convection is likely being 
enhanced by an embedded mesoscale convective vortex (noted earlier in the morning over 
southeast ms). Near the apex of the bowing structure over Baldwin 
County, Alabama some stronger wind gusts will be possible as the storm 
cluster tracks east-northeast as low level lapse rates have 
steepened sufficiently. Additionally, a narrow zone of effective srh 
values around 200 m2/s2 will shift northeast across southern Alabama and 
the Florida Panhandle. A few briefly rotating cells have already been 
noted moving inland east of Mobile and this trend should continue as 
the system tracks northeast. Given the overall marginal nature of 
the thermodynamic and kinematic environment and transient/weak 
nature of any rotating cells, a watch is not expected at this time. 


.Leitman/Thompson.. 10/22/2017 


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


Attention...WFO...tae...bmx...mob... 


Latitude...Lon 30048707 30118764 30288797 30888803 31248785 31518752 
32018668 32128597 32108547 31988518 31588504 30878512 
30098554 29888573 30048707