SPC AC 221237

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0737 AM CDT Mon Jun 22 2020

   Valid 221300Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHERN GREAT
   PLAINS...

   ...SUMMARY...
   Scattered severe thunderstorms with hail and wind will be possible
   from late afternoon into tonight over the southern Great Plains.
   Isolated severe storms will also be possible across portions of the
   central Great Plains, Midwest, Deep South, Mid-Atlantic, and south
   Florida.

   ...Southern Great Plains...
   Convective outflow from a decaying MCS near the Red River and
   northeast TX has surged as far south as the TX South Plains, Concho
   Valley, and east-central TX. Mid to late afternoon storm development
   should be focused in two areas, influenced by this boundary.
   Low-level upslope flow north of the boundary over the High Plains
   will aid in scattered storm development off the higher terrain.
   Deeply mixed thermodynamic profiles amid 25-40 kt 500-300-mb
   northwesterlies will support initial high-based supercells with a
   primary threat of large hail early. Convection should tend to
   consolidate as it spreads east-southeast across the Panhandles and
   northwest TX during the evening, likely aided by a ribbon of
   low-level easterlies. This should yield an uptick in severe wind
   coverage during the early to mid-evening. While increasing MLCIN
   should be detrimental to the southern extent of severe wind
   potential, isolated to scattered severe wind gusts may persist
   tonight across western north TX with an eastward-propagating MCS
   north of the large-scale outflow boundary. Severe hail will also be
   possible overnight farther east near the Red River Valley with any
   low-level warm-advection-driven convection.

   Convective development along the outflow boundary farther east
   across TX during the late afternoon to early evening is more
   uncertain. While intense boundary-layer heating will occur to the
   south of the boundary and some convergence will exist along it, the
   region will lie in the wake of the MCV moving into the Lower MS
   Valley. If storms do form, they would likely pose a mixed hail and
   wind threat given the presence of steep lapse rates and large
   buoyancy (MLCAPE 2500-4000 J/kg). Weakening winds with height from
   the mid to upper-levels suggest a dominant cluster mode.

   ...IL and eastern portions of IA/MO...
   Considered an upgrade to Slight Risk within this portion of the
   Mid-MS Valley/Midwest, but uncertainties in the quality of
   boundary-layer destabilization render deference.

   A weak surface cyclone over southwest IA should track into northern
   IL ahead of an upper-level shortwave trough ejecting east from the
   Mid-MO Valley. While low-level flow will probably remain modest,
   adequate mid/upper-level flow will exist for storm organization. The
   main uncertainty is how unstable the air mass will be this afternoon
   owing to weak mid-level lapse rates and relatively pervasive
   early-day convection. Storm-scale guidance such as the HRW-ARW and
   HRW-NSSL appear to be more accurately simulating the extent of
   ongoing convection and are more subdued with the degree of
   convective intensity later today. While 09Z and earlier HRRR runs,
   which appeared underdone with ongoing convection, are suggestive of
   a QLCS evolving which would yield a more focused corridor of
   damaging wind potential. 

   ...Lower MS Valley/Mid-South...
   An MCV near the OK/AR border, that emanated out of a decaying MCS,
   should move east today overtaking/merging with a nearly stationary
   MCV in southeast AR. A confined belt of enhanced low/mid-level
   southwesterlies should be present this afternoon. However,
   destabilization will likely be more pronounced well south/southwest
   of the MCV track given how far south the large-scale convective
   outflow has surged in eastern TX and the Ark-La-Tex, in addition to
   weak mid-level lapse rates to the east. Still, have added a low
   tornado probability given the conditional risk. Otherwise, isolated
   damaging winds should be the main threat. 

   ...Eastern NE/Mid-MO Valley...
   Mid-level perturbations over eastern MT and central SD, embedded
   within northwest flow should aid in isolated to scattered storm
   development this afternoon. The lack of steeper mid-level lapse
   rates should be a limiting factor to a greater severe risk. But
   isolated marginally severe hail and strong wind gusts appear
   possible with any storms that can form in this regime.

   ...Mid-Atlantic...
   An MCV over OH will drift east with afternoon scattered storms
   expected near and south of this feature. While buoyancy should
   become moderate given robust boundary-layer heating and mid to upper
   60s surface dew points, weak flow throughout the troposphere
   suggests pulse to perhaps loosely organized multicells should
   dominate. Microbursts producing strong gusts may yield localized
   tree damage.

   ...South FL...
   A few storms capable of producing wet microbursts and perhaps
   marginally severe hail should develop at peak afternoon heating
   along sea breeze boundaries. Large buoyancy with MLCAPE of 2500-3500
   will be the primary supporting factor as weak tropospheric winds
   suggest pulse to loosely organized multicells should prevail.

   ..Grams/Kerr.. 06/22/2020

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