SPC AC 241230

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0630 AM CST Fri Feb 24 2017

   Valid 241300Z - 251200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN
   LOWER MICHIGAN ACROSS EASTERN INDIANA AND WESTERN OHIO TO NORTH
   CENTRAL KENTUCKY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK AREA...FROM LOWER MICHIGAN TO EASTERN TENNESSEE...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK AREA...FROM THE GREAT LAKES TO PARTS OF THE SOUTHERN
   APPALACHIANS...

   ...SUMMARY...
   Severe thunderstorms are forecast to affect areas from Lower
   Michigan southward to Tennessee, mainly this afternoon through
   tonight.  The primary threat appears to be damaging wind, but some
   hail and a couple of tornadoes will also be possible.

   ...Lower MI to TN through tonight...
   A well-defined midlevel trough over the mid MO Valley this morning
   will amplify while progressing eastward to the Great Lakes and OH
   Valley tonight, as an associated surface cyclone deepens while
   moving northeastward from west central IL across Lower MI to Lake
   Huron.  Ongoing elevated thunderstorms will persist through the
   morning across Lower MI in the zone of strong low-level warm
   advection/frontogenesis immediately north of the eventual cyclone
   track, with marginally severe hail possible in the strongest storms.

   Modest low-level moisture (boundary layer dewpoints in the mid-upper
   50s) will spread northward into southern Lower MI beneath an
   elevated mixed layer, though the cap will likely delay surface-based
   thunderstorm development until 21-00z.  Initial storm development is
   likely close to the surface cyclone in southern Lower MI, along the
   northwest edge of the modestly unstable warm sector (MLCAPE near
   1000 J/kg).  Deep-layer vertical shear (effective bulk shear of
   40-50 kt) will favor semi-discrete supercells with an associated
   large hail/damaging wind risk into this evening across southern
   Lower MI.  A couple of tornadoes will also be possible as any
   sustained supercells can interact with the zone of stronger
   low-level shear (effective SRH 200-300 m2/s2) and sufficient
   moisture along the surface warm front.

   Convection will develop southward through the evening as large-scale
   forcing for ascent/height falls overspread the surface cold
   front/west part of the warm sector and erode the cap associated with
   the steep (8-9 C/km) midlevel lapse rates.  A mixed convective mode
   of semi-discrete cells and line segments is expected initially along
   and just ahead of the cold front, given somewhat boundary-parallel,
   deep-layer shear vectors and ascent focused along the front.  Modest
   low-level moisture/buoyancy, lingering steep midlevel lapse rates,
   and 40-50 kt effective bulk shear will support organized line
   segments and supercells capable of producing damaging winds/isolated
   large hail.  The tornado risk well south into the warm sector is a
   bit more uncertain given relatively straight hodographs and a
   tendency toward more linear convection with time.  However, there
   will still be some risk for embedded circulations in the solidifying
   line of storms which will also be capable of producing damaging
   gusts well into the overnight hours.

   ..Thompson/Kerr.. 02/24/2017

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