SPC AC 111950

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0250 PM CDT Sat Jul 11 2020

   Valid 112000Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
   OKLAHOMA...CENTRAL/EASTERN KANSAS...WESTERN MISSOURI...AND FAR
   NORTHWESTERN ARKANSAS...

   ...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.

   ...20Z Outlook Update...
   Primary change to the ongoing convective outlook was to add a small
   10% significant hail area ahead of convection migrating
   southeastward across Minnesota/Iowa.  Baseball sized hail was
   recently reported from a storm near the Minnesota/Iowa border area. 
   Favorable storm mode, steep lapse rates aloft, and strong,
   unidirectional shear profiles could favor additional significant
   hail reports before storms congeal further into linear segments.  2%
   tornado probabilities were also extended southeastward along an
   outflow boundary from east-central Iowa into north-central Illinois
   in the event that storms favorably interacting with this boundary
   acquire brief rotation.

   Farther east, strong to severe storms in northwestern Indiana were
   moving southeastward along the leading edge of a cold pool.  These
   storms were moving 330/30kt and on their current pace, should impact
   the Indianapolis Metro Area around 21Z-22Z or so.  The Slight risk
   (driven by convective wind probabilities) were expanded slightly
   eastward to account for a potential threat in that area.

   Outside of minor adjustments to general thunderstorm areas, the
   remainder of the outlook is unchanged.  Clusters of thunderstorms
   are expected to migrate south/southeastward across Kansas/northern
   Oklahoma/western Missouri and also from Minnesota/Iowa into northern
   Illinois later tonight.

   ..Cook.. 07/11/2020

   .PREV DISCUSSION... /ISSUED 1151 AM CDT Sat Jul 11 2020/

   ...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.

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