SPC AC 220559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Mon Jun 22 2020

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS TO THE ARKLATEX...

   ...SUMMARY...
   Isolated to scattered severe thunderstorms capable of producing
   damaging winds and large hail will be possible today across parts of
   the southern Plains into the lower/mid Mississippi Valley. Other
   strong to severe storms may also occur over portions of the central
   Plains, Midwest, Southeast, Mid-Atlantic, and south Florida.

   ...Synopsis...
   A large-scale upper trough/low will move slowly eastward across
   central Canada, the upper MS Valley/Midwest, and Great Lakes regions
   today. Multiple convectively enhanced vorticity maxima will move
   generally east-northeastward within this mid-level flow regime
   across the central/eastern CONUS through the period. Some of these
   vorticity maxima will have MCVs associated with them, which may
   serve to focus strong/severe storm potential. At the surface, a weak
   low initially over IA should develop northeastward across southern
   WI during the afternoon. A cold front trailing southwestward from
   this low should move slowly southeastward across the mid MS Valley
   and southern Plains through the period.

   ...Southern Plains...
   An MCS ongoing early this morning across western/central OK should
   weaken later today as it continues to move southward and a low-level
   jet gradually lessens. It appears increasingly probable that renewed
   storm development this afternoon and evening should focus along an
   outflow boundary from this early day convection, as well as in a
   low-level upslope flow regime across the southern High Plains. There
   remains considerable uncertainty regarding the eventual location of
   this outflow boundary by late afternoon/early evening, but most
   guidance suggests it should be located somewhere in the vicinity of
   north/central TX towards the ArkLaTex. The likelihood for robust
   convective development along the weak cold front near the KS/OK
   border has lessened somewhat owing to convective overturning from
   the ongoing MCS. Accordingly, 15% severe hail/wind probabilities
   have been generally adjusted/expanded southward.

   Greatest confidence in convective initiation by mid/late afternoon
   is across the higher terrain of eastern NM into the TX/OK Panhandles
   in the low-level upslope flow regime. Somewhat enhanced mid-level
   northwesterly flow and steep mid-level lapse rates will support a
   threat for large hail with initial storm development. There is some
   signal for clustering/upscale growth of this activity across the
   southern High Plains through the evening, with a potentially
   increased severe wind threat. Additional storm development along the
   outflow boundary appears possible this afternoon/evening, but is
   less certain. If storms do form, they would likely become severe
   with both a hail and wind threat given the presence of strong to
   very strong instability (MLCAPE 2500-4500+ J/kg) and marginal
   deep-layer shear.

   ...Mid/Upper Mississippi Valley into the Midwest and Great Lakes...
   At least some airmass recovery is expected along/ahead of a weak
   cold front this afternoon in the wake of ongoing storms across
   IA/WI. Storms should redevelop in a somewhat favorable kinematic
   environment as a shortwave trough embedded within the larger-scale
   flow moves over the mid/upper MS Valley and Midwest. Marginal
   effective bulk shear values may limit storm organization to some
   degree, but multicell clusters capable of producing both damaging
   winds and large hail appear possible. At this point, there is not
   enough confidence in a more focused corridor of damaging wind
   potential to include greater severe probabilities.

   ...Lower Mississippi Valley into the Southeast...
   An MCV emanating from the ongoing MCS across OK early this morning
   should move east-northeastward across the lower MS Valley and
   Southeast today in tandem with a mid-level vorticity maximum. There
   should be enough flow at low/mid levels and large-scale lift
   associated with these features to provide occasional organization
   with any storms that can form through the afternoon and early
   evening. Latest guidance has increased overall convective coverage
   across this area, with at least scattered storms probable. Mainly an
   isolated damaging wind threat could materialize with this activity
   as it spreads east-northeastward through the early evening.

   ...Central Plains...
   Isolated storm development appears possible along/ahead of a
   reinforcing cold front from far southeastern SD into parts of
   central/eastern NE this afternoon. A northwesterly flow regime aloft
   and cool mid-level temperatures may support at least weak
   destabilization in the presence of 25-35 kt of effective bulk shear.
   Isolated instances of marginally severe hail and strong to severe
   wind gusts appear possible with any storms that can form in this
   regime.

   ...Mid-Atlantic...
   Storms should increase in coverage and intensity this afternoon as a
   MCV and related mid-level vorticity maximum move northeastward
   across the Mid-Atlantic region and vicinity. Although low to
   mid-level flow will remain rather modest, there should be enough
   shear coupled with 1500-2500 J/kg of MLCAPE to support some storm
   organization. Strong to locally damaging winds should be the main
   threat, although marginally severe hail cannot be ruled out.

   ...South Florida...
   A few storms capable of producing isolated strong/gusty winds and
   perhaps hail should develop by peak afternoon heating across parts
   of south FL along localized sea breeze boundaries. Relatively cool
   mid-level temperatures and the presence of modestly steepened
   mid-level lapse rates may support some storm organization, even
   though low/mid-level winds will remain modest.

   ..Gleason/Squitieri.. 06/22/2020

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