SPC AC 280059

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0759 PM CDT Sat Jun 27 2020

   Valid 280100Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Severe thunderstorms with large hail and wind damage will be
   possible this evening across parts of the central and northern High
   Plains. A marginal severe threat will exist from parts of the
   central Plains eastward to the Mid-Atlantic and in the Southeast.

   ...Central High Plains...
   The latest water vapor imagery shows a subtle shortwave trough over
   the central Rockies. Scattered thunderstorms are located just ahead
   of the trough from eastern Colorado into southwest Nebraska. This
   convection is located on the western edge of a pocket of moderate to
   strong instability. The RAP shows MLCAPE in the 1500 to 2500 J/kg
   range across far eastern Colorado and western Kansas. Due to the
   instability, the ongoing cluster of storms is expected to be
   sustained for much of the evening. RAP forecast soundings across
   much of the central Plains show moderate deep-layer shear and steep
   mid-level lapse rates. This should be enough for supercell
   development. Although supercells will be possible in areas where
   parameters are locally most favorable, multicell will be the more
   common storm type. For this reason, wind damage will be the primary
   threat but hail could occur with the stronger updrafts.

   ...Central Plains/Mid Mississippi Valley/Ohio Valley/Mid-Atlantic...

   The latest water vapor imagery shows a west-to-east flow pattern
   across much of the central and eastern U.S. A subtle shortwave
   trough is evident over eastern Missouri. Ahead of this feature, a
   couple clusters of strong to severe thunderstorms are ongoing. The
   first is in eastern Missouri and the second is from southern Indiana
   into northern Kentucky. The airmass in these two areas is moderately
   unstable according the RAP, with MLCAPE in the 1500 to 2500 J/kg
   range. Regional WSR-88D VWPs generally have 0-6 km shear in the 20
   to 30 kt range suggesting storm type will remain multicell. As
   low-level lapse rates remain steep over the next hour or two, a few
   damaging wind gusts will be possible. A marginal severe threat will
   also exist further east into the Ohio Valley and Mid-Atlantic but
   cell coverage should remain very isolated.

   ...Northeast Alabama/Georgia/South Carolina...
   The latest surface analysis shows an area of high pressure to the
   east of Florida with southerly flow to the west of the high across
   much of the Gulf Coast region. A moist airmass is located across the
   Southeast with dewpoints mostly from the upper 60s to the mid 70s F.
   This is resulting in moderate to strong instability across much of
   the region. Although deep-layer shear is relatively weak, low to
   mid-level lapse rates are steep. This suggests that a marginal wind
   damage threat will exist with the stronger multicells or pulse
   storms.

   ...Northern Rockies/Northern High Plains...
   The latest water vapor imagery shows an upper-level trough over the
   Pacific Northwest with west-southwesterly mid-level flow over the
   northern Rockies and northern High Plains. Ahead of the trough, a
   moist airmass is in place across the northern Rockies and northern
   High Plains the RAP is analyzing SBCAPE in the 1000 to 2000 J/kg
   range. Scattered thunderstorms are ongoing on the northern edge of
   the stronger instability from southwest Montana into north-central
   Montana. Regional WSR-88D VWPs across this area show 0-6 km shear
   generally from 45 to 55 kt suggesting the environment will support
   supercells and organized multicells this evening. The greatest
   severe threat should exist in central and northern Montana where the
   combination of parameters is maximized. Isolated large hail and wind
   damage will be the primary threats.

   ..Broyles.. 06/28/2020

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