SPC AC 050532

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1232 AM CDT Wed Aug 05 2020

   Valid 061200Z - 071200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM MONTANA
   SOUTHWARD INTO THE SOUTHERN PLAINS...AND ACROSS PARTS OF THE
   MID-ATLANTIC REGION...

   ...SUMMARY...
   Isolated severe storms are possible Thursday afternoon and evening
   from Montana southward through the central High Plains and into
   portions of the southern Great Plains. Gusty winds and hail will be
   possible with the strongest storms. Additional strong storms could
   produce locally damaging winds across parts of the Mid-Atlantic
   vicinity.

   ...Montana...

   An amplified upper ridge will be oriented over the High Plains
   Thursday morning, shifting slowly eastward over the Great Plains by
   Friday morning. Meanwhile, a shortwave trough will shift eastward
   across the Pacific Northwest and northern Rockies during the
   forecast period. South/southerly low level flow will transport
   modest boundary-layer moisture westward across MT toward the
   Continental Divide, with mainly mid 40s to mid 50s F dewpoints
   forecast. This will tend to limit instability across MT, but
   diurnally-driven isolated to scattered thunderstorms are expected
   over higher terrain by mid/late afternoon. As the shortwave trough
   ejects across the northern Rockies after 00z, deep layer
   southwesterly flow will increase. This should result in some
   increase in storm intensity during the evening into early overnight
   hours as convection shifts off higher terrain toward central MT.
   Clusters of storms capable of locally damaging gusts and isolated
   hail could persist across central MT into the overnight hours,
   though boundary layer inhibition will increase with loss of daytime
   heating, and overall severe threat could be limited by the ill-timed
   ejection of the shortwave trough during the overnight hours. 

   ...Central/Southern High Plains vicinity...

   Further south, convection may be ongoing Thursday morning across
   parts of southern KS or northern OK. Marginal probabilities have
   been included as some gusty wind potential could be ongoing with
   this activity before decaying through the morning hours. Instability
   will be a bit stronger across the High Plains as dewpoints will
   generally be higher, from the mid 50s to mid 60s F. Steep midlevel
   lapse rates will aid in weak to moderate destabilization by peak
   heating and thunderstorms are expected to develop along higher
   terrain by mid/late afternoon. Overall, effective shear will remain
   modest, but adequate for a few semi-organized cells/clusters. Steep
   low level lapse rates with inverted-v sub-cloud thermodynamic
   profiles indicated potential for enhancement of outflow winds and
   gusty winds will be the main concern with this activity, though
   isolated hail is also possible. Guidance suggests some upward
   developing cluster could track eastward across the OK/TX Panhandle
   vicinity during the evening/overnight, potentially along residual
   outflow from morning convection. If this occurs, some potential
   could exist for a marginal severe threat persisting eastward into
   parts of western OK/KS during the nighttime hours. 

   ...Mid-Atlantic vicinity...

   An upper trough  over the upper Great Lakes to the Mid-South area
   will shift eastward toward the Appalachians through Friday morning.
   This will result in around 30-35 kt southwesterly mid/upper level
   flow overspreading parts of the Carolinas into the Chesapeake
   Bay/Mid-Atlantic vicinity. A very moist airmass will be in place,
   with dewpoints generally in the upper 60s to low 70s F. Strong
   heating will result in steepening low level lapse rates, and MLCAPE
   from 1000-2500 J/kg is forecast across the region. Midlevel lapse
   rates will be poor, and effective shear around 25-35 kt, limiting
   updraft organization/longevity. Nevertheless, PW values approaching
   2 inches and sufficient instability/shear should result in clusters
   of strong storms capable of isolated wet microbursts and locally
   damaging wind gusts.

   ..Leitman.. 08/05/2020

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