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Feb 21, 2017 0830 UTC Day 3 Severe Thunderstorm Outlook
Updated: Tue Feb 21 08:21:06 UTC 2017 (Print Version | 20170221 0830Z Day 3 shapefile | 20170221 0830Z Day 3 KML)
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 Forecast Discussion
   SPC AC 210821

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0221 AM CST Tue Feb 21 2017

   Valid 231200Z - 241200Z


   Isolated thunderstorms are forecast across portions of the Midwest
   primarily after sunset Thursday night into early Friday morning.  A
   few storms are possible along the east coast of Florida.

   A large-scale mid-level trough will feature a broad belt of strong
   cyclonic flow moving through its base from the Desert Southwest
   through the central and southern Great Plains and into the Midwest
   on Thursday.  A shortwave disturbance is forecast to move from the
   central Rockies into IA by early Friday morning.  In the low levels,
   a surface low will develop northeastward from the central High
   Plains into the middle MS Valley coincident with the aforementioned
   mid-level impulse.  A warm front will extend eastward from the low
   while a cold front moves southeast across KS and much of OK. 
   Elsewhere, a weak mid-level low will slowly meander to the east of
   the FL peninsula.

   ...middle MS Valley...
   Marginal low-level moisture over the Mid South and lower MS Valley
   will advect northward during the day within the warm conveyer of the
   central U.S. cyclone.  Models suggest dewpoints ranging from 54-58
   degrees F will reach the lower MO Valley and middle MS Valley region
   by early evening.  A southwesterly low level jet is forecast to
   strengthen to 50+ kt after dark across MO/IL with a corresponding
   increase in isentropic ascent.  Showers and isolated thunderstorms
   are forecast to develop primarily on and north of the warm front.  A
   cap will likely limit storm development southward over the Ozarks. 
   Although models show strong shear and marginally unstable profiles,
   notable differences still exist amongst medium-range models on the
   evolution of a mid-level vorticity maximum and surface low track
   over the Midwest.  Given the model variability and uncertainty
   regarding convective evolution late in the Day 3 period, will defer
   to later outlooks about the possible inclusion of low-severe
   probabilities over a portion of this region.

   ..Smith.. 02/21/2017



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