U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 140054 
Storm Prediction Center ac 140052 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0652 PM CST Thu Dec 13 2018 

Valid 140100z - 141200z 

..there is a marginal risk of severe thunderstorms across parts of 
the central Gulf Coast/western Florida Panhandle... 

Isolated strong to severe thunderstorms may occur over parts of the 
central Gulf Coast/Florida Panhandle tonight. 

The potential for isolated strong to severe thunderstorms across the 
arklatex appears to have diminished this evening with the loss of 
daytime heating and meager low-level moisture limiting instability. 
Have therefore removed the marginal risk for this region. 

Additional convective development may occur across northern la into 
southern Arkansas late in the period (09-12z) as a surface low occludes 
and strong large-scale forcing associated with an upper low over 
central/East Texas overspreads this region. Even though 700-500 mb 
lapse rates should steepen as mid-level temperatures decrease 
beneath the upper low, weak effective bulk shear and poor low-level 
lapse rates will likely preclude a meaningful severe threat. 

..al/Florida Gulf Coast... 
00z surface analysis indicates a warm front extending across 
southern la to just offshore the coast of MS/Alabama and the western Florida 
Panhandle. As a surface cyclone occludes over East Texas/western la 
overnight, the warm front should slowly advance northward along the 
central Gulf Coast. Even so, surface dewpoints moving onshore will 
probably remain in the low to mid 60s through 12z, and only weak 
surface-based instability is expected. Strong shear in the 0-3 km 
layer associated with a 40-50 kt southerly low-level jet will likely 
support updraft rotation with low-topped thunderstorms, and the 
threat for a tornado or two occurring along/near the coast through 
early Friday remains sufficient to justify a marginal risk. Isolated 
strong to locally damaging winds could also occur. 

For more information on the severe threat this evening along the 
immediate coast/barrier islands of Alabama and the far western Florida 
Panhandle, see mesoscale discussion 1708. 

.Gleason.. 12/14/2018 


Mesoscale Discussion

acus11 kwns 140012 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 140012 

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... 


Latitude...Lon 29918834 30248807 30398710 29978700 29918834