SPC AC 161715

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1215 PM CDT Wed Aug 16 2017

   Valid 171200Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   LOWER MI...NORTHEAST IN AND NORTHWEST OH...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE SOUTHERN HIGH PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE OH VALLEY AND LOWER MI...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE SOUTHERN AND CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Thunderstorms, some severe, are expected across the Ohio Valley into
   lower Michigan. Scattered thunderstorms are also expected across the
   central and southern High Plains, where some severe storms are also
   possible.

   ...Synopsis...
   A well-defined, seasonally strong shortwave trough will progress
   through the upper Midwest and into the upper Great Lakes region,
   while maturing, during the period.  Consensus amongst the guidance
   suggests the surface low associated with this upper system will be
   near the central portions of the MN/WI border at 12Z Thursday, with
   an attendant cold front stretching from the low southward through
   central IA and then southwestward back through central OK and into
   the southern TX Panhandle. Another shortwave trough is expected to
   move quickly into the northern Plains tomorrow night.

   ...Middle MS Valley...OH Valley...Lower MI...
   Showers and thunderstorms will likely be ongoing at the beginning of
   the period within the WAA zone near the surface low across northern
   WI and upper MI. However, farther south, general expectation is for
   the portion of the front moving across the middle MS Valley to be
   mostly void of thunderstorm activity, largely a result of being
   displaced south of the strongest forcing for ascent but north of the
   better instability. A reinvigoration of thunderstorms is expected
   across lower MI and the central OH Valley as the cold front
   encounters the moist and diurnally destabilized airmass across the
   region. A predominately multicell mode is anticipated with possible
   embedded bowing structures contributing to occasional damaging wind
   gusts. Some isolated hail is also possible within the more organized
   storms. Relatively higher coverage is possible across lower MI and
   adjacent portions of northeast IN/northwest OH where slightly
   stronger shear supports a more favorable environment for storm
   organization/higher potential for a supercell or two. Given the
   amount of low-level moisture and relatively strong 850mb flow, a
   tornado or two is also possible. As a result, a Slight Risk has been
   introduced across these areas. 

   ...Central/Southern High Plains...
   Far western extent of the front discussed in the synopsis will be
   very defuse at the beginning of the period across portion of the
   southern TX Panhandle. Lee troughing across the High Plains will
   encourage modest moisture return into the southern/central High
   Plains. Additionally, shortwave trough moving through MT and into
   the northern Plains will provide at least modest forcing for ascent
   throughout the High Plains during the late afternoon and evening.
   Good directional shear (0-6km bulk shear around 30-40 kt) and
   moderate instability (i.e. MLCAPE from 2000-2500 J/kg) across the
   southern High Plains will support thunderstorm organization and
   enough severe storm coverage to merit a Slight Risk. More isolated
   severe coverage is anticipated farther north into the central High
   Plains. Large hail will be the primary severe threat for the first
   few hours of development during the late afternoon with the threat
   then transition to strong wind gusts as storms become more linear.

   ..Mosier.. 08/16/2017

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