SPC AC 150726

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0226 AM CDT Fri May 15 2020

   Valid 171200Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON
   AND EVENING ACROSS PARTS OF THE OHIO VALLEY INTO SOUTHERN PORTIONS
   OF THE GREAT LAKES REGION...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Ohio Valley into
   southern portions of the Great Lakes region Sunday, accompanied by
   at least some risk for severe weather.

   ...Synopsis...
   An initially broad and deep mid-level low, off the Pacific coast at
   12Z Sunday, appears likely to continue to slowly approach the coast
   Sunday through Sunday night, as a significant short wave
   perturbation digs around its western through southern periphery.  As
   this occurs, downstream ridging is forecast to build across much of
   the Plains.  While the ensemble output of the various models exhibit
   consensus concerning this evolution, developments within branching
   flow to the east are more uncertain.

   In general, a significant wave within one branch is forecast to dig
   from the Upper Midwest into portions of the Great Lakes and Ohio
   Valley region.  It appears that this may be accompanied by a modest
   surface low, along a stalled frontal zone across the southern Great
   Lakes region, and a southward surging cold front in its wake,
   through much of the lower Ohio Valley, Ozark Plateau and central
   Plains by 12Z Monday.  

   Across the southern Plains into northwestern Gulf coastal areas, the
   front will be preceded by another intrusion of cool air, in the wake
   of a short wave trough digging within a weaker branch of westerlies,
   across eastern Texas into upper Texas and Louisiana coastal areas. 
   At the same time, a possible developing tropical cyclone over the
   southwestern Atlantic may gradually merge into this weaker branch,
   downstream, probably well offshore of Carolina coastal areas.

   ...Ohio Valley/southern Great Lakes...
   Lapse rates within the warm sector of the surface low appear likely
   to be relatively weak, and considerable cloud cover could limit
   insolation Sunday.  However, models suggest that mid/upper 60s
   surface dew points may still contribute to CAPE in excess of 1000
   J/kg.  Coupled with moderate shear beneath 30-40+ kt southwesterly
   to westerly flow in the 850-500 mb layer, this may contribute to an
   environment at least marginally conducive to organized thunderstorm
   development, accompanied by a risk for potentially damaging wind
   gusts and some hail.

   ..Kerr.. 05/15/2020

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