SPC AC 180600

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Mon Sep 18 2023

   Valid 191200Z - 201200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Scattered severe thunderstorms are possible Tuesday and Tuesday
   night across portions of the southern Great Plains. Large to very
   large hail and severe gusts are the primary hazards.

   ...Synopsis...
   Relatively zonal mid-level flow will overspread the central and
   southern CONUS as an upper trough gradually amplifies across the
   northwestern U.S. tomorrow/Tuesday. However, multiple mid-level
   perturbations embedded within the zonal flow will eject into the
   southern Plains by Tuesday afternoon/evening, supporting pronounced
   lee troughing and some north-northwestward transport of low-level
   moisture. The mid-level perturbations overspreading the moisture
   will promote deep-layer ascent, supporting scattered strong to
   severe thunderstorms over the southern Plains.

   ...Portions of the Southern Plains...
   By afternoon, the approach of a mid-level perturbation will support
   strengthening low-level flow and the northward transport near 60 F
   surface dewpoints ahead of an eastward-advancing dryline in western
   OK/northwestern TX. 7-8 C/km mid-level lapse rates overspreading
   near 60 F dewpoints will boost SBCAPE into the 2000-3000 J/kg range
   by afternoon peak heating. Meanwhile, 30-40 kts of southwesterly 850
   mb flow overspread by 30-40 kt 500 mb westerlies will support mostly
   straight, elongated hodographs and 30-40 kts of effective bulk
   shear. Splitting supercells are expected to initiate off of the
   dryline. Given 20-30 F surface temperature/dewpoint spreads and
   modest low-level shear accompanying these supercells, the tornado
   risk should be limited, but large to very large hail is possible. 

   Some of the latest guidance also indicates the potential for
   supercells to merge and grow upscale into an MCS by evening,
   especially over central OK. Should this occur, severe gusts would
   become the main concern, at least with the leading round of storms.
   However, by evening, a veering but strengthening low-level jet atop
   earlier storm outflows may encourage back-building convection in
   central OK. Isolated severe hail/wind is possible with these storms.

   ...Southern Florida Peninsula...
   Latest high-resolution guidance consensus depicts scattered
   thunderstorms developing along the southeastern FL coast by Tuesday
   afternoon, and are poised to drift westward in tandem with a surface
   sea-breeze boundary. Forecast soundings depict 1000-1500 J/kg of
   tall/thin SBCAPE profiles. While vertical wind profiles should be
   weak overall, some of the forecast soundings depict modestly
   elongated upper-level hodographs, so some storm organization and
   associated potential for a damaging gust or two cannot be completely
   ruled out. However, confidence in this scenario is modest at best,
   precluding severe probabilities at this time.

   ..Squitieri.. 09/18/2023

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   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z