469
FXUS63 KLOT 081723
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1123 AM CST Mon Dec 8 2025

.KEY MESSAGES...

- Very low chance (<20%) for freezing drizzle north of I-88 late
  tonight into early Tuesday morning.

- A period of blustery winds and rain followed by snow showers
  is likely Tuesday night into Wednesday.

- After a brief warm-up Tuesday through early Wednesday,
  temperatures will turn sharply colder during the latter half
  of the week and into the weekend.

&&

.DISCUSSION...
Issued at 353 AM CST Mon Dec 8 2025

Through Tuesday:

While lingering lake effect clouds have slowed cooling over
portions of the metro and areas north of I-88, it will be a
chilly start to the work week with temperatures early this
morning in the single digits outside of the Chicago metro,
teens in the suburbs, and upper teens to mid 20s in Chicago
(warmest along the lake front).

A weak mid-level disturbance currently moving through Iowa will
continue its eastward progress into Illinois this morning.
While this feature has been producing some (mainly light) snow
over central Iowa it will be encountering increasingly dry low
to mid-level air amidst an expansive surface high. Nevertheless,
the lighter echoes out ahead of the main band could still lead
to isolated seeder-feeder generated flurries near and west of
I-39 early this morning (~20% chance). Admittedly guidance has
not been handling this feature all that well and it has remained
rather persistent. While the dry conditions are still expected
today, a slower erosion of the lower-level clouds here locally
could perhaps support an additional brief bout of flurries in
the afternoon.

As the center of the surface high shifts to the east through
the day winds will return to a southerly direction. The warm
advective influence will still be less pronounced initially,
with the residual snow pack and mostly cloudy skies holding
high temperatures in the low to mid 20s.

The next clipper system will approach the region tonight and
move across Wisconsin into early Tuesday morning. This will
help further increase the low level warm and moist advection out
ahead of it here locally. Any precipitation associated with
this system looks to remain mainly north of the local area,
though some light wintry precipitation/flurries could graze far
northern/northeast Illinois overnight into early Tuesday
morning. The main concern during this time is whether freezing
drizzle could develop instead of flurries. However, there
remains notable variability among guidance as to whether we
saturate sufficiently this far south for precipitation to occur.
This will be monitored closely for possible addition to the
official forecast if confidence increases as temperatures will
still be below freezing during this timeframe and breezy winds
would be supportive of more efficient ice accretion. Stay tuned.

Temperatures then warm above freezing by late morning/early
afternoon with the possibility for lingering low clouds and
patchy fog/mist making for a dreary day overall. Precipitation
with yet another (likely stronger) system looks to mainly hold
off until after sunset Tuesday. More details on that are
included in the discussion below.

Petr


Tuesday night through Sunday:

The stubborn northwest flow pattern will persist over the
western 2/3rds of the CONUS through this week and into the
upcoming weekend. The energetic jet stream in place over the
country will thus continue to send a barrage of clipper-type
systems into the Midwest over the next several days, resulting
in regular opportunities for (mostly wintry) precipitation and
mostly below normal temperatures during this time frame.

What will likely be the strongest of this series of systems
will pass through the region Tuesday night into Wednesday.
Ensemble guidance is in relatively good agreement on a sub-990
mb surface low swinging across central or southern Wisconsin,
though a minority of individual ensemble members have this
surface low taking a track that brings it just south of the
Illinois-Wisconsin state line. Robust warm air advection ahead
of this deepening system will have pushed temperatures above the
freezing mark during the daytime on Tuesday, and southwesterly
surface winds strengthening further after sunset will keep
temperatures propped up in the mid 30s to possibly even the low
40s through the night as the system`s precipitation spreads into
the area. Thus, while snowflakes could still be seen in some of
our northern locales, the majority of precipitation that we`ll
see Tuesday night should come in the form of a cold rain.

Just how strong winds will get Tuesday night is still something
that will need to be ironed out over the next couple of
forecast cycles. Some guidance favors gusts exceeding 40 mph
during this time frame when low-level pressure gradients will be
most compressed, while other guidance is much more reserved,
believing that precipitation and the deep snowpack in place over
much of the area will stunt mixing into the stronger flow
aloft. The precise strength and track of the surface low will
also play a role in the magnitude of the winds that we`ll see
Tuesday night. For now, the NBM-delivered peak 25-30 kt gusts
appear to be a good compromise between everything, but
modifications to these gusts may need to be made as the event
draws closer.

As the low pressure system makes it east of our longitude,
cooler temperatures will work their way into the area on
Wednesday behind a cold front. Precipitation on the backside of
the low will thus be expected to change over to snow, though
just how widespread the snow will be is another point of
uncertainty with our forecast that is tied to the precise
strength and track of the surface low, among other things.
Regardless, any locations where gusty snow showers materialize
will see sharply reduced visibilities and will have a chance to
pick up a coating of snow if diminishing column moisture doesn`t
end up being too big of a negating factor.

Between Thursday and Sunday, 2-3 additional upper-level
disturbances will ride the northwesterly flow train into the
region. Each disturbance will come with a chance of producing
additional snow accumulations here or somewhere nearby. However,
there still isn`t much consistency in ensemble guidance in the
exact tracks, timing, and strength of each of these disturbances,
which leads to continued low confidence in the finer-scale
details of our precipitation forecast for the end of this week
and this upcoming weekend.

Confidence is much higher that temperatures will turn sharply
colder for the latter half of the week and into the weekend. The
ensemble signal for single digit lows remains quite strong for
this late week/weekend time frame, and there is a good amount of
support for a sizable chunk of our forecast area seeing sub-zero
low temperatures too. A period of blustery northwesterly winds
behind an arctic cold front appears probable as well, which may
allow wind chills to make a run at -20F at some point this
coming weekend.

Ogorek

&&

.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.

     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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