SPC AC 201727

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 PM CDT Wed Sep 20 2023

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   SOUTHERN OKLAHOMA AND NORTH TEXAS...

   ...SUMMARY...
   Severe thunderstorms producing damaging gusts and hail are possible
   across parts of southern Oklahoma into north Texas Thursday
   afternoon. Isolated strong to severe thunderstorms also are possible
   across parts of the central Plains and the southern High Plains.

   ...Synopsis...

   An upper low and attendant trough will slowly pivot across the
   Pacific Northwest and Intermountain West on Thursday. Ahead of this
   feature, diffluent upper flow will overspread much of the
   central/southern Plains vicinity. Several shortwave impulses are
   forecast to migrate across the Rockies and into the Plains, focusing
   potential for several areas of strong to severe thunderstorms
   Thursday afternoon and evening.

   ...Oklahoma into North Texas Vicinity...

   Morning clouds and possibly showers over parts of the OK/TX
   Panhandles into western/central OK will result limit destabilization
   for much of the period. However, strong heating to the south/east of
   this bubble of inhibition will result in a strong differential
   heating gradient across southern OK. Mid/upper 60s dewpoints and
   modest midlevel lapse rates will aid in moderate destabilization,
   with forecast MLCAPE values near 2000 J/kg. Deep-layer flow will not
   be particularly strong through about 600 mb, before rapidly
   increasing through the top of the cloud-bearing layer. Nevertheless,
   this will support effective shear magnitudes greater than 30 kt and
   organized cells/clusters are expected. Fairly long, straight
   hodographs suggest hail will be possible, though storm mode may
   preclude a more widespread large hail risk. Steep low-level lapse
   rates aided by temperatures warming into the low 90s, with a mixed
   boundary-layer to around 850 mb suggest isolated severe gusts are
   possible, and a small Slight (level 2 of 5) risk has been
   introduced.

   ...Central Plains Vicinity...

   Weak surface low development is forecast near the SD/WY border
   Thursday afternoon. A surface trough will extend southward into
   eastern CO/western KS. East of the surface trough, southeasterly
   low-level flow will transport low 60s dewpoints across portions of
   KS/NE and SD. This will support a band of moderate instability with
   MLCAPE values approaching 2000-2500 J/kg from south-central SD into
   western/central NE and portions of KS. Deep-layer flow is forecast
   to be somewhat modest, especially above around 700 mb. However,
   25-35 kt 850-700 mb flow, and vertically veering wind profiles will
   result in enlarged/curved low-level hodographs. This should support
   a few organized cells/clusters with some risk for hail and strong
   gusts. Some guidance continues to indicate capping in the 850-700
   mb, which could limit coverage and/or longevity of any
   better-organized convection. An outlook upgrade may be needed in
   subsequent outlooks, but confidence remains too low at this time to
   include a Slight (level 2 of 5) risk.

   ...Southern High Plains...

   East/southeast low-level flow to the east of the surface trough will
   maintain generally upper 40s to upper 50s surface dewpoints across
   eastern NM. However, steep midlevel lapse rates and strong heating
   will support a corridor of modest destabilization (MLCAPE around
   1000-1500 J/kg) by afternoon. Vertically veering wind profiles with
   strong speed shear above 700 mb will support effective shear
   magnitudes greater than 40 kt with elongated/straight hodographs
   evident in forecast soundings. A few high-based cells are expected
   during the late afternoon/early evening. Any cells moving through
   the corridor of greater instability will pose a risk for hail given
   forecast shear and steep midlevel lapse rates. Steep low-level lapse
   rates and a deeply mixed boundary layer also will support a few
   strong gusts. Overall coverage is expected to remain limited,
   precluding higher severe probabilities.

   ..Leitman.. 09/20/2023

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