Mesoscale Discussion 0163
   NWS Storm Prediction Center Norman OK
   0250 PM CST Tue Feb 27 2024

   Areas affected...Northern IL and far northwest IN

   Concerning...Severe potential...Tornado Watch likely 

   Valid 272050Z - 272245Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A few supercells are expected to develop over parts of
   northwest Illinois and then spread east-northeast across northern
   Illinois into far northwest Indiana through early evening. Very
   large hail to around baseball size will be the primary initial
   threat. A conditional strong tornado scenario may develop later over
   northeast Illinois into far northwest Indiana.

   DISCUSSION...20Z subjective surface analysis placed a 990-mb cyclone
   near the Quad Cities along a pronounced cold front sweeping
   southeast across the Upper MS to Lower MO Valleys. A bent-back plume
   of relatively richer surface dew points from the mid to upper 50s
   lies immediately ahead of this wave, along the northwest periphery
   of the broader warm-moist sector across the OH Valley and lower
   Midwest. Within the exit region of an intense mid-level jet shifting
   east from the southern Great Plains to the Lower OH Valley,
   continued ascent should yield sufficient weakening of MLCIN during
   the 22-23Z time frame. Initial storm development is most likely in
   the immediate vicinity of the surface low.

   The environment will be favorable for discrete supercells forming
   despite initially modest low-level shear. Amid very steep mid-level
   lapse rates, large to very large hail production is expected, with
   peak intensity around 2 to 3.5 inches possible. The primary
   uncertainty is with how convection evolves downstream given the
   relatively narrow warm/moist sector where storms develop. There
   should be a tendency for convection to spread into a drier boundary
   layer towards the WI border. It is plausible, within a scenario
   highlighted by various 12Z MPAS members and occasionally by later
   WoFS/RRFS/HRRR runs, that a longer-tracked supercell or two may
   develop into the broader warm-moist sector across northeast IL into
   far northwest IN. Low-level shear within this region will be
   increasing towards and after dusk, which will conditionally support
   potential for a strong tornado into the EF2-EF3 range (peak
   estimated gusts around 120 to 150 mph).

   ..Grams/Hart.. 02/27/2024

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

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

   LAT...LON   41339107 41889019 42428914 42648804 42478749 41728666
               41188637 40588664 40008714 40078770 40758927 40549065
               41339107