Mesoscale Discussion 0936
   NWS Storm Prediction Center Norman OK
   0126 PM CDT Sat Jun 12 2021

   Areas affected...portions of northern and central Illinois into far
   west Indiana

   Concerning...Severe potential...Watch unlikely 

   Valid 121826Z - 122100Z

   Probability of Watch Issuance...5 percent

   SUMMARY...A few damaging gusts or a large hailstone may accompany
   the stronger storms this afternoon. A WW issuance is not expected.

   DISCUSSION...Convective initiation has recently transpired across
   far northeast IL per latest KLOT radar data, with visible satellite
   showing deepening CU across northern into central IL in advance of a
   700 mb embedded impulse traversing the synoptic mid-level ridge.
   Weak ascent ahead of the 700 mb impulse along with continued diurnal
   heating/boundary-layer mixing will contribute to a gradual increase
   in convective coverage and intensity through the afternoon.
   Tropospheric winds are weak, with magnitudes below 20 kts in the
   surface-500 mb layer, with only 15-25 kts of effective bulk shear
   present (per 16Z RAP forecast soundings). As such, mainly
   short-lived single cell storms and perhaps transient multicellular
   clusters are expected. 

   90+ F surface temperatures and near 70F dewpoints will support
   widespread 2000+ J/kg MLCAPE and 8-8.5 C/km low-level lapse rates
   given a well-mixed boundary layer in place (already evident via 18Z
   mesoanalysis). A few damaging gusts will be possible with the
   stronger single cell/multicellular clusters. While a 1.0 inch
   diameter stone cannot be ruled out, mainly small hail is expected
   with the freezing level being above 4000 m AGL. 18Z mesoanalysis
   also shows modest 0-3 km vertically oriented vorticity meandering
   across northern IL, where over 175 J/kg 0-3 km is developing. As
   such, a very brief landspout cannot be completely ruled out as well,
   before storms gust out.

   ..Squitieri/Grams.. 06/12/2021

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

   ATTN...WFO...IWX...IND...LOT...ILX...LSX...DVN...

   LAT...LON   40279007 41818890 42238856 42298809 42228787 42038742
               41708718 41048706 40358709 39778741 39478784 39278857
               39378937 39468988 39499020 40279007