<pre>ACUS11 KWNS 260054 SWOMCD
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
Concerning…Blizzard
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 www.spc.noaa.gov for graphic product…
ATTN…WFO…LOT…ILX…MKX…DVN…
LAT…LON 41349111 42049035 42668896 42768779 42008763 41628760
40978822 40948870 41228944 41369046 41349111 </pre>
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