SPC AC 230605

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0105 AM CDT Sat Jun 23 2018

   Valid 231200Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   PLAINS THROUGH THE SOUTHEAST STATES AND OVER THE MIDDLE ATLANTIC
   REGION...

   ...SUMMARY...
   Scattered severe storms are expected from the southern Plains to
   lower Mississippi Valley and a portion of the Southeast States.
   Other severe storms are expected over the Middle Atlantic region.
   More isolated strong to severe storms might occur over a portion of
   the central and northern Plains.

   ...Southern Plains...

   Outflow boundary from ongoing MCS will reinforce stationary front
   currently situated near the OK/TX border. This boundary might shift
   a little farther north into OK today. Diabatic heating of the moist
   warm sector will contribute to strong instability in the vicinity of
   and south of the front (2000-3000 J/kg MLCAPE), but a capping
   inversion should limit thunderstorm initiation much of today.
   Current thinking is that storms may initiate by late afternoon near
   the intersection of the dryline and front across northwest TX.
   Additional storms may also develop farther east within frontal zone,
   especially during the evening as the southerly low-level jet
   strengthens.  A belt of modest winds aloft with 25-30 kt at 500 mb
   will result in 35-40 kt effective bulk shear near/north of the front
   where surface winds will remain backed to easterly. Weaker shear
   will reside in warm sector. Both multicell and some supercell
   structures will be possible with damaging wind and large hail the
   main threat from late afternoon into the evening. Higher severe
   probabilities may be needed in later updates, but uncertainty
   imposed by ongoing MCS regarding where the corridor of greater
   severe potential will be located precludes an upgrade at this time.

   ...Lower Mississippi Valley through Southeast States....

   MCS may still be in progress over the lower MS Valley region and
   most likely over AR. It remains uncertain whether this activity will
   be severe, but remnant MCV and outflow boundaries accompanying the
   MCS will provide a focus for additional development during the day.
   The downstream atmosphere will likely become moderately unstable
   with up to 2500 J/kg MLCAPE. A belt of stronger winds aloft will
   accompany the MCV/shortwave trough, and storms will likely
   reintensify during the afternoon. The environment appears supportive
   of swaths of damaging wind through the afternoon into the early
   evening.

   ...Middle Atlantic region...

   Warm front will lift north through VA and into PA during the day
   ahead of a cold front accompanying a shortwave trough. Diabatic
   warming of the moist warm sector will result in moderate
   instability. A belt of stronger winds aloft will accompany the upper
   low as it shifts northeast and transitions to an open wave. Storms
   are expected to develop over the higher terrain with a lee trough
   across central VA also becoming a focus for development. Storms may
   organize into broken bands as they develop east with also some
   potential for mid-level updraft rotation given effective bulk shear
   increasing to 30-40 kt. Damaging wind will be the main threat, but
   some hail will also be possible.

   ...Central through northern Plains...

   Ascent accompanying a shortwave trough moving southeast through the
   northern Rockies and diabatic heating will promote thunderstorm
   development over the higher terrain. High based storms capable of
   downburst winds and hail appears to be the main threat.

   Farther east across SD into eastern NE, surface trough accompanying
   a lead shortwave trough will provide a focus for storm development
   during the afternoon.  Modest winds aloft will promote multicell
   storm modes with a few instances of marginally severe hail and gusty
   winds possible.

   ..Dial/Wendt.. 06/23/2018

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