SPC AC 231647

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1147 AM CDT Sat Jun 23 2018

   Valid 231630Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   PLAINS TO THE TN VALLEY...ACROSS THE MID ATLANTIC...AND THE CENTRAL
   HIGH PLAINS...

   ...SUMMARY...
   Scattered severe thunderstorms are expected especially this
   afternoon and evening from the southern Plains to the lower
   Mississippi Valley and a portion of the Southeast States. Other
   severe storms are expected over the Middle Atlantic region and
   central High Plains.

   ...TN and lower MS Valley region today...
   The remnants of an overnight MCS, now moving into northwest AL and
   southern middle TN, will be accompanied by some threat for damaging
   winds about as far east as southeast TN and northwest GA through
   early afternoon, given a belt of 40+ kt flow near 700 mb (enhanced
   some by the MCV with the convection).  However, the widespread
   clouds/convection ongoing farther to the south in AL casts doubt of
   the degree of destabilization possible in advance of these storms. 
   Otherwise, additional strong/isolated severe storms could evolve
   from the ongoing central AL storms into GA, or develop this
   afternoon along the residual outflow from southeast AR into MS and
   eventually spread into central AL (along the southern fringe of the
   current storms).  Damaging outflow gusts will be the main threat.

   ...Northwest TX into southern OK this afternoon into early
   tonight...
   The outflow boundary from overnight and ongoing convection has
   consolidated immediately north of I-20 across north central and
   northeast TX, and the boundary may begin to retreat a little to the
   north across northwest TX this afternoon.  An influx of low-mid 70s
   boundary-layer dewpoints into the boundary, along with daytime
   heating and midlevel lapse rates near 9 C/km, will boost MLCAPE into
   the 3000-4000 J/kg range this afternoon.  This corridor will lie
   along the southern fringe of the stronger midlevel flow (near or
   above 30 kt), with some enhancement to low-level shear along the
   boundary.  The net result will be profiles sufficient for supercells
   where deep mixing reduces convective inhibition across northwest TX,
   and in the warm advection zone to the north into southern OK this
   afternoon/evening.  The strongest storms could produce isolated very
   large hail and damaging gusts.

   ...Chesapeake region this afternoon/evening...
   A midlevel trough over the upper OH Valley will progress
   east-northeastward to southern New England tonight.  Embedded speed
   maxima will continue to rotate around the southeast periphery of the
   trough and interact with a diffuse lee trough across VA.  The richer
   low-level moisture/buoyancy should remain near Chesapeake Bay
   through the afternoon, while mid-upper flow/shear will be sufficient
   for organized storms.  A few supercells will be possible, with a
   primary threat for a few damaging gusts.

   ...Central High Plains this afternoon through early tonight...
   Another midlevel trough is beginning to amplify and will move from
   the northern Rockies to WY/CO tonight.  Low-level moisture is
   returning northward across southeast CO in the wake of overnight
   convection, and profiles will become sufficient for supercells by
   this afternoon.  A few storms should form along the Palmer Divide,
   and potentially the Raton Mesa, and then spread east-southeastward
   over the Plains this evening.  There are still some concerns
   regarding storm coverage, but any supercells that form will be
   capable of producing large hail and damaging winds, and storms could
   grow into a small cluster and persist into early tonight.

   ..Thompson/Smith.. 06/23/2018

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