SPC AC 241951

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0151 PM CST Tue Nov 24 2020

   Valid 242000Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHEAST
   TX PANHANDLE INTO NORTHEAST OK...

   ...SUMMARY...
   Severe thunderstorms are expected from the Texas Panhandle into
   Oklahoma through this evening. More isolated severe storms are
   possible overnight from northeast Texas into Arkansas.  Large hail
   and damaging winds will be the main threats, along with a couple of
   tornadoes.

   ...20z Update - Southern Plains/Ark-La-Tex...

   Only minor adjustment have been made to the 10% general thunderstorm
   line across parts of the Plains based on latest trends and CAMs
   guidance. Otherwise, the ongoing outlook is on track. Strong
   thunderstorms have developed across parts of the OK/TX Panhandles
   this afternoon where temperatures have warmed into the 60s and
   MLCAPE has increased to around 500 J/kg near and east of current
   convection. Additional storms are expected to develop with time as
   the surface low and cold front develop eastward toward western OK
   over the next couple of hours. Large hail, damaging gusts, and a
   tornado or two still appear possible through this evening across the
   Slight risk area. Most recently, 1 inch hail has been reported with
   storms in Beaver County, OK. For more details, reference MCD 1807.

   ..Leitman.. 11/24/2020

   .PREV DISCUSSION... /ISSUED 1027 AM CST Tue Nov 24 2020/

   ...Parts of the southern Plains to the Ark-La-Tex through tonight...

   A midlevel shortwave trough over NM this morning will progress
   eastward to northwest TX and western OK by late evening, and then
   continue northeastward to MO/AR by the end of the period.  The
   midlevel trough will be preceded by a surface cyclone that will
   develop eastward from the TX Panhandle this afternoon to western OK
   this evening, and then northeastward to MO overnight.  A narrow
   corridor of mid-upper 50s boundary-layer dewpoints will return
   northward to the east of a dryline, where a few cloud breaks could
   allow pockets of surface heating as far north as west central or
   northwest OK by mid-late afternoon.  

   Storm development appears probable by mid afternoon in the TX
   Panhandle near the triple point, and storms will subsequently spread
   eastward into west central and northwest OK late this
   afternoon/evening, generally along and north of I-40.  Deep-layer
   shear will support supercells, but rather modest low-level shear and
   substantial forcing for ascent in the left-exit region of the
   mid-upper jet suggest that some upscale growth into clusters or line
   segments is also probable.  Thus, there will be some threat for a
   tornado or two relatively early in the convective evolution across
   northwest OK, in proximity to the surface boundaries and where
   low-level lapse rates/CAPE will be largest.  Isolated very large
   hail will be a threat with supercells given steep lapse rates and
   500 mb temperatures colder than -17 C, and damaging winds will
   become more of a concern this evening as convection grows upscale.

   A separate zone of convection is expected overnight from northeast
   TX into southeast OK and western AR, both in pre-frontal warm
   advection and along the cold front as it encounters richer low-level
   moisture and weakening convective inhibition.  Convection will
   likely remain elevated near and north of I-40, with more
   surface-based convection closer to northeast TX.  Vertical shear
   will be strong in this corridor, but there will be a tendency for
   the stronger forcing for ascent to begin passing north of the more
   unstable warm sector late in the period.  Overall, isolated severe
   storms may occur overnight from northeast TX into AR, but it is
   still not clear that a more concentrated severe threat will evolve
   in this corridor, so low severe probabilities will be maintained in
   this update.

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