SPC AC 040600

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Sat Nov 04 2017

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   IL/IN AND NORTHWESTERN OH...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MID MS VALLEY INTO THE OH VALLEY AND LOWER GREAT LAKES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT RISK...

   ...SUMMARY...
   Scattered severe thunderstorms capable of producing large hail,
   damaging winds, and a few tornadoes may occur across parts of the
   Lower Great Lakes, Midwest, and Ohio Valley regions on Sunday.

   ...Synopsis...
   A split flow pattern aloft will continue over much of the
   western/central CONUS on Sunday, with modest 500 mb height falls
   (around 30 dm per 12 hours) forecast to occur across the mid/upper
   MS Valley into the Great Lakes region. A strong southern-stream
   mid/upper-level jet will provide large-scale lift and should
   encourage convective development across parts of the lower Great
   Lakes, OH Valley, and mid MS Valley by Sunday afternoon. An elevated
   mixed layer with steep mid-level lapse rates (around 7-8 C/km in the
   700-500-mb layer) originating from the central/southern Plains will
   overspread these regions through Sunday evening.

   At the surface, a broad and moist warm sector will be in place
   across east TX into the lower MS Valley, extending northward into
   the mid MS Valley, OH Valley, and Lower Great Lakes to the south of
   a warm front. Surface dewpoints reaching into at least the low to
   mid 60s should be common throughout the warm sector Sunday
   afternoon. A weak surface low is forecast to develop northeastward
   along a warm/cold frontal triple point from the vicinity of eastern
   KS/western MO early Sunday to northern IN/southern lower MI by
   Sunday evening. A trailing cold front will progress southeastward
   parts of the mid MS and OH Valleys through the day, likely
   accelerating late in the period.

   ...Lower Great Lakes/Midwest into the OH and Mid MS Valleys...
   Strong effective shear of 40-55 kt associated with the
   southern-stream mid/upper-level jet will likely be present
   along/south of the front mentioned above. Supercell thunderstorms
   may be favored with initial development along the warm front or
   within the open warm sector to the east/northeast of the surface
   low. Given the steep mid-level lapse rates and moist low-level
   airmass that will be present, MLCAPE may increase to around
   1500-2000 J/kg by late Sunday afternoon, even with only modest
   diurnal heating forecast.

   Scattered large hail, some of which may be significant, could occur
   with initial supercell development, particularly across parts of
   central/eastern IL into western/central IN where buoyancy is
   expected to be greatest. The tornado potential should be maximized
   along the warm front through Sunday afternoon as long as the
   convective mode remains at least semi-discrete. Here, low-level
   winds should be backed to a more southerly direction, locally
   enhancing low-level helicity and updraft rotation. Eventual upscale
   growth into one or more bowing line segments may occur from late
   Sunday afternoon into the evening as the cold front begins to
   accelerate southeastward, and the primary severe threat should
   eventually transition to damaging winds. The accelerating cold front
   may tend to undercut ongoing convection by Sunday night, and with
   decreasing instability due to the loss of diurnal heating, the
   overall severe threat should gradually wane with eastward/southward
   extent late in the period.

   00Z GFS/NAM and 12Z ECMWF are in better agreement with the placement
   of the surface warm front Sunday afternoon, which increases
   confidence in the northern extent of appreciable surface-based
   thunderstorm potential and corresponding severe risk. The gradient
   of severe thunderstorm probabilities has therefore been tightened
   across far eastern IA/northern IL and southern/central Lower MI. The
   potential remains for early-day elevated convection across parts of
   IL/IN/OH owing to a strong southwesterly low-level jet. But this
   activity, if it develops, will likely remain isolated and should not
   substantially impact/delay destabilization of the warm sector across
   this region.

   ..Gleason.. 11/04/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z