SPC AC 271623

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1123 AM CDT Tue Apr 27 2021

   Valid 271630Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
   TONIGHT OVER PARTS OF THE SOUTHERN PLAINS...CENTRAL HIGH
   PLAINS...AND WISCONSIN....

   ...SUMMARY...
   Clusters of strong to severe thunderstorms will affect parts of the
   southern Plains, central High Plains, and Wisconsin this afternoon
   and tonight.

   ...Central Plains...
   A broad upper trough is present over the western states today, with
   relatively strong southwesterly midlevel flow across the Plains and
   Midwest states.  While widespread 50/60s dewpoints and steep lapse
   rates are in place across this region, widespread clouds and a
   strong capping inversion will limit convective development and
   increase uncertainty when/where storms will intensify.  

   Most 12z CAM guidance is in agreement that scattered thunderstorms
   will develop by mid-afternoon over parts of western north TX in
   vicinity of the dryline. These storms will track northeastward
   across OK during the day, where ample CAPE (MLCAPE values over 1500
   J/kg) will promote a risk of large hail and damaging winds.  These
   storms may track into parts of southeast KS and western MO this
   evening before slowly weakening.

   In the wake of this activity, the dryline may be the focus for
   further convective initiation this evening over west TX as weak
   large-scale lift overspreads the area.  Low-level shear profiles
   will be stronger by this time, and presence of remnant boundaries
   from earlier convection may increase the risk of supercells capable
   of very large hail and a tornado or two.  These storms will also
   spread into OK through the late evening.

   ...Northeast CO into KS/NE...
   A surface cold front currently lies from east-central CO eastward
   into western KS.  Northeasterly low-level winds on the north side of
   the boundary are transporting 40s dewpoints westward into the high
   Plains, where thunderstorm development is expected by early
   afternoon.  Storms will likely intensify as they move eastward into
   a progressively more unstable air mass.  Cold temperatures aloft,
   steep lapse rates, and sufficient vertical shear for supercells will
   pose a risk of large hail and perhaps a tornado.  Storms will track
   into western/central NE and northwest KS during the late
   afternoon/evening with a continued severe threat.

   ...South TX...
   Southeasterly low-level winds will continue to transport rich Gulf
   moisture up the Rio Grande valley and up against the adjacent
   Mexican mountains.  Thunderstorms are expected to form in the higher
   terrain by late afternoon and track across the border into south and
   central TX.  These supercell storms will pose a risk of very large
   hail, damaging winds, and a few tornadoes through the evening.

   ...WI...
   A cold front stretches across south-central WI today.  Periods of
   scattered thunderstorms will occur today and tonight over this area,
   with CAM guidance focusing on this evening as the most active
   period.  Sufficient elevated CAPE above the cold/stable
   surface-layer will pose a risk of hail in the strongest cells
   throughout the period.

   ..Hart/Squitieri.. 04/27/2021

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