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    Day 2 Outlook >
Sep 28, 2021 1630 UTC Day 1 Convective Outlook
Updated: Tue Sep 28 16:29:45 UTC 2021 (Print Version | 20210928 1630Z Day 1 shapefile | 20210928 1630Z Day 1 KML)
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 Forecast Discussion
   SPC AC 281629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Tue Sep 28 2021

   Valid 281630Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING ACROSS THE MID-ATLANTIC...

   ...SUMMARY...
   Strong to severe gusts and hail are possible this afternoon and
   evening across parts of the Mid-Atlantic region.

   ...Mid-Atlantic this afternoon/evening...
   An initial midlevel shortwave trough near the PA/MD border will move
   east-southeastward to the Mid-Atlantic coastline by mid afternoon,
   as part of larger-scale trough amplification over the Northeast (in
   response to upstream height rises over the northern Plains).  The
   timing of the lead wave is ahead of the primary diurnal cycle, and
   additional storm development late this afternoon/evening will likely
   depend on lift along the cold front which will move southeastward
   from PA into the Mid-Atlantic by this evening.  In the wake of
   morning convection with the lead shortwave trough, gradual
   moistening and surface heating in cloud breaks ahead of the surface
   front will contribute to MLCAPE of 1000-1500 J/kg by late afternoon
   from VA into the Delmarva/southern NJ.  The moderate buoyancy and
   effective bulk shear of 25-35 kt will support a mix of multicell
   clusters and isolated supercells.  The strongest storms will be
   capable of producing damaging gusts given some storm organization
   with DCAPE near 750 J/kg and 30-40 kt midlevel flow for downward
   momentum transfer.  Midlevel lapse rates near 8 C/km and relatively
   cool midlevel temperatures will also support a threat for occasional
   large hail.

   ...Southern Plains this afternoon/evening...
   A dryline will establish this afternoon along the lee trough from
   near the western OK border to the Edwards Plateau, east of a weak
   midlevel trough over the southern Rockies.  Boundary-layer dewpoints
   increasing into the 60s from south-to-north and strong surface
   heating/mixing will support thunderstorm development along the
   dryline this afternoon/evening from TX into southwest OK.  MLCAPE of
   1500-2000 J/kg and effective bulk shear up to 30 kt will favor a mix
   of multicell clusters and transient supercell structures, with an
   attendant threat for isolated large hail and outflow gusts of 50-60
   mph given steep low-level lapse rates and DCAPE .

   ..Thompson/Bentley.. 09/28/2021

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z

        
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Page last modified: September 28, 2021
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