Storm Prediction Center Mesoscale Discussion 799

   Mesoscale Discussion 0799
   NWS Storm Prediction Center Norman OK
   0736 PM CDT Thu May 15 2025

   Areas affected...Parts of northeastern into central Illinois

   Concerning...Tornado Watch 255...

   Valid 160036Z - 160130Z

   The severe weather threat for Tornado Watch 255 continues.

   SUMMARY...Severe hail and damaging winds are the primary concern,
   though the tornado risk could increase with any sustained supercells
   over the next couple hours.

   DISCUSSION...Severe storms are tracking eastward along the
   north/south-oriented dryline feature across northeastern/central IL.
   Storms have increased in intensity/coverage over central IL (along
   the southern portion of the line), where large-scale ascent in the
   exit region of a midlevel jet is maximized amid strong buoyancy
   (around 3000 J/kg MLCAPE) and minimal inhibition. Given the strong
   buoyancy and 60 kt of 0-6km shear oriented perpendicular to the
   line, these storms will continue to pose a risk of severe hail and
   damaging winds. Sufficient low-level shear (around 30-kt 0-1km per
   ILX VWP) and rich boundary-layer moisture will also support a
   tornado risk, especially with any established supercell structures. 

   Farther north into northeastern IL, storm coverage has been limited
   owing to weaker large-scale ascent. However, as the dryline feature
   intercepts the old lake breeze boundary, an uptick in severe
   potential will be possible over the next hour or two. Ample
   buoyancy/low-level moisture and sufficient low/deep-layer shear will
   support supercell structures capable of damaging winds, large hail,
   and a tornado or two.

   ..Weinman.. 05/16/2025

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LOT...ILX...LSX...

   LAT...LON   42028774 41548755 40548769 39478828 39088878 39118926
               39278962 40038923 40858875 41668878 42288865 42408828
               42318790 42028774 

   MOST PROBABLE PEAK TORNADO INTENSITY...120-150 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN