SPC AC 300546

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1246 AM CDT Sun Jun 30 2019

   Valid 301200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   ILLINOIS AND WISCONSIN WESTWARD INTO EASTERN WYOMING...

   ...SUMMARY...
   Strong to severe storms are possible today from the upper
   Mississippi Valley and western Great Lakes into eastern Wyoming,
   with damaging wind and hail the main threats.

   ...Upper Mississippi Valley region into the northern Plains...
   A mid-level shortwave trough will move east across Manitoba into
   western Ontario during the period while a cold front pushes
   southeast across the north-central states and becomes stationary in
   western NE.  A warm front will become aligned from MN into the OH
   Valley.

   There is considerable uncertainty for the forecast over the Midwest
   portion of the Slight Risk with storm-scale/outflow influences
   largely dictating the potential severe coverage/timing due primarily
   to a possible MCS.  Current thinking is an MCS will be ongoing over
   parts of the Upper Midwest with a risk for damaging winds. 
   Downstream of this thunderstorm cluster over southern WI into IL,
   the warm sector will become very unstable during peak heating with a
   plume of steep (7-7.5 C/km) 700-500mb lapse rates overspreading
   low-mid 70s F dewpoints and contributing to 3000-5000 J/kg MLCAPE. 
   The latest HREF guidance strongly suggests storms will reintensify
   on the leading edge of outflow during the midday to afternoon in an
   environment with weak deep-layer shear.  Other storms may develop
   along cold front across southern MN into southeast SD during the
   afternoon.  Wind profiles with weak vertical shear will favor
   multicells, but the thermodynamic environment will promote a threat
   for damaging wind and large hail. 

   ...Northern High Plains...
   Easterly post-frontal upslope flow will develop from southeast MT
   into northeast WY with dewpoints generally in the 50s to around 60F.
   A plume of steeper lapse rates will persist over this region and the
   atmosphere should become moderately unstable as low clouds mix out
   from the west. Storms should develop during the afternoon over the
   higher terrain and spread east into the High Plains where wind
   profiles with 30-40 kt effective shear will support some supercell
   structures. Large hail and isolated damaging wind will be possible
   from late afternoon into mid evening.

   ...Southern New England...
   Cold temperatures aloft associated with an amplifying upper trough
   will overspread this region generally along and north of a cold
   front that should move through southern New England the first half
   of the day.  Diabatic warming will further destabilize the
   atmosphere with 500-1000 J/kg MLCAPE possible.  Gusty winds are
   possible with the strongest storms from late morning into mid
   afternoon.

   ..Smith/Nauslar.. 06/30/2019

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