SPC AC 190552

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1252 AM CDT Wed Apr 19 2023

   Valid 191200Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN
   OKLAHOMA...CENTRAL/EASTERN KANSAS...SOUTHEAST NEBRASKA...NORTHWEST
   MISSOURI...AND PARTS OF IOWA...

   ...SUMMARY...
   Severe thunderstorms with the potential for very large hail, a risk
   for a few of tornadoes, and severe gusts will be possible late this
   afternoon into tonight across parts of the central states.

   ...Central/Southern Plains to the Upper Midwest Vicinity...

   A closed upper low is forecast to meander over eastern MT to
   southern SK today/tonight. An upper shortwave trough attendant to
   the low will pivot across the central/southern Rockies and into the
   Plains during the afternoon and into the overnight period. As this
   occurs, increasing southwesterly deep-layer flow will overspread the
   Plains, with a 55-70 kt 500 mb jet developing over KS/NE by 00-03z. 


   An initial surface low is forecast near the southeast NE/northeast
   KS border this morning, before occluding by midday. However, as the
   mid/upper trough begins to eject over the Rockies and into the
   Plains, stronger cyclogenesis will result in a deepening low over
   western KS by late afternoon. This low will lift northeast during
   the evening, with a sharpening dryline extending southward across
   central KS into western OK/TX. Overnight, a cold front will sweep
   southeast across the central/southern Plains. 

   A relative max in severe thunderstorm potential is expected in the
   vicinity of the triple point from central KS into southeast NE where
   the best combination of favorable shear, stronger forcing and
   adequate boundary-layer moisture will reside. Forecast guidance
   still indicates some degree of spread with regard to northward
   moisture return, but dewpoints to at least the low 60s F seem likely
   across central/eastern KS, northeast into the mid-MO Valley
   vicinity. Very steep mid-level lapse rates atop modest
   boundary-layer moisture will promote strong destabilization, and
   convective initiation appears likely near the triple point from
   north-central/northeast KS into southeast NE by 00z. Initial
   supercells capable of very large hail are possible. A few tornadoes
   also will be possible near the surface low and along the warm front
   where low-level vorticity and shear will be enhanced. As a low-level
   jet increases during the evening and the cold front surges
   southeastward across the central Plains, some upscale development
   into a line is possible with an accompanying increase in damaging
   wind potential. This activity should spread northeast into
   IA/southern MN and WI/northern IL overnight with a continued
   wind/hail threat. 

   A more conditional threat is expected with southward extent along
   the dryline into parts of western/central OK, and perhaps as far
   south as western north TX. A sharp dryline will reside across
   western OK with surface dewpoints in the mid 60s possible.
   Large-scale ascent will be weaker with southward extent. However,
   strong heating along the dryline and favorable low-level convergence
   is likely to aid in attempts to overcome moderate capping. If
   capping is overcome, isolated discrete supercells will have a narrow
   window of opportunity to develop across parts of western/central OK.
   While mixing/entrainment of drier air is expected (and may delay
   convective initiation until near/after 00z), ECAPE still indicates
   MLCAPE near/above 2500 J/kg. Furthermore, enlarged low-level
   hodographs becoming elongated above 3 km are forecast. This
   parameter space will be more than sufficient to support potentially
   very large hail (3+ inch diameter). A tornado or two, along with
   damaging gusts also will be possible with any supercell that may
   develop. If cells can become established, severe potential will be
   limited in time/space given expected late initiation timing and
   increasing CINH with eastward extent after 00z.

   ...TX dryline...

   Model guidance currently indicates a paucity of convective potential
   along the dryline over parts of north-central TX southward to the
   Edwards Plateau.  A conditionally very unstable boundary layer and
   deep-layer shear will support supercell potential.  Any storm that
   manages to develop will likely pose a large-hail threat for at least
   an hour or two before this risk diminishes by mid evening.

   ..Leitman/Squitieri.. 04/19/2023

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