364
FXUS63 KLOT 010839
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
239 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 /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1138 PM CST Sun Nov 30 2025

Key Messages:

- Mist and freezing fog is likely to be observed at RFD and DPA
  through mid-morning.

- A period of accumulating snow with IFR conditions is expected
  tomorrow afternoon and evening.


Winds have become light/calm tonight as surface high pressure
has moved into the region. Despite cirrus streaming overhead and
some lingering VFR stratus over interior northern Illinois,
temperatures have tanked enough for mist/fog to develop near DPA
and RFD. Thus, at least temporary visibility reductions are
likely to occur at both of these sites through the early to
mid-morning hours. Additionally, temperatures in the single
digits and low teens will allow for the fog droplets to freeze
upon contact with various surfaces wherever the fog becomes
dense enough.

The other main forecast item of note for the current TAF cycle
is a period of accumulating snow tomorrow afternoon and
evening. Total snow accumulations with this round of snow are
expected to end up in the 1-4" range at our five TAF sites this
time around, but steady snowfall will still likely knock
visibilities down to IFR levels for several hours and bring
ceilings down to MVFR or IFR levels as well. Winds are expected
to be out of the south or southeast during the snowfall, but
should remain at or under 10 kts for the most part. The snow is
expected to end sometime during the late evening or early
overnight hours, but low ceilings may persist for a while longer
after the snow has ended.

Ogorek

&&

.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...Small Craft Advisory until 3 AM CST early this morning for the
     IL nearshore waters.

     Small Craft Advisory until 7 AM CST this morning for the IN
     nearshore waters.

&&

$$

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