SPC AC 040541

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1241 AM CDT Thu Jun 04 2020

   Valid 041200Z - 051200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE NORTHERN
   HIGH PLAINS THROUGH MID MISSOURI VALLEY...THE SOUTHERN PLAINS AS
   WELL AS THE MIDDLE ATLANTIC REGION...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the northern and
   Central Plains/Mid Missouri Valley/upper Midwest today, with other
   strong/severe thunderstorms expected over the southern High Plains
   as well as the Mid-Atlantic region.

   ...Northern Plains through Mid Missouri Valley region...

   A cold front will advance east through the upper MS Valley with the
   southwestern extension of this boundary likely to stall across SD.
   Weak impulses embedded within the belt of stronger westerlies will
   traverse the northern Plains. Corridor of modest low-level moisture
   with 50s to mid 60s F dewpoints will reside in vicinity of stalled
   front beneath 7.5-8.5 C/km mid-level lapse rates, resulting in
   1500-2000 J/kg MLCAPE. Widely scattered storms are expected to
   develop during the afternoon and evening in vicinity of the stalled
   front with additional storms possibly spreading east off of the
   higher terrain. This region will reside within belt of stronger
   westerlies resulting in 40-50 kt effective bulk shear supportive of
   supercells, but some storms may congeal into clusters as they
   develop east southeast with large to very large hail and damaging
   wind the main threats. There remains some uncertainty regarding
   where the best storm coverage will be, but an upgrade to enhanced
   risk may be warranted over a portion of this region once this can be
   ascertained.  

   ...Southern Plains...

   The atmosphere should become moderately to strongly unstable east of
   a lee trough/dryline that is forecast to become established across
   the southern High Plains during the day. Near-surface dewpoints from
   the upper 50s to mid 60s F beneath steep lapse rate plume will
   contribute to MLCAPE from 2000-3000 J/kg as strong diabatic heating
   occurs during the afternoon. Storms are expected to develop along
   this boundary from southwest KS to the TX Panhandle as the surface
   layer destabilizes and as a weak shortwave trough moving along
   periphery of upper ridge is favorably timed with peak heating.
   Storms will be high based with modest (25-35 kt) vertical shear
   supportive of mostly multicells, but some marginal supercell
   structures are also possible. Activity may eventually congeal into
   an MCS during the evening. Large hail and damaging wind will be the
   primary threats. 

   ...Mid Atlantic region...

   A corridor of low to mid 60s F dewpoints will persist east of the
   higher terrain and along southern periphery of belt of modest
   westerlies. By early to mid afternoon, MLCAPE from 1500 to 2000 J/kg
   is expected from VA and MD into southern PA and NJ. Storms are
   expected to develop over the higher terrain and along lee trough as
   the boundary layer destabilizes. Vertical shear will remain weak,
   but 25-35 kt deep layer flow will support storms spreading east off
   the higher terrain, possibly evolving into loosely organized
   clusters capable of strong to damaging wind gusts.

   ..Dial/Lyons.. 06/04/2020

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