SPC AC 281734

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1234 PM CDT Thu May 28 2020

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NY SOUTH TO
   NORTHERN VA...AND SOUTHWEST TO EASTERN OH...

   ...SUMMARY...
   Severe thunderstorms are possible across an area centered over PA/NY
   Friday afternoon through Friday evening.

   ...Synopsis...
   Remnants of the central/eastern U.S. upper low will become fully
   absorbed into an eastward-moving northern-stream trough, as it
   traverses the Great Lakes and Northeast on Friday.  Meanwhile,
   though upper ridging will prevail over the West, an upper low moving
   northeastward over the eastern Pacific will impinge upon California
   through the second half of the period.

   At the surface, a cold front moving across the Upper Great
   Lakes/Midwest and into the Northeast, ahead of the advancing upper
   trough, will be the main feature of interest with respect to the
   convective forecast.  

   ...Portions of the Northeast/Central Appalachians area...
   Multiple bands/episodes of convection are expected across the upper
   OH valley and northeastern U.S. Friday, beginning early in the
   period as a zone of warm advection/QG forcing spreads across the
   area.  With a moist boundary layer in place, the onset of heating by
   late morning should support an increase in storms across the PA/NY
   vicinity.  With moderately strong mid-level southwesterly flow ahead
   of the advancing upper system spreading across the region, shear
   sufficient for organized convection suggests risk for locally
   damaging winds -- even with early-day convection.  

   Storms will likely continue/redevelop locally into the afternoon,
   with at least some degree of sustained severe risk, but a second
   peak in convective potential may occur later in the afternoon and
   into the evening.  This would occur as a result of convection
   developing across the mid and upper OH Valley -- ahead of the
   advancing cold front -- and spreading eastward with time, crossing
   the OH vicinity through the afternoon and reaching western portions
   of NY/PA by early evening.  Again -- with amply strong shear
   persisting, risk for locally damaging winds and hail would be
   possible.

   Farther south, storms are also expected to evolve in lee of the
   Appalachians, as afternoon destabilization occurs.  With flow aloft
   at least modestly supportive of some storm organization as far south
   as the Carolinas, a few stronger cells will likely become capable of
   producing gusty winds and marginal hail.  Storms should diminish
   across this region into the evening hours. 

   ...Southern MT/northern WY vicinity...
   Models suggest that a weak disturbance currently moving into
   northern CA will crest the upper ridge and turn eastward across ID
   toward southern MT/northern WY Friday.  With strong heating of the
   modestly moist boundary layer, model forecasts for around 500 J/kg
   mixed-layer CAPE development during the afternoon appear reasonable
   -- and likely sufficient for isolated storm development.

   With a belt of enhanced flow atop the area, around the northern
   periphery of the ridge, some potential for organization of
   convection is apparent, along with local risk for gusty/damaging
   winds with storms moving quickly eastward/east-southeastward through
   the afternoon and evening hours.

   ..Goss.. 05/28/2020

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