SPC AC 200727

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0227 AM CDT Wed May 20 2020

   Valid 221200Z - 231200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
   AND EVENING ACROSS PARTS OF NORTHWEST TEXAS...MUCH OF
   OKLAHOMA...SOUTHEASTERN KANSAS...SOUTHWESTERN MISSOURI AND
   NORTHWESTERN ARKANSAS...

   ...SUMMARY...
   Strong to severe thunderstorms may impact southern portions of the
   central Plains into parts of the Ozark Plateau Friday, accompanied
   by at least some risk for severe weather.

   ...Synopsis...
   The remnants of a cut-off low appear likely to become increasingly
   progressive during this period, migrating from the middle Ohio
   Valley toward the Mid Atlantic coast, as upstream short wave
   troughing emerging from the Southwest progresses into middle to
   upper portions of the Mississippi Valley.

   Farther upstream, large-scale troughing will be maintained across
   much of the Intermountain West and Rockies, with some amplification
   as a vigorous embedded short wave trough digs from the northern
   intermountain region through the Great Basin, before turning
   eastward into the Rockies.  Ahead of the this feature, mid-level
   short wave ridging is expected to build across much of the higher
   Plains, accompanied by a new plume of warm elevated mixed-layer air.

   While surface troughing deepens across the higher Plains, higher
   moisture content is forecast to be advected eastward toward the
   mid/upper Mississippi Valley, ahead of the aforementioned preceding
   short wave trough, and another progressing from the eastern Dakotas
   into northwestern Ontario and Minnesota.  However, in the wake of
   these perturbations, low-level moisture will increase further on
   continuing southerly return flow into the southern Plains.  Surface
   dew points may increase to near 70 F across and north of the Red
   River Valley, contributing to large CAPE beneath steep mid-level
   lapse rates.

   ...Southern Plains into Ozark Plateau...
   A belt of moderately strong (40+ kt) southwesterly 500 mb flow may
   overspread the region, to the south of the short wave trough
   emerging from the Southwest.  Coupled with the moderate to strong
   boundary-layer destabilization, including CAPE of 2000-3000+ J/kg)
   the environment may become at least conditionally supportive of
   organized severe storms.

   It is possible that the remnants of an overnight cluster of
   thunderstorms spreading east-southeastward out of the higher Plains
   could re-intensify during the day while spreading across southern
   Kansas and Oklahoma, aided by inflow of increasingly unstable air. 
   Otherwise, warm advection in its wake, and perhaps low-level
   convergence along a trailing outflow boundary, particularly near a
   possible intersection with the dryline, may support renewed vigorous
   thunderstorm development across parts of central and western
   Oklahoma into northwest Texas late Friday afternoon and evening.
   Isolated supercells are possible initially,  with activity probably
   tending to grow upscale quickly into one or more organizing
   clusters, accompanied by potential for damaging wind gusts, in
   addition to large hail.

   ..Kerr.. 05/20/2020

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