SPC AC 251646

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1146 AM CDT Tue May 25 2021

   Valid 251630Z - 261200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN PLAINS AND UPPER MIDWEST...

   ...SUMMARY...
   Scattered severe thunderstorms with large hail and damaging winds as
   the primary hazards are possible across parts of the Upper Great
   Lakes and the southern Great Plains, mainly from mid-afternoon
   through evening.

   ...Central/Southern Plains...
   Late afternoon to evening thunderstorm development is still
   anticipated with isolated to widely scattered coverage along the
   dryline from the Texas Trans-Pecos north towards the composite
   front/outflow intersection in the Texas South Plains/Panhandles into
   south-central Kansas. Although mid-level westerlies will remain weak
   under the influence of modestly building upper heights, moderate to
   strong destabilization is expected this afternoon with ample MLCAPE
   generally on the order of 2000-3000 J/kg. 

   While deep-layer shear will be modest, a few organized multicell
   clusters with embedded supercell structures should prove favorable
   for isolated to potentially scattered large hail and severe wind
   through this evening, with the likely evolution of multiple
   southeastward-moving clusters this evening. Given the degree of
   buoyancy and steepness of lapse rates across the Permian Basin to
   Concho Valley, and the influence of the modifying outflow across the
   West Texas South Plains towards the Edwards Plateau, significant
   severe appears most possible in these regions.

   ...Upper Great Lakes...
   A shortwave trough over southern Manitoba/northern North Dakota will
   modestly amplify as it continues east-southeastward along the
   International Border toward the Lake Superior vicinity by tonight.
   Primary surface cyclogenesis will occur over northern Ontario, while
   a cold front progresses eastward and reaches a northwest
   Wisconsin/southeast Minnesota to northwest Iowa corridor by around
   peak heating. Although plentiful cloud cover persists across the
   warm sector at late morning, gradual clearing will occur with ample
   heating and 60s F surface dewpoints likely yielding 1000-2000 J/kg
   MLCAPE by mid/late afternoon.

   It appears adequate low-level convergence will be present for
   isolated/widely scattered thunderstorm development initiating across
   the Minnesota Arrowhead and western Wisconsin and possibly southeast
   Minnesota by around 20-22Z. Relatively long hodographs (40-55 kt
   effective shear) related to nearly unidirectional southwesterly
   winds will support some initial supercells capable of severe hail
   and possibly some tornado risk. Strengthening flow in the mid-levels
   should otherwise support the possibility of upscale growth into
   organized clusters with embedded mid-level updraft rotation. Overall
   convective intensity should wane into late evening/overnight as
   storms approach the Lake Michigan vicinity.

   ...Northeast Texas/ArkLaTex...
   Related to persistent/generally weakening convection, multiple weak
   MCVs appear to exist across north-central Texas and eastern
   Oklahoma. Preceding these MCVs and a linear cluster of storms across
   north Texas (near the DFW Metroplex at late morning), the air mass
   is moist (upper 60s to lower 70s F surface dewpoints) and will
   likely become moderately unstable this afternoon. A renewed
   intensification of storms seems probable this afternoon as the
   boundary layer destabilizes. Some of these stronger storms will be
   capable of isolated wind damage, while the moist environment and
   residually strong MCV-related low-level winds could support a brief
   tornado risk.

   ...West New York/Northwest Pennsylvania...
   Strong heating is expected across western portions of New
   York/Pennsylvania which will allow surface temperatures to warm
   towards the low 80s in the lee of Lake Erie. Although deep-layer
   flow will not be that strong, steep low-level lapse rates and MLCAPE
   around 500 J/kg could support a couple robust cells capable of
   producing locally damaging winds.

   ...Southeast Oregon/southern Idaho...
   Forcing for ascent related to an eastward-moving shortwave trough
   coupled with a semi-moist environment and differential heating will
   contribute to increasing thunderstorm potential this afternoon, some
   of which may be strong to locally severe. Sufficient
   moisture/buoyancy may exist for hail, particularly across southeast
   Oregon into southwest Idaho, while a well-mixed boundary layer and
   strengthening mid-level southwesterly winds may contribute to some
   strong thunderstorm wind gusts.

   ..Guyer/Leitman.. 05/25/2021

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