SPC AC 251629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Thu Jun 25 2020

   Valid 251630Z - 261200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FOR PARTS OF THE NORTHERN PLAINS...

   ...SUMMARY...
   Scattered severe thunderstorms with hail and wind will be possible
   across the northern Great Plains, mainly between 2 to 11 PM CDT.
   Isolated severe thunderstorms are also possible south into the
   central/southern High Plains and west across Wyoming and northern
   Utah, and also across parts of the Mid-Atlantic and Southeast
   states.

   ...Northern Plains this afternoon/evening...
   A series of midlevel shortwave troughs will progress eastward from
   the northern Rockies/Great Basin to the northern/central Plains
   through early Friday.  Remnant MCVs are moving east-northeastward
   over the western SD/ND border and the NE Panhandle.  There appear to
   be two primary scenarios today for severe storm development - across
   the central/eastern Dakotas into NE with the remnant MCVs
   interacting with a surface front, and farther west into WY in
   advance of the shortwave trough moving eastward from southeastern
   ID.  Across the Plains, surface heating and a corridor of
   boundary-layer dewpoints in the 60s (beneath midlevel lapse rates
   greater than 8 C/km) will support thunderstorm development this
   afternoon.  There is some uncertainty regarding the influence of
   lingering clouds/convection with the MCVs, and deep-layer vertical
   shear will not be particularly strong, but MLCAPE in excess of 2000
   J/kg and the steep midlevel lapse will favor a threat for large hail
   and damaging winds with multicell clusters and marginal supercells.

   A separate area of storm initiation is expected across WY this
   afternoon, in the zone of ascent preceding the ID shortwave trough. 
   Moisture/buoyancy will be more limited with westward extent across
   WY this afternoon, but thermodynamic and wind profiles will support
   a threat for storm clusters capable of producing a few severe
   outflow gusts and isolated large hail.  Clusters of storms are also
   expected farther west into northern UT and NV, where gusty outflow
   winds will also be possible.  

   ...Portions of the Mid-Atlantic/Carolinas this afternoon...
   A midlevel trough over the OH Valley will move eastward to the
   Mid-Atlantic coast overnight.  This primary trough is preceded by a
   belt of somewhat enhanced midlevel flow across the Carolinas, with
   an embedded MCV near the eastern SC/NC border.  A cluster of
   thunderstorms is associated with the MCV, though this convection is
   already moving offshore.  In the wake of the MCV, a diffuse surface
   trough will move slowly eastward across the Carolinas/VA this
   afternoon.  Though midlevel lapse rates will be poor per regional
   12z soundings, surface heating will support MLCAPE of 1000-1500
   J/kg, with minimal convective inhibition.  Forcing for ascent will
   be rather weak, but widely scattered thunderstorms are probable east
   of the higher terrain.  Weak low-level flow/shear paired with
   stronger southwesterly flow aloft will result in hodographs with
   some counter-clockwise turning in the 1-3 km AGL layer.  The net
   result will be an environment that supports low-end splitting
   storms, capable of producing marginally severe hail and isolated
   strong wind gusts.

   ...Northeast Gulf coast and vicinity this afternoon...
   Surface heating south of the thicker cloud band will boost buoyancy
   where boundary-layer dewpoints are in the mid 70s.  Widely scattered
   thunderstorms are expected later this afternoon along the
   differential heating zone, where a lingering belt of 30-40 kt
   westerly flow in the 700-500 mb layer will support primarily
   multicell clusters with an attendant threat for at least isolated
   damaging gusts this afternoon.

   ...Central FL peninsula this afternoon...
   Strong surface heating is underway across central FL, and a few
   thunderstorms are expected later this afternoon along a diffuse
   convergence zone across central FL, as well as immediately inland
   along sea breeze circulations.  Wind profiles are weak, but
   thermodynamic profiles will support the potential for wet
   microbursts and isolated damaging winds.

   ...Western/central PA/NY this afternoon...
   A few low-topped thunderstorms will be possible this afternoon as a
   midlevel trough moves over this area from the upper OH Valley, and
   steep low-level lapse rates could support isolated strong outflow
   gusts.  However, limited buoyancy suggests that any severe-storm
   threat is too small to warrant an outlook area.

   ..Thompson/Wendt.. 06/25/2020

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