SPC AC 011617

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1117 AM CDT Wed Sep 01 2021

   Valid 011630Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   MID-ATLANTIC STATES...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NE PANHANDLE TO
   WESTERN/CENTRAL SD...

   ...SUMMARY...
   Several tornadoes and scattered damaging winds appear probable
   across parts of the Mid-Atlantic States as the remnants of Ida move
   through the region into this evening. The greatest tornado threat is
   expected from central Maryland to southern New Jersey.

   ...Mid-Atlantic States...
   The remnants of TC Ida will move east-northeast from southeast WV
   across northern VA through the afternoon to the southern New England
   coast overnight. Mid 70s boundary-layer dewpoints are prevalent
   across eastern VA to southern NJ to the south of a northward
   drifting warm front. Here to, surface temperatures have warmed into
   the 80s amid scattered to broken cloudiness which is already
   supporting a plume of MLCAPE from 500-1500 J/kg. Low to mid-level
   vertical shear will increase into this evening as the remnants of
   Ida become further absorbed into the deepening longwave trough
   emanating south from QC.

   An initial arc of low-topped showers has developed across parts of
   north to southeast VA, largely ahead of schedule compared to much of
   the CAM guidance. As large-scale ascent and instability continue to
   further increase, it seems probable that this arc will eventually
   deepen into a broken band/cluster with several embedded supercells
   that will spread east-northeast towards the Atlantic coast into this
   evening. The relatively greatest tornado threat should exist along
   the baroclinic zone from central MD into south NJ with several
   tornadoes and occasional damaging gusts probable. See MCD 1668 for
   further near-term discussion. 

   Low-level static stability and the exact cyclone track will
   determine the extent of the tornado threat this evening into tonight
   across Long Island and the immediate southern New England coast.
   Otherwise, damaging winds will be possible given the rather strong
   low to mid-level wind fields. 

   Vertical shear will also be progressively weaker farther to the
   south of the warm front. Still, it should be adequate given the
   buoyancy for some threat of an isolated tornado or two into eastern
   NC, as well as the potential for a few damaging gusts with scattered
   storms along and just ahead of the primary wind shift trailing
   southward from the Ida remnant cyclone.

   ...NE Panhandle into western/central SD...
   Lee cyclogenesis is expected this afternoon across northeast CO, on
   the southern fringe of southwest mid-level flow. An inverted
   trough will extend north of the lee cyclone, across the NE Panhandle
   into western SD, and a slow-moving northwest/southeast-oriented warm
   front will intersect the trough across the NE Panhandle.  With
   daytime heating/mixing, convergence and low-level ascent should be
   sufficient to weaken convective inhibition and allow at least
   isolated thunderstorm development late this afternoon across the NE
   Panhandle. The storm environment will favor cluster with a couple
   embedded supercells moving north-northeast along the trough, with an
   attendant threat for large hail and severe gusts into early tonight.

   ..Grams/Lyons.. 09/01/2021

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