SPC AC 141952

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0252 PM CDT Sun Apr 14 2024

   Valid 142000Z - 151200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   OHIO EAST-NORTHEASTWARD ACROSS PENNSYLVANIA...

   ...SUMMARY...
   Severe thunderstorms are expected to develop late this afternoon in
   a narrow corridor across the upper Ohio Valley into Pennsylvania and
   vicinity. Damaging winds should be the main threat. Severe hail and
   perhaps a couple of tornadoes also appear possible as this activity
   spreads southeastward into this evening.

   ...Discussion...
   Aside from minor line tweaks in the northern Ohio area, the
   severe-weather risk areas remain unchanged, with prior forecast
   reasoning -- highlighting development of strong to severe storms
   this afternoon -- still valid.

   For additional short-term forecast information in this region,
   please refer to SWOMCD #435.

   Elsewhere, the portion of the thunder area across Nevada is being
   removed in this update.

   ..Goss.. 04/14/2024

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Apr 14 2024/

   ...Ohio Valley into the Mid-Atlantic and Northeast...
   Surface analysis late this morning shows the northeastern rim of 50s
   dewpoints over northern KY/southwest OH being quickly advected
   east-northeastward on a 40-kt west-southwesterly LLJ.  The Upper OH
   Valley is located immediately downstream of a mid-level vorticity
   maximum over Lake Michigan.  This disturbance will continue to move
   into the base of the larger-scale eastern Canada/Northeast U.S.
   mid-level trough.  An accompanying weak low will migrate eastward
   from the Great Lakes across NY, while a weak cold front extends to
   the west-southwest and is forecast to push east-southeast across the
   Lower Great Lakes before weakening and becoming draped across the
   Upper OH Valley late. 

   Continued low-level moist advection will likely result in upper 40s
   to low 50s surface dewpoints within a narrow corridor along
   and south of a cold front from OH into PA and southern NY.  Steep
   700-500 mb lapse rates due in part to cool mid levels (i.e., -18 deg
   C at 500 mb) and heating will yield 500-1250 J/kg MLCAPE by mid-late
   afternoon.  Surface-based thunderstorm initiation across this region
   will likely be delayed until 20-21Z or later, as lingering MLCIN and
   a cap gradually erodes. Initial development should be focused along
   the front across parts of eastern OH into western/central PA, with
   additional development eventually occurring into eastern PA and
   parts of southern NY.  Given strong deep-layer shear and favorable
   lapse rates, large hail may occur with the more robust cores
   initially. Some threat for a couple of tornadoes may also exist with
   quasi-discrete supercells early in the thunderstorm life cycle, as
   sufficient low-level shear will be present for updraft rotation. 
   But, with the surface front aligned mostly parallel to the enhanced
   westerly low/mid-level flow, upscale growth into small bowing
   clusters will likely occur as additional storms develop and cold
   pools merge as the band of storms moves southeastward.  Scattered
   damaging winds will then likely become the main threat with these
   clusters through the early evening.  As instability wanes after
   sunset, the wind threat will gradually decrease with
   southward/eastward extent.

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