SPC AC 111651

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1151 AM CDT Sat Jul 11 2020

   Valid 111630Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO TONIGHT FOR SOUTHERN AND EASTERN KS...NORTHERN OK...WESTERN
   MO...AND EXTREME NORTHWESTERN AR...

   ...SUMMARY...
   Scattered severe thunderstorms with very large hail and damaging
   winds are expected this afternoon into tonight for parts of
   southeastern Kansas, northern Oklahoma, western Missouri, and
   northwestern Arkansas, with other severe storms expected across the
   Midwest.

   ...Western MO/KS/OK mid-afternoon into tonight...
   A surface cold front will move southeastward across KS/MO/IL this
   afternoon to near the KS/OK border by this evening. A belt of
   stronger midlevel flow (~50 kt) will develop southeastward along the
   corridor from roughly northwestern NE to eastern KS/western MO and
   overspread parts of the surface warm sector.

   Strong surface heating will occur today beneath a plume of midlevel
   lapse rates in excess of 8 C/km extending over OK/KS.  Initial
   thunderstorm development is expected by mid-late afternoon along the
   front in northeast KS, and storms will subsequently increase and
   spread south-southeastward across eastern KS/extreme western MO.
   Additional storm development is expected farther west-southwest
   along the boundary later this afternoon/evening as deep mixing with
   hot surface temperatures removes convective inhibition near the
   southern KS/northern OK border. 

   Large buoyancy (MLCAPE of 3000-4000 J/kg) with steep mid-level lapse
   rates, effective bulk shear of 40-50 kt, and relatively
   long/straight hodographs will favor splitting intense supercells
   capable of producing very large hail. Upscale growth into multiple
   clusters or line segments is also possible later this evening, when
   damaging winds will become a greater threat. A few significant wind
   gusts can be expected given the steep lapse rate profiles, organized
   storm structures, and strong downdraft potential with large DCAPE
   (near 1500 J/kg).

   ...Midwest including southern MN and IA/IL...
   An east/southeastward-moving shortwave trough is noted over the far
   eastern Dakotas/west Minnesota at midday. The region will be
   influenced by a seasonably strong belt of northwesterly aloft aloft,
   with multiple corridors of severe weather expected to unfold later
   this afternoon and tonight across a relatively broad region.

   First, a small storm cluster continues southeastward at midday
   generally near the Quad Cities of eastern Iowa/northwest Illinois.
   This storm may persist, with other outflow/differential
   heating-influenced development within an increasingly unstable air
   mass across Illinois and eventually western Indiana. A combination
   of severe wind/hail is possible.

   Farther west/northwest, a seemingly more certain/focused severe risk
   is expected to occur initially across southern Minnesota/northern
   Iowa. The boundary layer continues to quickly destabilize across the
   region, particularly across Iowa on the western fringe of the early
   day small MCS and related outflow. Mid-level lapse rates and
   deep-layer vertical shear will support a mix of supercells and
   southeastward-moving linear clusters capable of producing large hail
   and damaging winds (and combined wind-driven large hail),
   particularly across north-central/east-central Iowa and eventually
   into western Illinois/eastern Missouri.

   ...PA/NY into western New England this afternoon/evening...
   A mid-level shortwave trough will continue to move
   east-northeastward over Pennsylvania/New York through this evening.
   As is already beginning to occur, related forcing for ascent and a
   surface trough/weak front will initially focus thunderstorm
   development in a broken arc from western New York to east-central
   Pennsylvania, with storms spreading eastward through the
   afternoon/evening. Surface heating in cloud breaks and
   boundary-layer dewpoints of 68-70 F will support MLCAPE near 1000
   J/kg.  Though mid-level lapse rates will be poor, steepening of
   low-level lapse rates and a modest increase in midlevel flow with
   the approaching shortwave trough could support occasional
   strong/damaging wind gusts this afternoon and evening.

   ..Guyer/Bentley.. 07/11/2020

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