SPC AC 141229

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0729 AM CDT Wed Aug 14 2019

   Valid 141300Z - 151200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FOR PARTS OF THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Widely scattered severe thunderstorms with very large hail and
   damaging winds are expected across the central High Plains this
   afternoon and evening. A few strong storms may be noted across the
   Gulf Coast to the southern Middle Atlantic.

   ...Central High Plains this afternoon through tonight...
   The larger-scale pattern is rather quiescent with a flat ridge over
   the Rockies and moderate west-northwest flow aloft over the central
   and northern High Plains.  Subtle speed maxima embedded in the flow
   will crest the ridge and move over the High Plains, the first and
   most apparent of which will progress from central WY to the central
   Plains this afternoon.  In the wake of a frontal passage and
   widespread convection last night across the central/southern High
   Plains, surface ridging extends from western SD to the TX
   Panhandle/NM border.  West of the ridge, boundary-layer dewpoints in
   the mid 50s have spread west to the Front Range in CO on upslope
   flow, and slightly lesser moisture extends northward across eastern
   WY.

   Steep midlevel lapse rates above a seasonally moist boundary layer
   with daytime heating will result in a corridor of MLCAPE of
   2000-3000 J/kg this afternoon from northeast CO across eastern WY. 
   Forcing for ascent will be rather weak near the higher terrain, so
   storm coverage within the corridor most favorable for supercells is
   somewhat in question.  Still, effective bulk shear of 40-50 kt with
   relatively straight hodographs will favor supercells capable of
   producing isolated very large hail.  The tornado threat will likely
   depend on a discrete storm interacting with the somewhat greater
   low-level shear/hodograph curvature expected from western NE into
   extreme northeast CO along the east edge of the greater buoyancy. 
   There will be some potential for storms to grow upscale into a small
   MCS tonight, with the more probable corridor for upscale growth
   centering near western NE and southwest SD where warm advection will
   be strongest on the nose of a 25-35 kt nocturnal low-level jet, as
   weak midlevel height falls occur tonight.

   ...Gulf Coast to the Mid-Atlantic this afternoon...
   The effective surface boundary, modulated by convective outflow,
   will continue to sag southward toward the Gulf Coast and
   southeastward toward the southeast Atlantic and Mid-Atlantic coasts.
   The richer moisture/buoyancy (PW greater than 2 inches and MLCAPE
   greater than 3000 J/kg) are expected along the southern fringe of
   the lingering clouds this morning, though vertical shear will be
   very weak and boundary/storm mergers will largely drive isolated
   downburst potential.  Somewhat stronger deep-layer shear is expected
   farther north toward Chesapeake Bay, which could compensate some for
   the weaker buoyancy and poor midlevel lapse rates.

   ...Northern IN and vicinity this afternoon...
   A diffuse surface front will provide a focus for thunderstorm
   development this afternoon, as a midlevel trough approaches from WI.
   Lingering low-level moisture and surface heating will support MLCAPE
   of 1000-1500 J/kg, while deep-layer vertical shear will be at least
   marginally favorable for organized/supercell storms.  Very weak
   low-level flow will greatly limit hodograph size/SRH magnitude, but
   there will be modest vertical vorticity along the surface boundary. 
   A couple of storms could be strong with hail/wind near severe
   criteria, and a brief/weak tornado cannot be ruled out.

   ..Thompson/Kerr.. 08/14/2019

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