SPC AC 241718

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1218 PM CDT Sat Sep 24 2022

   Valid 251200Z - 261200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY ACROSS
   PARTS OF THE UPPER OHIO VALLEY INTO THE NORTHERN MID ATLANTIC
   REGION...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the upper Ohio Valley into
   the northern Mid Atlantic coast vicinity Sunday, posing at least
   some risk for severe weather.

   ...Synopsis...
   Mid/upper flow is in the process of amplifying across the
   mid-latitude Pacific into North America.  This includes prominent
   ridging building across the Pacific coast through the Rockies and,
   by late Sunday into Sunday night, a significant short wave trough
   digging downstream, across the Upper Midwest into Ohio Valley.  A
   preceding short wave trough is forecast to accelerate east of the
   lower Ohio Valley, before turning northeastward across the northern
   Mid Atlantic states and New England, within larger-scale troughing
   evolving across the Mississippi Valley through the Atlantic
   Seaboard.

   Models suggest that this evolving regime will be accompanied by the
   development of a broad surface low across parts of the lower Great
   Lakes into St. Lawrence Valley vicinity, and a reinforcing intrusion
   of cooler and/or drier air across much of the nation east of the
   Rockies Sunday through Sunday night.  However, this is occurring in
   the wake of a substantive prior intrusion of cool/dry air, and in
   the wake of the Fiona, which is forecast to migrate north of the
   Canadian Maritimes into the Labrador Sea.  As a result, it appears
   that low-level forcing for ascent and moisture return within the
   warm sector of the developing low will remain limited, which may
   tend to suppress the potential for vigorous thunderstorm development
   during this period.

   ...Mid/upper Ohio Valley into northern Mid Atlantic...
   The mid-level cold pool, and forcing for ascent in the exit region
   of the strong mid-level jet streak accompanying the lead short wave
   perturbation, seem likely to become the primary focus for any strong
   thunderstorm development Sunday.  As the wave shifts east of the
   mid/upper Ohio Valley by midday, toward the  northern Mid Atlantic
   coast through early evening, it appears that boundary-layer
   destabilization will remain rather modest.  CAPE is generally
   forecast to peak around or below 500 J/kg along a developing warm
   frontal zone across parts of central and eastern Pennsylvania into
   Long Island/southern New England, and below 1000 J/kg ahead of the
   developing cold front across the Allegheny Plateau vicinity. 
   However, this could be sufficient to support scattered thunderstorm
   development and, in the presence of strong shear (beneath 30-70+ kt
   flow in the 850-500 mb layer), at least some potential for organized
   severe thunderstorm development.  This may include isolated to
   widely scattered supercells, particularly along the warm frontal
   zone, where various model output suggests that low-level hodographs
   might become supportive of the risk for a tornado or two, before
   convection wanes by Sunday evening.

   ..Kerr.. 09/24/2022

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