U.S. Severe Weather Forecast (Convective Outlook)

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Storm Prediction Center ac 140600 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1200 am CST Fri Dec 14 2018 


Valid 141200z - 151200z 


..there is a slight risk of severe thunderstorms across portions of 
northern/central Florida and far southeastern Georgia... 


... 
Isolated severe thunderstorms will be possible from northern/central 
Florida into southeastern Georgia and the coastal Carolinas today 
into tonight. Strong to locally damaging winds should be the main 
threat. 


... 
An upper low centered over East Texas will move northeastward to the Tennessee 
Valley through the period. A related strong 80-100+ kt 
mid/upper-level jet will overspread much of the southeast later 
today. A 40-50 kt southerly low-level jet initially over the Florida 
Panhandle should shift eastward over northern Florida into southeastern 
Georgia and the eastern Carolinas, which will bring increasing low-level 
moisture to these areas through the day. At the surface, an occluded 
low will develop northeastward to the Tennessee Valley in tandem with the 
upper low while continuing to slowly weaken. A secondary surface low 
should form near the Florida Panhandle by this evening and then track 
northeastward along a coastal front across the eastern Carolinas 
through the end of the period. 


..northern/central Florida into southeastern Georgia... 
A pre-frontal line of thunderstorms will likely be ongoing at the 
start of the period over the eastern Gulf of Mexico and perhaps 
extending into parts of the Florida Panhandle. The airmass ahead of these 
storms across northern/should slowly destabilize as the previously 
mentioned low-level jet brings an airmass characterized by mid to 
upper 60s surface dewpoints northward. Even so, limited diurnal 
heating owing to widespread cloudiness and weak mid-level lapse 
rates should temper instability late this morning into the 
afternoon, with MLCAPE of 500-1000 j/kg probable. Deep-layer shear 
will increase to around 35-45 kt across this region by the 
afternoon, which will support continued organization of the 
convective line as it moves eastward across the northern/central Florida 
Peninsula. Isolated strong to damaging winds will likely be the 
primary threat given the linear storm Mode. A tornado or two may 
also occur with circulations embedded within the line as strong flow 
in the 0-3 km layer supports enlarged low-level hodographs. 


..eastern Carolinas... 
Strengthening southerly low-level winds by this evening will 
transport greater low-level moisture over the coastal Carolinas, 
with the potential for near-surface-based thunderstorms likewise 
increasing as surface dewpoints reach into the mid to perhaps upper 
60s. Some threat for isolated strong/gusty winds and perhaps a 
tornado may exist tonight into early Saturday morning, mainly 
along/near the coast associated with the low-level jet and increased 
low-level shear. A relatively greater potential for surface-based 
thunderstorms may exist across far eastern NC the last few hours of 
the period (08-12z), with some model guidance showing greater 
instability across this region. Uncertainty regarding storm coverage 
and the realization of this instability limits confidence in any 
more than marginal probabilities for severe thunderstorms at this 
time. 


..mid-south into MS/al... 
Cold mid-level temperatures and residual moisture wrapping around 
the upper low should act to increase elevated instability over the 
mid-south and vicinity today. Isolated to perhaps widely scattered 
thunderstorms should be ongoing this morning across northern la into 
southern AR, with additional activity developing later this 
afternoon across western Tennessee/Kentucky and northern MS. Forecast soundings 
show wind profiles will likely not be favorable for organized severe 
thunderstorms. But, some storms could produce small hail owing to 
steep mid-level lapse rates. 


Farther east into al, stronger mid/upper-level winds are forecast 
this afternoon, and a pocket of weak instability (mlcape around 500 
j/kg) should develop amidst surface dewpoints in the upper 50s/lower 
60s ahead of a cold front. The forecast environment would 
conditionally support at least some severe potential, but convective 
coverage will likely remain sparse owing to the filling upper low 
and weakening surface low. Have not included marginal probabilities 
due to uncertainty regarding storm initiation/coverage. 


.Gleason/nauslar.. 12/14/2018 


$$ 




Mesoscale Discussion


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Storm Prediction Center mesoscale discussion 140012 
flz000-alz000-140115- 


Mesoscale discussion 1708 
National Weather Service Storm Prediction Center Norman OK 
0612 PM CST Thu Dec 13 2018 


Areas affected...the barrier islands of southern Alabama and near the 
Florida/Alabama border 


Concerning...severe potential...watch unlikely 


Valid 140012z - 140115z 


Probability of watch issuance...5 percent 


Summary...several weak supercells will approach the barrier islands 
south of Mobile Bay and near the Florida/Alabama border. Cool/stable 
conditions in the low levels will limit the brief/weak tornado risk. 


Discussion...recent surface analysis places a warm front roughly 40 
nm south of Alabama barrier islands. Conditions south of the warm front 
are hospitable to weak surface-based cape (200-500 j/kg) whereas 
north of the boundary SBCAPE is nil. The kmob VAD shows a strongly 
veering wind profile supporting storm rotation. Several updrafts in 
the shelf waters south of the Alabama coast have acquired supercell 
rotation during the past 1-2 hours. 


The warm front is forecast to very slowly advance north during the 
evening and approach the coast. As a result, a couple of weak 
mesocyclones may move towards or affect the immediate coast. 
However, given the poor low-level lapse rates acting as a limiting 
factor, it seems unlikely a brief/weak tornado would move onshore. 
The immediate coastal areas of Alabama and the western Florida Panhandle will 
continue to be monitored. 


.Smith/Edwards.. 12/14/2018 


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


Attention...WFO...mob... 


Latitude...Lon 29918834 30248807 30398710 29978700 29918834