SPC AC 300547

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1247 AM CDT Sun Jun 30 2024

   Valid 301200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FROM EASTERN AND SOUTHERN NEW ENGLAND INTO THE
   MID-ATLANTIC...AND THIS EVENING INTO EARLY TONIGHT ACROSS MT...

   ...SUMMARY...
   Scattered damaging winds will be possible across parts of the
   Northeast and Mid-Atlantic States this afternoon/evening. Hail and
   damaging winds may also occur from eastern Montana into western
   North Dakota.

   ...New England into the Mid-Atlantic this afternoon/evening...
   A midlevel shortwave trough over Lower MI will progress eastward
   toward NY/PA by early tonight, while an associated surface cold
   front moves eastward across New England and southeastward across the
   central Appalachians.  A corridor of boundary-layer dewpoints in the
   low 70s and surface heating in cloud breaks will support diurnal
   destabilization ahead of the cold front/pre-frontal trough which
   will focus thunderstorm development by early-mid afternoon.  Though
   midlevel lapse rates will not be particularly steep, MLCAPE is
   expected to increase to 1500-2000 J/kg as midlevel flow also
   increases with largely straight, but sufficiently long hodographs. 
   The net result will be a favorable environment favorable for
   organized storm clusters/line segments, as well as a few supercells,
   capable of producing damaging winds, isolated large hail and perhaps
   a tornado into the evening across southern and eastern New England.

   Deep-layer vertical shear will weaken with southwestward extent into
   VA/NC, where the storm mode is expected be predominately multicell
   clusters.  Still, thermodynamic profiles will support the potential
   for occasional wind damage with downbursts.

   ...Northern/central High Plains this evening into tonight...
   A midlevel shortwave trough over WA/OR will move eastward over the
   northern Rockies by tonight, with downstream lee cyclogenesis
   expected across WY/MT.  Though the richer low-level moisture will be
   confined to KS southward along a baroclinic zone, there will be a
   modest increase in low-level moisture across the central/northern
   High Plains on southeasterly low-level flow.  The somewhat larger
   buoyancy and weaker convective inhibition are expected closer to the
   high terrain, with the more likely area for storm-cluster
   development over the mountains of southern MT in the zone of ascent
   preceding the midlevel trough.  The storms will subsequently spread
   east-northeastward toward eastern MT with an accompanying threat for
   severe outflow winds of 60-70 mph.  Large hail (mainly 1-1.75 inches
   in diameter) will also be possible with any embedded supercell
   structures.

   Farther south, isolated thunderstorm development will be possible
   immediately east of the higher terrain from WY into CO.  Forecast
   wind profiles will be at least marginally favorable for supercells,
   though storm coverage is in question.  The southern fringe of the
   stronger midlevel flow and the northwest edge of the monsoonal
   moisture plume may support an isolated wind-damage threat into
   western CO. 

   ...Southern AZ this afternoon/evening...
   Around the southwestern periphery of a midlevel high over the
   southern Plains, low-midlevel moisture has been gradually increasing
   from southern NM into AZ.  In the wake of scattered overnight
   storms, cloud breaks will allow surface heating/destabilization
   across southeast/south central AZ into the afternoon, which will
   drive moderate buoyancy (MLCAPE up to 1000 J/kg).  Convection will
   form over the high terrain of southeast AZ and spread westward
   through late afternoon/evening in response to east-southeasterly
   midlevel flow of 20-25 kt.  A typical/deep mixed boundary layer
   coupled with the moderate buoyancy will support a few strong outflow
   gusts (50-60 mph) with precipitation-loaded downdrafts.

   ..Thompson/Squitieri.. 06/30/2024

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