SPC AC 200523

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1223 AM CDT Fri Sep 20 2024

   Valid 211200Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   EASTERN NEW MEXICO AND WESTERN TEXAS...

   ...SUMMARY...
   Isolated severe thunderstorms are possible on Saturday afternoon to
   early evening in New Mexico and the southern High Plains, the mid
   Missouri Valley to upper Mississippi Valley, and central
   Appalachians region.

   ...Southern High Plains vicinity...

   A southern stream upper low and attendant trough will progress east
   across the Four Corners and southern Rockies on Saturday. An area of
   enhanced southwesterly flow aloft associated with the ejecting
   trough will become oriented over eastern NM into the OK/TX
   Panhandles by 00z/Sun. While strong heating will result in some
   boundary layer mixing, south/southeasterly low-level flow will
   result in persistent theta-e advection, and dewpoints from the upper
   50s to low 60s F are expected. Steepening midlevel lapse rates will
   contribute to modest destabilization, with 1000-1500 J/kg MLCAPE
   forecast across parts of eastern NM into the TX Panhandle/South
   Plains vicinity. Vertically veering wind profiles amid strengthening
   midlevel flow will support isolated supercell thunderstorms. Large
   hail and sporadic strong/severe gusts are possible. Given increasing
   consistency in forecast guidance, a Slight risk (level 2 of 5) has
   been included for parts of the eastern NM Plains into west Texas.

   Additional strong storms are possible to the north and west across
   northeast NM into south-central CO beneath the core of mid/upper
   low. Instability will be weaker across this area, but isolated
   strong gusts and marginal hail will still be possible with the
   strongest storms. 

   ...Western PA into northern/central VA...

   A low-amplitude mid/upper shortwave trough is forecast to move
   across the Northeast on Saturday. Northwesterly deep-layer flow will
   overspread the Upper OH Valley toward the Mid-Atlantic coast. A
   corridor of low to mid 60s F dewpoints and pockets of stronger
   heating will support weak destabilization. Modest vertical shear
   (around 20-25 kt effective shear) will aid in at least transient
   organized updrafts. Elongated/straight hodographs and cool
   temperatures aloft suggest marginally severe hail will be possible
   with the stronger cells. Locally strong gusts also will be possible
   where stronger heating and steepening of low-level lapse rates
   occurs.

   ...Central Plains to Mid-MO/Upper MS Valley...

   The forecast for this region remains quite uncertain for Saturday.
   Most guidance depicts some degree of convection ongoing across parts
   of IA/MO Saturday morning. The evolution of this activity will
   impact how the airmass destabilizes/recovers late in the afternoon
   across the region. Nevertheless, large-scale ascent will increase
   over the Upper Midwest as a northern stream upper trough traverses
   the Canadian Prairies and the international border vicinity.
   Southerly low-level flow will maintain 60s dewpoints ahead of a cold
   front tracking southeast across MN and the Mid-MO/Upper MS Valley
   from late afternoon into the evening. Isolated strong to severe
   thunderstorms producing hail and gusty winds will be possible, but
   the overall risk remains uncertain.

   ..Leitman.. 09/20/2024

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