Mesoscale Discussion 1780
   NWS Storm Prediction Center Norman OK
   0128 PM CST Tue Nov 10 2020

   Areas affected...northern IL and including the greater Chicago
   metro...southeast WI

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

   Valid 101928Z - 102100Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A tornado watch is likely by 3pm CST for northeast IL
   northward into southeast WI.  The forecast primary severe hazards
   are 55-70 mph gusts and a QLCS mesovortex threat capable of
   brief/weak tornadoes and/or narrow swaths of stronger gusts.  The
   supercell tornado threat is conditional and a bit more uncertain. 
   The greatest tornado risk will generally be located north of I-80 to
   the east/southeast of the surface low.

   DISCUSSION...The radar mosaic as of 125pm CST shows a squall line
   from the IA/MO/IL border extending southward into central MO.  A
   stalled surface front largely parallels the IA/IL border extending
   northeast into southeast WI.  Surface temperatures have warmed into
   the lower 70s F with dewpoints around 60 F in the warm sector
   south/east of the boundary.  The 1pm Lincoln, IL special raob showed
   a 10.4 lowest 100 mb mean mixing ratio suggesting limited additional
   increase in low-level moisture is not likely (i.e., dewpoints rising
   into the 62-64 deg range).  Likewise, the 19z Davenport, IA special
   raob showed a similar boundary layer moisture profile---lending
   confidence in this moisture assessment.  

   Both special raobs showed enlarging hodographs and this is occurring
   in observed data at the KMKX and KLOT VADs.  RAP forecast soundings
   for 4pm-7pm across northeast IL and southeast WI show larger CAPE
   (due to the aggressive low-level moisture scenario) than what will
   probably occur.  Given the overall weak CAPE/high shear setup in a
   strongly forced regime, it appears a squall line with an attendant
   damaging wind/severe gust hazard will be the primary risk, along
   with the possibility for a few weak/brief QLCS mesovortex tornadoes.
   The main corridor for severe will probably focus across northern IL
   into southeast WI to the east/southeast of the surface low track
   this afternoon/evening.

   ..Smith/Hart.. 11/10/2020

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

   ATTN...WFO...LOT...ILX...MKX...DVN...

   LAT...LON   42468993 43418895 43788775 43438754 41878731 40578793
               40598859 41518940 42468993