SPC AC 270558

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Sat Jun 27 2020

   Valid 281200Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   VIRGINIA AND THE CAROLINAS...AND VICINITY...

   ...SUMMARY...
   A few severe storms are expected across portions of the Northeast
   and Ohio Valley, and southward into the Carolinas and vicinity on
   Sunday.  Isolated stronger storms and local severe potential is also
   expected from the Wyoming vicinity into the northern High Plains,
   and eastward to the Upper Mississippi Valley.

   ...Synopsis...
   An upper low over Quebec is forecast to shift slowly southward with
   time, while several disturbances rotate through the broader area of
   cyclonic flow aloft over the eastern quarter of the country.  In the
   West, an upper low initially centered over the Pacific Northwest
   will dig slowly southeastward with time, with surrounding cyclonic
   flow to cover the western third of the country by the end of the
   period.

   At the surface, a cold front will advance southward across the
   Intermountain West, while lingering nearly in place across the
   northern High Plains.  in the East, a weak front will move
   southeastward across New England and the Northeast through the
   period.

   ...The Northeast to the Carolinas vicinity...
   As upper troughing lingers across the Northeast Sunday, scattered
   afternoon showers and thunderstorms are forecast to develop across a
   large area, as at least weak diurnal destabilization occurs. 
   Moderate northwesterly flow aloft should promote some storm
   organization along with fast cell motions, yielding local risk for
   gusty/damaging winds.  

   Greatest risk appears likely to exist across parts of Virginia and
   the Carolinas vicinity.  Here, models hint that a short-wave feature
   aloft -- embedded within the broader northwesterly cyclonic flow --
   will move across the region during the afternoon.  With a more
   unstable airmass expected to evolve as compared to areas farther
   north, storms will likely develop over the higher terrain and then
   move quickly east-southeastward -- possibly growing upscale into
   bands, locally.  With moderate flow (30 to 40 kt) through a deep
   layer, potential for somewhat more widespread wind damage across
   this portion of the risk area warrants upgrade to 15% wind/SLGT risk
   -- focused during the afternoon and early evening hours.

   ...Wyoming vicinity into the northern High Plains/Dakotas...
   As the western upper low/trough digs southward, a surface cold front
   is forecast to linger in a north-northeast to south-southwest manner
   across the northern High Plains, while progressing southward on its
   western flank across the Great Basin.  Isolated storms are expected
   to develop near the boundary during the afternoon, though modest
   instability expected across much of the area should limit storm
   intensity despite ample shear.  Greater CAPE into the western
   Dakotas is expected, but capping should hinder overall convective
   coverage to a large degree.  As such, 5%/MRGL risk for hail/wind
   potential still appears an appropriate forecast at this time.

   ...Mid Missouri and Upper Mississippi Valleys...
   Much uncertainty persists across the north-central portions of the
   country, with a short-wave mid-level disturbance progged to evolve
   across the Mid Missouri Valley vicinity and move northward with
   time.  With a rather weak surface warm front expected to be lifting
   northward across the north-central U.S. with time, afternoon storm
   development is expected -- though models differ quite a bit with
   regards to the evolution of the upper disturbance, and as a result
   the surface warm front and possible/associated frontal wave.  Thus,
   while risk for locally damaging winds and hail -- and even tornado
   potential -- could ultimately evolve, will introduce only 5%
   probability at this time due to ongoing/considerable uncertainty.

   ..Goss.. 06/27/2020

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