746
FXUS63 KLOT 081945
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
145 PM CST Mon Dec 8 2025

.KEY MESSAGES...

- Chance (30%) of light snow along/north of I-80 tonight with a
  dusting of snow accumulation possible. Very low chance (<20%)
  for freezing drizzle late tonight into Tuesday morning, also
  along/north of I-80.

- Period of light freezing rain late Tuesday afternoon into
  early Tuesday evening, mainly northwest of an Ottawa to Joliet
  to Chicago line, during the evening rush hour.

- Possible snow squalls Wednesday morning.

- Windy conditions Tuesday night into Wednesday with wind gusts
  to 40 mph possible.

- More fast moving clipper systems could result in some additional
  periods of accumulating snow in our near our area late this week
  into the weekend.

- After a brief warm-up midweek, temperatures will turn sharply
  colder during the latter half of the week. The deep cold may
  also result in some periods of dangerous wind chills to -20
  this weekend.

&&

.DISCUSSION...
Issued at 145 PM CST Mon Dec 8 2025

Through Wednesday:

There are multiple forecast concerns/challenges through
Wednesday afternoon. The local area will be on the far southern
end of a clipper system moving across the northern Great Lakes
tonight with a chance of light snow overnight, mainly north of
I-80. There may be a dusting of snow accumulation, especially
closer to the IL/WI state line. There has also been the concern
for some patchy freezing drizzle as this light snow potential
ends in the predawn hours, which then could persist through
daybreak. The moisture depth looks rather shallow for freezing
drizzle and confidence remains too low to include in the
forecast but trends will need to be monitored. The gradient
will also tighten tonight with southwest winds gusting into the
middle 20 mph range, which will diminish some on Tuesday.

The next fast moving system arrives late Tuesday afternoon with
some large changes to the forecast. Given how cold the ground
and snow pack is, there remains quite a bit of uncertainty for
how warm temps will rise on Tuesday and if they may cool as
precipitation arrives late in the afternoon/early evening. As a
result, still have high temps generally in the mid 30s Tuesday,
but then have temps falling back into the lower 30s for a large
area northwest of an Ottawa/Joliet/Chicago line. While not a
classic freezing rain set-up, even if the bulk of the
precipitation falling is in the form of liquid rain, less
traveled surfaces, such as sidewalks, parking lots, etc, may
still develop some icing and have included freezing rain in the
forecast for these areas. Both from a precipitation duration and
from a temperature perspective, this freezing rain potential may
only last a few hours. For the rest of the area, air temps
slightly above freezing, should limit freezing rain and have
continued with just liquid rain in the forecast. And since this
is a large change to forecast, plan to hold off on an advisory
to allow trends to confirm these changes as well as where the
cutoff to any possible advisory may be needed.

Also of concern is any further shift south to the track of this
system, which may possibly push the freezing rain potential a
bit further south, but may also bring more snow to far northern
IL. From this distance, confidence is too low to say where the
southern edge of the swath or snow will fall as just a small
change to the track of the system could have large changes to
the precipitation forecast.

As this system approaches Tuesday evening, southwest winds will
steadily increase and then turn more westerly early Wednesday
morning. Wind gusts during this time period may reach 40 mph,
possibly higher, which then could lead for the need for a
possible wind advisory.

By Wednesday morning, the true cold front will moving across the
area and this looks like a good setup for possible snow squalls,
which the HRRR and Namnest are showing well, with locally higher
wind gusts and significantly reduced visibilities. The overall
trend in the models is colder and faster and while there is
still a chance of rain Wednesday morning across the southeast
cwa, its possible that precipitation ends late Tuesday night,
early Wednesday morning and then there are snow squalls in the
morning with lingering flurries snow showers in the afternoon.
With these trends in mind, have lowered temps a few degrees
both Tuesday night and on Wednesday. Northwest winds will remain
gusty Wednesday afternoon, but should be slowly diminishing.

The northwest winds will then likely keep lake effect snow
showers going across at least Porter County in northwest IN
Wednesday afternoon, with some minor snow accumulation
possible. cms

Wednesday Night through Monday:

An active belt of strong northwesterly upper-level flow is
anticipated to persist from the northern Plains southeastward
across the lower Great Lakes through much of the period. This
will steer at least 2 to 3 additional clipper type impulses
southeastward across our general region Thursday and into the
weekend, with each one coming with chances of accumulating
snowfall in our very near our area. With that being said, there
still continues to be little consistency in ensemble guidance
regarding the exact tracks, timing, and strength of each of
these weather impulses. Accordingly, while the chance of more
snow near the area remains elevated (above 50%), confidence
remains low with the finer-scale details of the forecast (such
as the exact timing and which exact areas are the most favored)
later this week through the weekend.

Confidence remains high that temperatures will turn sharply
colder for the weekend as another arctic airmass engulfs much of
the Midwest and Great Lakes region. The ensemble signal for
this remains strong, and current indications continue to
generally support upper single digit to teens high temperatures
and overnight lows at or below zero in most locations for the
weekend. Most concerning at this point is the potential for a
period of blustery northwesterly winds to accompany this deep
cold over the weekend, which could result in some periods of
dangerous wind chills nearing -20F.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1123 AM CST Mon Dec 8 2025

Key Messages:

- Lower MVFR to IFR CIGS likely to develop overnight and
  persist on Tuesday.

- A 30% chance of light snow showers for a couple hour period
  overnight, followed by a possible period of -FZDZ (5-15%
  chance) into early Tuesday morning.

Prevailing VFR conditions are anticipated through the day light
hours today. Winds will generally be light from the south-
southeast.

Tonight, a weather system passing well north of the area will
lead to a wind shift to the southwest late tonight and through
the day on Tuesday. A period of gustiness up around 20 kt may
also accompany this wind shift. The bulk of the precipitation
associated with this system is expected to largely remain north
of the area. However, there is about a 2 to 4 hour window
tonight in which some light snow showers and flurries could
occur over the terminals. Since the chance for this is around
30%, we opted to include a few hour PROB30 mention tonight in
the latest set of TAFs. The possibility also exists for the snow
showers to transition to a short period of -FZDZ very late
tonight into early Tuesday morning. In spite of this, the
chance for this is far too low to include in the TAFs at this
time. Otherwise, expect CIGs to lower into the lower MVFR
category overnight, and could even approach IFR conditions very
late tonight into Tuesday.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 9 PM this evening to noon CST
     Tuesday for Winthrop Harbor IL to Gary IN.

     Gale Watch from Tuesday evening through Wednesday afternoon
     for the IL and IN nearshore waters.

     Small Craft Advisory from 9 PM this evening to 3 PM CST
     Tuesday for Gary to Burns Harbor IN-Burns Harbor to
     Michigan City IN.

&&

$$

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