SPC AC 251727

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 PM CDT Thu Jun 25 2020

   Valid 261200Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   SOUTHEAST WI AND CENTRAL/SOUTHERN LOWER MI...

   ...SUMMARY...
   A line of severe thunderstorms is expected from southern Wisconsin
   into Lower Michigan Friday afternoon and evening. Additional strong
   to severe storms are possible from the Mid Mississippi Valley
   through the central Plains into the central High Plains.

   ...Upper Midwest/Lower Great Lakes...
   A warm front is forecast to extend from northern IL northwestward
   across southwest and west-central WI into east-central/northeast MN
   early Friday morning. Scattered thunderstorms, aided by enhanced
   low-level flow throughout the eastern periphery of an approaching
   upper trough, will likely be ongoing along and north this front,
   near an attendant surface low/triple point. The warm front over the
   region is expected to move northward/northeastward throughout the
   day as this weak low moves east-northeastward, bringing mid to upper
   60s dewpoints in to central/southern WI by early afternoon and into
   central/southern Lower MI by the late afternoon. Additional
   thunderstorm development (or possibly just reinvigoration of the
   early period storms) is expected as the low encounters the more
   moist and unstable boundary layer downstream. Mesoscale forcing for
   ascent will be provided by the surface low, with the approaching
   upper trough providing additional large-scale ascent.

   Expectation is for this forcing to result in quick thunderstorm
   development once the air mass destabilizes. Linear character to the
   forcing for ascent combined with the presence of moderate to strong
   westerly flow aloft is expected to promote quick upscale growth into
   an organized convective line. Consequently, a corridor of higher
   wind gust potential is expected along and just south of the warm
   front. Based on current guidance, the corridor appears to be mostly
   likely from southeast WI into central/southern Lower MI.
   Additionally, the moderate to strong mid-level flow will result in
   enough low-level vertical shear to support transient/brief
   line-embedded/QLCS tornadoes. Hail is also possible, particularly
   with any early, more cellular storms or as a result of storm
   mergers/interactions within the line.

   ...Mid MS/Mid MO Valleys into the Central Plains...
   Moderate instability is forecast to be in place from the Mid MS
   Valley into the central Plains ahead of the approaching cold front.
   Vertical shear will weaken with southwestward extent, but abundant
   low-level moisture (i.e. dewpoints in the upper 60s/low 70s) and
   steep mid-level lapse rates (particularly across the central Plains)
   will help support strong updrafts capable of both large hail and
   damaging downburst winds.

   ...Central/Southern High Plains into the Central Plains...
   Upslope flow behind the cold front will help support isolated to
   scattered thunderstorm developing across the Front Range late Friday
   afternoon. Instability will be modest, but easterly/northeasterly
   surface wind beneath westerly flow aloft will contribute to moderate
   vertical shear and the potential for a few supercells. Large hail is
   possible, particularly with initial storm development, but the
   primary threat is expected to be strong wind gusts as the high-based
   storms move off the terrain. An isolated landspout-type tornado also
   cannot be ruled out, though potential for greater tornado risk
   should remain limited by a dry/deep boundary layer.

   Given the presence of a slow-moving (maybe even stalled) front
   across the region, continued eastward propagation of a more
   organized linear system into western/central KS is possible. This
   scenario is most likely if storms can persist long enough into the
   evening for lift/moisture to be augmented by the low-level jet.
   Enough guidance is beginning to show this scenario to introduce
   higher wind/hail probabilities across the central High Plains and
   central Plains. 

   ...East Texas and the Arklatex vicinity...
   Model forecasts of a weak upper low drifting northward across East
   Texas will likely support an increase in afternoon storm development
   across the Texas/Arkansas/Louisiana vicinities.  Slightly enhanced
   southerly low-level flow ahead of the low may promote rather fast
   northward storm motion, possibly resulting in a stronger wind gust
   or two.

   ..Mosier.. 06/25/2020

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