U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 181731 
Storm Prediction Center ac 181730 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1130 am CST Tue Dec 18 2018 

Valid 191200z - 201200z 

..no severe thunderstorm areas forecast... 

isolated to scattered thunderstorms are forecast Wednesday from East 
Texas to the central Gulf Coast and the western/southern Florida 
Peninsula, but severe thunderstorms appear unlikely. 

..synopsis and discussion... 
A northern and southern-stream shortwave trough will phase over the 
plains and MS valley on Wednesday, with a highly amplified upper 
trough expected to develop late in the period as a result. Low-level 
moisture return across the northern Gulf of Mexico and adjacent 
central Gulf Coast will occur as a southerly low-level jet 
strengthens Wednesday afternoon/evening. But, a prior frontal 
intrusion has shunted a higher Theta-E airmass well south into the 
Gulf of Mexico per surface observations and visible satellite, and 
substantial modification of the stable near-surface layer will be 
needed to support surface-based thunderstorms. This potential 
appears unlikely for coastal areas of la/MS/al and the Florida Panhandle 
based on latest NAM and rap forecast soundings, which suggest only 
upper 50s to low 60s surface dewpoints will advance slightly inland 
through the period. But, at least isolated thunderstorms should 
develop across this region, and farther inland for a greater portion 
of the southeast, as the low-level jet strengthens and weak elevated 
instability develops. Isolated thunderstorms may also form Wednesday 
afternoon along the middle/Upper Texas coast as mid-level temperatures 
cool beneath the upper trough. Although some instability will be 
present given steepening mid-level lapse rates, gradually decreasing 
shear as stronger mid-level winds shift eastward should preclude an 
organized severe threat. 

A surface low is forecast to develop eastward along/near the central 
Gulf Coast Wednesday night, and substantial thunderstorm development 
appears likely over the central Gulf of Mexico overnight along and 
ahead of an attendant cold front. This convection should organize 
into a line as it moves to the eastern Gulf of Mexico by the end of 
the period, but latest guidance continues to indicate these 
thunderstorms will likely remain offshore the Florida Gulf Coast until 
after 12z Thursday (into day 3). Still, a few pre-frontal 
thunderstorms could develop across the western/southern Florida Peninsula 
overnight as low-level warm air advection gradually increases, but 
generally weak instability should limit the severe potential with 
this activity. 

..maximum risk by hazard... 
Tornado: <2% - none 
wind: <5% - none 
hail: <5% - none 

.Gleason.. 12/18/2018