SPC MD 1664


MD 1664 Image

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


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

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