SPC AC 231953

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0253 PM CDT Sun Aug 23 2020

   Valid 232000Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH
   DAKOTA...

   ...SUMMARY...
   Isolated large hail and damaging winds will be possible this
   afternoon into tonight across parts of the northern Plains. Isolated
   damaging winds are possible today across parts of the Northeast and
   Mid-Atlantic States. An isolated tornado may occur early Monday
   morning near the southeast Louisiana coast.

   ...Discussion...
   No appreciable change was made to the previous convective outlook.

   ..Smith.. 08/23/2020

   .PREV DISCUSSION... /ISSUED 1139 AM CDT Sun Aug 23 2020/

   ...Northern Plains this afternoon and tonight...
   A surface cold front will settle southward across North Dakota
   today. Given minimal larger-scale forcing for ascent and only
   shallow lift along the surface front, the prospects for
   surface-based convection should be limited to a zone of deep mixing
   across western South Dakota along a surface trough, where gusty
   outflow winds and perhaps some hail are possible. 

   A more probable/certain expectation is for elevated storms to
   develop and increase this evening across south-central/southeast
   North Dakota as warm/moist advection focuses along and north of the
   surface front. Some organized/supercell structures may occur within
   the band of elevated storms, which would locally enhance the threat
   for large hail. Isolated strong to locally damaging gusts could also
   occur despite the elevated nature of the updrafts, given some
   potential for residual dry air to linger just above the surface,
   with DCAPE approaching 1000 J/kg.

   ...New York/New England this afternoon...
   A low-amplitude shortwave trough over Lake Huron this morning will
   move over New England tonight. Prior to that, forcing for ascent
   will be weak/nebulous from New York into New England, within a warm
   sector characterized by boundary-layer dewpoints mainly in the
   low-mid 60s F with afternoon surface temperatures of 85-90 F. 
   Still, daytime heating/mixing and terrain influences should be
   sufficient to initiate at least widely scattered storms this
   afternoon from southern/eastern New York eastward across MA/VT/NH
   and southern Maine. While deep-layer shear will not be strong, steep
   low-level lapse rates, SBCAPE of 1000-1500 J/kg, and DCAPE
   approaching 1000 J/kg will favor multicell/pulse storms capable of
   producing isolated damaging downburst winds for a few hours this
   afternoon before ending this evening.  

   ...Mid-Atlantic States/Delmarva...
   Showers/few thunderstorms are occurring across the region this
   morning into midday, with additional isolated thunderstorms expected
   to develop and increase to the west/southwest of this early evening
   activity. Ample insolation, a moist air mass (low to mid 70s F
   surface dewpoints), and adjustments to observed morning soundings
   imply as much as 2000-2250 J/kg MLCAPE may materialize this
   afternoon. There appears to be at least some potential for
   microbursts with localized wind damage being a possibility.

   ...Southeast Louisiana coast late tonight/early Monday...
   Marco is forecast by NHC to become a hurricane and is expected to
   move north-northwestward and make landfall along the southeast
   Louisiana coast on Monday. Reference the National Hurricane Center
   forecasts for the latest details. The expected position/timing of
   Marco and its relatively small size suggests any zone favorable for
   supercells will not approach the coast until early Monday morning.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z