SPC AC 210559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Sun Jun 21 2020

   Valid 211200Z - 221200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
   KS AND NORTHERN OK...

   ...SUMMARY...
   Scattered severe storms capable of producing mainly large hail and
   damaging winds appear likely this afternoon and evening across a
   portion of the southern and central Plains into the Upper Midwest.
   The greatest concentration of severe storms should occur across much
   of Kansas into northern Oklahoma.

   ...Kansas into the Southern Plains and Lower Mississippi Valley...
   A small cluster of mainly elevated storms capable of producing
   isolated hail and gusty winds may be ongoing at the start of the
   period later this morning along/near the Red River in southern
   OK/north TX. This activity should weaken some through the morning as
   the low-level jet gradually lessens. However, a MCV generated by
   these storms may support renewed convective development across parts
   of the ArkLaTex and lower MS Valley this afternoon. If this occurs,
   then isolated strong to damaging winds appear possible across these
   regions.

   A low-amplitude shortwave trough embedded within a
   west-northwesterly flow regime aloft will move over the central
   Plains by this afternoon. Strong heating is expected to occur east
   of surface lee trough/dryline across the central/southern High
   Plains as low-level moisture also gradually increases. A pronounced
   EML will be present over much of the central/southern High Plains,
   which will help support moderate to very strong instability (MLCAPE
   2000-4500 J/kg) east of the dryline by peak afternoon heating. Even
   though the mid-level flow associated with the approaching shortwave
   trough is not forecast to be overly strong, it should still be
   sufficient (30-40 kt of effective bulk shear) for robust storm
   organization.

   Current expectations are for rapid severe storm development across
   western KS and vicinity by early to mid afternoon. These storms
   should quickly become severe, with an initial threat for scattered
   large to very large hail given enough shear to support a mix of
   supercells and multicells. With time, storms should congeal and grow
   upscale into a well-organized bow as a southerly low-level jet
   strengthens this evening across the southern/central Plains. At
   least scattered severe/damaging winds should become the main threat
   as this mode transition occurs across central/eastern KS into
   northern OK. Some uncertainty remains regarding the southward and
   eastward extent of the severe wind threat across OK and the Ozarks.
   A relatively brief window for a couple tornadoes also appears
   possible early this evening across parts of south-central KS into
   northwestern OK as low-level shear increases and storm mode probably
   remains semi-discrete.

   ...Nebraska into the Upper Midwest...
   Another vorticity maximum should rotate through the base of an upper
   low centered over southern Canada today. As this feature moves over
   the northern Plains into the upper MS Valley, moderate to
   potentially strong destabilization is forecast to occur ahead of a
   weak cold front, with MLCAPE of 1500-2500+ J/kg likely. Some
   increase in deep-layer shear is also expected by mid afternoon.
   Storms will likely form along/ahead of the front from central NE
   into southern MN, with a mix of supercells and multicells possible.
   Both large hail and damaging winds should be the main threat as
   these storms spread eastward into the Upper Midwest through the
   evening.

   ...Ohio and Tennessee Valleys...
   A convectively enhanced vorticity maximum with associated MCV is
   forecast to move northeastward across parts of the OH/TN Valleys
   through the day. Diurnal heating ahead of this feature combined with
   a moist airmass should support around 1000-1500 J/kg of MLCAPE by
   early afternoon. Although mid-level flow should remain relatively
   modest, there may be enough veering/strengthening with height to
   support multicell clusters with mainly an isolated damaging wind
   threat.

   ..Gleason/Squitieri.. 06/21/2020

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