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Dec 18, 2018 1730 UTC Day 2 Convective Outlook
Updated: Tue Dec 18 17:30:20 UTC 2018 (Print Version | 20181218 1730Z Day 2 shapefile | 20181218 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 181730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 AM CST Tue Dec 18 2018

   Valid 191200Z - 201200Z


   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 FL 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 TX 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 FL Gulf Coast until
   after 12Z Thursday (into Day 3). Still, a few pre-frontal
   thunderstorms could develop across the western/southern FL Peninsula
   overnight as low-level warm air advection gradually increases, but
   generally weak instability should limit the severe potential with
   this activity.

   Tornado:  <2%     - None
   Wind:     <5%     - None
   Hail:     <5%     - None

   ..Gleason.. 12/18/2018



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