SPC AC 011730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Sat Aug 01 2020

   Valid 021200Z - 031200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHEAST...

   ...SUMMARY...
   Severe thunderstorms capable of producing damaging winds, a couple
   tornadoes, and perhaps some hail will be possible over portions of
   the Northeast on Sunday.

   ...Northeast into the Mid-Atlantic...
   A large-scale upper trough will persist over much of the
   central/eastern CONUS on Sunday. An embedded shortwave trough is
   forecast to move across the Northeast and Mid-Atlantic through the
   period. A related surface low initially near Lake Erie should
   likewise develop northeastward along the international border and
   into southern Quebec by early Sunday evening. A warm front should
   lift northward across much of the Northeast through the day, with a
   trailing cold front expected to sweep eastward across much of the
   Northeast and Mid-Atlantic through the period.

   Low-level warm advection across the Northeast should aid a gradual
   increase in low-level moisture through the day. Even though
   mid-level lapse rates should remain modest, diurnal heating across
   the warm sector will likely aid at least 1000-1500 J/kg of MLCAPE by
   Sunday afternoon. Stronger instability (MLCAPE 2000-2500+ J/kg)
   appears possible farther south across parts of eastern PA into NJ
   and the southern NY vicinity, where greater heating should occur.
   Both low and mid-level flow is expected to be rather strong for
   early August, and forecast effective bulk shear of 30-40 kt may
   support both bowing line segments and perhaps a few supercells. 

   Primary threat should be damaging wind gusts with storms that
   develop Sunday afternoon given steepening low-level lapse rates and
   increasing low/mid-level flow through the day. A couple tornadoes
   also appear possible with the enhanced low-level flow if a more
   discrete storm mode can be maintained. The Slight Risk has been
   expanded northward/eastward to account for greater potential storm
   coverage. These strong to severe storms should gradually weaken with
   eastward extent into New England Sunday evening as instability
   wanes. Farther south into the Mid-Atlantic, additional storms may
   form along/east of the Appalachians. Although deep-layer shear will
   be somewhat weaker farther south, steepened low-level lapse rates
   may still encourage isolated damaging wind gusts.

   ...Southern/Central Rockies into the adjacent High Plains...
   Generally north-northwesterly mid-level flow on the east side of an
   upper ridge will persist across the southern/central Rockies and
   adjacent High Plains on Sunday. Although low-level easterly flow
   across these regions should remain fairly weak, strengthening flow
   at mid/upper levels may still support up to 25-40 kt of effective
   bulk shear. Low-level moisture may remain somewhat limited,
   especially across the higher terrain, but it should still be
   sufficient in tandem with diurnal heating to support around 500-1500
   J/kg of MLCAPE. A supercell or two may ultimately evolve
   southeastward across the central High Plains late Sunday
   afternoon/early evening. Southeastward-moving storm clusters also
   appear possible, especially from southeastern CO into NM and the
   TX/OK Panhandles. Both isolated large hail and severe wind gusts may
   occur with this activity, with the wind threat probably becoming
   more dominant across the southern High Plains. With the lack of
   stronger forecast large-scale ascent, confidence remains too low in
   a more focused corridor of severe potential to include higher
   hail/wind probabilities at this time.

   ...Florida Atlantic Coast...
   The latest forecast track from the National Hurricane Center
   regarding Isaias continues to suggest that the hurricane will
   approach very near the east-central FL Coast on Sunday. Current
   expectations are for the more favorable tornado environment to
   generally remain offshore through the period. However, if Isaias
   makes even a small westward shift in its track, then low
   probabilities for a tornado or two would need to be considered along
   the immediate FL Atlantic Coast.

   ..Gleason.. 08/01/2020

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