SPC AC 241735

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1235 PM CDT Wed Jun 24 2020

   Valid 251200Z - 261200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   WESTERN NEBRASKA...SOUTH DAKOTA...SOUTHEAST NORTH DAKOTA AND WESTERN
   MINNESOTA...

   ...SUMMARY...
   Scattered strong/locally severe storms will be possible across parts
   of the north-central U.S. Thursday afternoon and evening. Locally
   damaging wind gusts and hail will be the main hazard with these
   storms.

   ...North-central States...

   A shortwave trough over the northern Rockies will develop eastward
   across the northern/central Plains on Thursday, breaking down an
   upper ridge over the region. At the surface, a weak low over
   northern ND will shift eastward through the period. A surface trough
   will extend southwestward from the low to near the eastern WY border
   and into eastern CO. A trailing cold front will then move
   east/southeast across the region from early afternoon into early
   Friday morning. 

   Southerly low level flow will result in 60s F dewpoints across
   central and eastern portions of ND/SD/NE, with 50s F dewpoints
   further west toward WY/CO. Strong heating ahead of the cold front
   will aid in strong destabilization (MLCAPE 2500-4000 J/kg) by early
   afternoon. While some weak capping is expected due to warm
   temperatures around 850-700 mb beneath the upper ridge, this should
   easily erode as strong forcing for ascent overspreads the area and
   modest cooling aloft occurs with the approach of the trough. The
   current expectation is that thunderstorms will develop by mid
   afternoon along the pre-frontal surface trough from eastern ND
   through central and western SD and western NE. While deep-layer flow
   is not expected to be strong, veering winds with height will result
   in 35-45 kt effective shear, supporting organized clusters and
   supercells.  Any discrete cells will be capable of large hail as
   strong instability will support robust updrafts amid steep midlevel
   lapse rates around 7.5-8 C/km. Otherwise, steep low level lapse
   rates and inverted-v sub-cloud thermodynamic profiles will favor
   strong downburst winds. Low level shear will remain weak, with
   limited effective SRH noted in most guidance. While a brief tornado
   can not be ruled out with any storms interacting with outflow
   boundaries, etc, tornado potential appears fairly low. 

   Additional strong storms will initiate over the higher terrain of
   WY/CO during the afternoon and shift eastward over the High Plains
   through the evening. A deeply-mixed boundary layer with steep low
   level lapse rates will also support strong downburst winds across
   the High Plains of eastern WY/northeast CO into western NE. 

   ...Carolinas into southeast VA...

   Numerous small-scale disturbances embedded within broad mid-level
   cyclonic flow over the east are progged to rotate across the central
   Appalachians/mid-Atlantic region and into the Carolinas Thursday.
   Convection -- some of it likely ongoing at the start of the period
   -- is expected across the discussion area, perhaps limiting
   destabilization across some areas.  However, with 35 to 45 kt
   westerly mid-level flow atop the area, any new afternoon convective
   development would have the potential for fast eastward storm motion
   and some potential for locally gusty/potentially damaging winds.

   ..Leitman.. 06/24/2020

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