SPC AC 061234

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0734 AM CDT Wed Jun 06 2018

   Valid 061300Z - 071200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MAINLY THIS
   AFTERNOON AND EVENING FROM CENTRAL IA TO WESTERN KS...AND ACROSS
   CENTRAL AND NORTH CENTRAL WY...

   ...SUMMARY...
   Thunderstorms will be capable of producing large hail and damaging
   winds in several corridors later today into early tonight across
   western Kansas and vicinity, Iowa, and Wyoming.

   ...Southwestern NE to northwestern OK late this afternoon through
   early tonight...
   Strong surface heating/mixing along the west edge of the richer
   low-level moisture and low-level upslope flow will support
   thunderstorm development late this afternoon/evening from eastern CO
   into western KS and southwest NE.  An MCS should emerge from this
   initial activity and propagate eastward along and just south the
   slow-moving front in NE and northwest KS.  Some large hail will be
   possible, though damaging outflow winds will become the main threat
   as a result of steep low-level lapse rates/strong downdraft
   potential and large buoyancy.  A separate MCS corridor will be
   possible from western KS southeastward toward northwest OK late this
   evening into early tonight.  Here, initial high-based convection
   near the CO/KS border will encounter increasingly large buoyancy
   (MLCAPE of 3000-4000 J/kg) while spreading into western KS.  Some
   supercell structures will be possible initially given the large
   CAPE/steep lapse rate environment with effective bulk shear of
   35-40kt.  The storms should then grow upscale through
   mergers/outflow interactions and then forward propagate into the
   strengthening low-level southeasterly/southerly flow this evening
   along the corridor of strong buoyancy.  The storms could make it as
   far southeast as northwestern OK before the damaging wind/hail
   threats begin to diminish overnight.  Will add significant severe
   areas for hail given some supercell potential and large CAPE/steep
   lapse rates, as well as for damaging winds given intense downdraft
   potential in the hybrid profiles with large CAPE atop a deeply mixed
   boundary layer, though uncertainties remain regarding storm coverage
   and evolution.

   ...IA to eastern NE through this evening...
   An MCS (with a well-defined MCV and cold pool) is moving
   southeastward across southern MN this morning, along a surface warm
   front and the instability gradient.  The outflow with this
   convection is well ahead of the somewhat diffuse synoptic cold
   front.  The convection has been weakening this morning and the
   outflow is expected to slow across central IA by midday.  Surface
   heating along the outflow boundary and south of the remnant MCS
   cloud shield, and a continued influx of 68+ F dewpoints from
   KS/southeast NE, will drive strong buoyancy this afternoon. 
   Additional thunderstorms should form mid-late afternoon across
   central IA along the remnant outflow, and subsequently move
   southward and develop westward toward eastern NE.  Deep-layer
   vertical shear will be sufficient for a mix of organized multicell
   clusters and/or marginal supercells, with an attendant threat for
   large hail and damaging winds.

   ...Central and northern WY this afternoon/evening...
   Water vapor imagery shows a midlevel shortwave trough moving
   north-northeastward toward southwestern UT this morning.  This
   trough will approach western WY this evening and interact with the
   west edge of relatively rich low-level moisture (55-60 F dewpoints
   now across central WY), within the upslope flow regime north of a
   slow-moving cold front.  Thunderstorm development is expected over
   the high terrain of the Wind River and Absaroka ranges by around mid
   afternoon, and storms will then spread northeastward toward the Big
   Horn Basin.  Moderate buoyancy (MLCAPE of 1500-2500 J/kg) and
   effective bulk shear of 30-40kt will be sufficient for supercells,
   though growth into a larger cluster is also expected this
   afternoon/evening.  Large hail will be possible with any initial
   supercells, with the threat transitioning more to damaging winds as
   upscale growth occurs.

   ..Thompson/Mosier.. 06/06/2018

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