005
FXUS63 KLOT 011128
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
528 AM CST Mon Dec 1 2025

.KEY MESSAGES...

- Winter weather advisory for the entire area this afternoon
  into tonight for 2-4 inches, with locally higher amounts south
  of I-80.

- Patchy freezing fog early this morning, mainly west and south
  of the Chicago metro area.

- Well below normal temperatures will persist through this
  weekend with wind chills -5 to -15 possible Thursday and
  Friday mornings.

&&

.DISCUSSION...
Issued at 239 AM CST Mon Dec 1 2025

Patchy freezing fog will be possible early this morning, mainly
west and south of the Chicago metro area. Fog here at LOT has
slowly improved over the past hour and with a rather shallow
moisture layer, expect the fog to remain patchy and variable and
plan to continue SPS mention and will monitor trends through
daybreak.

Winds have shifted southeast across the southeast portion of
Lake Michigan and this has allowed a narrow band of lake effect
snow to develop over the lake and as winds turn southerly
through the morning, this lake effect snow is expected to remain
over the lake and then shift further northeast today and thus,
no mention of light snow or flurries this morning.

Snow is expected to spread and develop across the entire area
this afternoon impacting the afternoon/evening commute. Some
minor changes this morning included increasing snow/water ratios
into the 17:1 range to account for a bit deeper DGZ zone passing
across the area for a 2-4 hour period, which may result in a
period of moderate to perhaps briefly heavy snow. Still some
uncertainty for exactly where the best banding may develop,
which could end up being along/south of I-80. Qpf amounts still
look reasonable in the 0.2 to 0.25 inch range, though perhaps
higher in a narrow band. This would then yield 2 to 4 inches of
snow with locally higher amounts possible, mainly south of I-80
as noted above. A shift further south would then lower amounts
across northern IL and its possible across far northern IL,
amounts may only be in the 1-3 inch range. While amounts remain
on the low end of advisory criteria, at least for the northern
half or so of the cwa, had to make a decision for an advisory or
SPS and given the potential for moderate snow falling during the
rush hour, opted to go with an advisory for the entire area, two
segmented to account for an earlier start in IL and a later end
across northwest IN. Falling snow is expected to end prior to
the Tuesday morning rush hour, but any untreated surfaces may
be slippery or snow covered.

Tuesday is expected to be dry but cold. After morning lows in
the teens for most areas, highs may struggle to reach the mid to
upper 20s. Temps may increase back to around or just above
freezing on Wednesday ahead of a strong cold front. Precip
chances remain uncertain along and ahead of the front and its
possible, maybe likely that precip will develop right over the
cwa during the afternoon. Previous discussion noted the
potential for some freezing drizzle and that is possible along
with a mix. For now, have not made any changes to the blended
guidance which is high chance pops along with all snow for
precip type. Precip would be short in duration and quickly move
east of the area Wednesday evening.

Northwest winds will increase behind the front with gusts into
the mid 20 mph range during the evening, slowly diminishing into
the 10 mph range by Thursday morning. Low temps by this time
will likely be in the single digits for most of the area, with
subzero single digits across the northwest cwa, with wind chills
into the -5 to -15 range. High pressure will move across the cwa
on Thursday as high temps struggle into the lower/mid teens. The
high moves east Thursday evening with southerly winds by Friday
morning but low temps still in the subzero single digit lows for
most areas away from Chicago and wind chills in the -5 to -15
range again.

Quite a bit of uncertainty for the end of the week into the
weekend. There seems to be some consensus for a system moving
across the area, but large differences in timing, strength,
temps, precip types, etc. Blended guidance is now just slight
chance pops for the weekend and made no changes. cms

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 528 AM CST Mon Dec 1 2025

Key Messages:

- Patchy fog/freezing fog west and south of ORD/MDW early this
  morning. DPA/RFD have observed this at times overnight and are
  the most likely to do so early this morning.

- Period of accumulating snow with IFR conditions is expected
  this afternoon/evening.

- IFR/MVFR cigs may linger into Tuesday morning after snow
  departs.

Light/variable or calm winds to start the day in association
with surface high pressure ridge extending from IA eastward
across northern IL/IN. Mainly clear skies earlier in the night
had allowed for the development of patchy freezing fog across
portions of northern IL west/south of Chicago, though increasing
and thickening high cloud cover has largely limited the
coverage of fog. DPA and RFD have had brief intermittent VLIFR
conditions in patchy fog, and can`t rule out some additional
impacts early this morning for these two sites.

Attention then turns to the expectation for a period of
accumulating snowfall expected across the terminals from this
afternoon through this evening. This will likely bring
visibilities down into IFR for several hours, before eventually
tapering off late this evening. Accumulations are expected to be
in the 1-4 inch range. There are indications in current model
guidance that IFR stratus and potentially some fog may linger
late tonight into early Tuesday behind the departing system,
though confidence is somewhat low at this distance.

Aforementioned light/variable winds will become light south-
southwest later this morning and may back slightly south-
southeast this afternoon/evening. Winds will then shift to the
west-northwest tonight, remaining generally under 10 kts.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory from 2 PM this afternoon to midnight
     CST tonight for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-
     ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Winter Weather Advisory from 4 PM CST /5 PM EST/ this
     afternoon to 3 AM CST /4 AM EST/ Tuesday for INZ001-
     INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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