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Feb 20, 2018 1730 UTC Day 2 Convective Outlook
Updated: Tue Feb 20 17:27:45 UTC 2018 (Print Version | 20180220 1730Z Day 2 shapefile | 20180220 1730Z Day 2 KML)
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 Forecast Discussion

   SPC AC 201727

   Day 2 Convective Outlook RESENT 1
   NWS Storm Prediction Center Norman OK
   1127 AM CST Tue Feb 20 2018

   Valid 211200Z - 221200Z


   Showers and embedded thunderstorms are expected from Texas through
   the lower Mississippi Valley to the Ohio Valley Wednesday.
   Marginally severe storms are possible from east Texas into
   Louisiana, with small hail possible into central Texas.

   An amplified large-scale pattern will persist into Wednesday with an
   upper ridge centered over the western Atlantic, and a large upper
   trough across the western CONUS. In between, a broad region of
   strong southwest flow will exist from the southern Plains into
   eastern Canada. Within this area of southwest flow, an intense
   low-amplitude shortwave trough will move from the upper Great Lakes
   into Quebec, with an impressive 200+ kt upper level jet max, with
   generally neutral height tendencies aloft to the southwest, although
   a weak impulse is expected to move across TX.

   At the surface, a cold front will extend from a low in Quebec
   southwestward across the OH/TN Valleys, and across the lower MS
   Valley across southern TX. A moist air mass with 60+ dewpoints will
   exist ahead of the front from TX into the OH Valley, with dewpoints
   near 70 F across coastal TX to the Sabine river. Warm advection in
   the lower levels coupled with lift along and north of the cold front
   will result in thunderstorm activity from TX to OH, the strongest of
   which will exist from TX into LA.

   ...East Texas into Louisiana...
   Moderately strong southwest flow aloft will persist over the area
   along with warm, moist southerly low-level flow. This is expected to
   counteract/stall the front, perhaps resulting in a weak surface wave
   along it. Models are in good agreement depicting a zone of
   thunderstorms developing by late morning through afternoon across
   east TX, continuing into western LA. Low-level shear appears
   marginally supportive of rotating storms should storm mode be
   cellular. However, a large number of storms could have negative
   impacts as far as supercell potential. Any threat is expected to end
   after 00Z as lift from differential divergence tied to the large jet
   max to the north moves away from the area.

   ...Much of central Texas...
   The cold front will continue to drift southward during the day,
   undercutting a moist and marginally unstable air mass and resulting
   in elevated instability. This will be maintained by a broad region
   of warm advection with 20-30 kt southerly 850 mb flow. Lift will
   occur mainly via warm advection, although a storm or two cannot be
   ruled out along the actual front across southern TX, but 0-3 km
   lapse rates will be poor there.  Given cool temperatures aloft and
   sufficient instability, a few storms may be capable of marginal
   hail, but the threat does not appear high enough for a Marginal Risk
   at this time.

   ..Jewell.. 02/20/2018



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