SPC AC 111245

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0745 AM CDT Sat Jul 11 2020

   Valid 111300Z - 121200Z

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

   ...SUMMARY...
   Scattered severe thunderstorms with very large hail and damaging
   winds are expected this afternoon into early tonight for parts of
   southeastern Kansas, northeastern Oklahoma, western Missouri, and
   northwestern Arkansas.

   ...Western MO/KS/OK mid afternoon into tonight...
   A midlevel shortwave trough over ND this morning will move
   southeastward toward the middle MS Valley tonight.  This midlevel
   trough will be accompanied by a surface cold front which will move
   southeast across KS/MO/IL this afternoon to near the KS/OK border by
   this evening.  A secondary belt of stronger midlevel flow (~50 kt)
   will develop southeastward along the corridor from roughly
   northwestern NE to eastern KS/western MO (as suggested by water
   vapor imagery), and overspread parts of the surface warm sector.

   Much of the overnight convection has dissipated (aside from
   relatively new elevated storm development across southeast KS - see
   MD 1182 for additional information), with a remnant MCV now moving
   southeastward over northwest MO.  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 spread southward across eastern KS/extreme western
   MO.  Additional storm development is expected farther 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 midlevel lapse rates, effective bulk shear of 40-50
   kt, and relatively long/straight hodographs will favor splitting
   supercells capable of producing very large hail.  Upscale growth
   into multiple clusters or line segments is also possible later this
   evening into early tonight, when damaging winds will become a
   greater threat.  A few significant gusts can be expected given the
   steep lapse rate profiles, organized storm structures, and strong
   downdraft potential with large DCAPE (near 1500 J/kg).

   ...IA to IL today into early tonight...
   The primary midlevel shortwave trough will move over MN the first
   part of the day, IA this afternoon, and IL this evening into
   tonight.  Some continuation of the ongoing convection now across
   eastern ND/northwestern MN, or over southeastern MN, is expected
   through the afternoon.  Gradual intensification of the storms will
   occur as the low levels warm in advance of the storms across
   southern MN/IA by early afternoon, and sufficient buoyancy will
   remain to sustain the storms into northern IL through late evening. 
   Midlevel lapse rates and deep-layer vertical shear will not be quite
   as favorable compared to the Enhanced risk area, but still
   sufficient for a mix of supercells and clusters/line segments
   capable of producing large hail and damaging winds.

   ...PA/NY into western New England this afternoon/evening...
   A midlevel shortwave trough will move eastward over PA/NY through
   this evening.  Forcing for ascent in advance of the trough, and a
   surface trough/weak front, will focus thunderstorm development in a
   broken arc from western NY to central PA near midday, and storms
   will spread 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 midlevel lapse rates will be poor,
   steepening of low-level lapse rates and a modest increase in
   midlevel flow with the approaching midlevel trough could support
   occasional strong/damaging outflow gusts this afternoon/evening.

   ..Thompson/Broyles.. 07/11/2020

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