SPC AC 180728

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Mon Sep 18 2023

   Valid 201200Z - 211200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms are possible across the
   southern Plains Wednesday afternoon and evening.

   ...Synopsis...
   Embedded perturbations within zonal mid-level flow will de-amplify
   as they move away from the southern Plains, followed by an upper
   ridge impinging on the Plains states by Wednesday afternoon.
   However, amplification of a mid-level trough across the Interior
   West will prompt surface lee troughing and southerly low-level
   moisture return across the Plains states, fostering at least
   scattered thunderstorm potential. Latest guidance consensus suggests
   that adequate buoyancy may develop across the warm sector over
   portions of the southern Plains to support isolated strong to
   potentially severe thunderstorms Wednesday afternoon and evening.

   ...Portions of the southern Plains...
   Scattered thunderstorms are expected to be ongoing across central OK
   into north TX at the start of the period. As the afternoon
   progresses, upper ridging should build over the southern Plains,
   coinciding with weakening of the early-day storms and increased
   surface heating. As surface lee troughing intensifies over the
   southern Plains, 60-65 F surface dewpoints should advect
   northwestward beneath 7-8 C/km mid-level lapse rates, with MLCAPE
   potentially reaching 2000-2500 J/kg by afternoon peak heating.
   Strengthening northwesterly mid to upper flow with the approaching
   upper ridge will contribute to elongated hodographs and 30-40 kts of
   effective bulk shear. Given early day convection and expected height
   rises with the approaching upper ridge, overall confidence in an
   organized round of severe thunderstorms is low. Nonetheless, any
   storm that manages to develop and become sustained in the
   aforementioned kinematic/thermodynamic environment may become
   briefly supercellular, supporting an isolated severe hail/wind risk.

   ...Portions of the northern Plains into the Upper MS Valley...
   Synoptic-scale deep-layer ascent and vertical shear is expected to
   be weak across the northern Plains into the Upper MS Valley,
   limiting convective coverage. However, 7 C/km mid-level lapse rates
   overspreading 55-60 F surface dewpoints along a near-stationary
   surface boundary will boost SBCAPE into the 1000-1500 J/kg range. It
   is not out of the question that a couple of stronger thunderstorms
   could produce some hail/wind approaching severe limits. However,
   confidence in this scenario is too low to warrant severe
   probabilities this outlook.

   ..Squitieri.. 09/18/2023

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