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Mesoscale Discussion 1664
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   Mesoscale Discussion 1664
   NWS Storm Prediction Center Norman OK
   0654 PM CST Sun Nov 25 2018

   Areas affected...Northern IL and adjacent portions of Eastern
   IA/Southern WI


   Valid 260054Z - 260700Z

   SUMMARY...Heavy snow will spread into a larger portion of northern
   IL this evening. As stronger winds move in from the west, blizzard
   conditions will expand later tonight across the region.

   DISCUSSION...00Z surface analysis depicts a 993 mb surface cyclone
   just northeast of St. Louis. To the north and northwest of the low,
   heavy snow is ongoing from northeast MO into northwest IL, with
   stronger winds in the northwestern quadrant of the cyclone producing
   blizzard conditions. Dual pol products from KILX/KLOT and recent
   surface obs and mPing reports indicate that the rain/snow line is
   moving eastward across northern IL, and this trend is expected to
   continue as backing surface winds result in increasing low-level
   cold advection to the north and northwest of the east-northeastward
   moving surface low. Snow should continue spreading into most of the
   Chicagoland area between now and 02Z, though areas in the immediate
   vicinity of Lake Michigan may see a longer period of mixed
   precipitation as northeasterly winds off of the lake maintain a
   slightly warmer near-surface layer. 

   Substantial convection has been noted near the surface low moving
   into southern IL, with a convective character to the precip (and
   some thundersnow reports) also noted within cooling cloud tops
   across northern IL. Strong low/midlevel frontogenesis will continue
   to favor moderate-to-heavy snow to the north of the midlevel low,
   with some convective enhancement possible just north of the midlevel
   dry slot, where relatively steep lapse rates (in excess of 7 C/km as
   noted on ILX/DVN 00Z soundings) will be maintained. Snow rates of
   1-3 inches per hour are expected within the primary snow band, which
   should shift gradually eastward into northeast IL by late tonight. 

   Strong winds (gusts in excess of 40 kt) are resulting in ongoing
   blizzard conditions from northeast MO into northwest IL. These
   stronger winds will expand eastward with time tonight in conjunction
   with the movement of the surface low, resulting in an expansion of
   blizzard conditions into northeast IL and perhaps far southeast WI
   after 03Z tonight.

   ..Dean.. 11/26/2018

   ...Please see for graphic product...


   LAT...LON   41349111 42049035 42668896 42768779 42008763 41628760
               40978822 40948870 41228944 41369046 41349111 

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