444
FXUS63 KLOT 101739
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1139 AM CST Wed Dec 10 2025

.KEY MESSAGES...

- Strong southwest winds become west and then northwest this
  morning with gusts to 35-40 mph through early afternoon.

- A period of wind-whipped snow may lead to hazardous travel
  during the commute this morning.

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

- Bitterly cold temperatures and potentially dangerously cold
  wind chills are expected this weekend.

&&

.DISCUSSION...
Issued at 330 AM CST Wed Dec 10 2025

Through Thursday:

Quite the difference in model guidance compared to 24 hours ago for
this morning`s snow potential. The earlier concerns of a potentially
robust snow squall tracking across the area have instead trended
toward a broader area of snow with more muted snowfall rates over a
slightly longer duration. This is associated with the trailing
western portion of the elongated mid-level wave/vort, currently
drifting southeast over southeast Minnesota toward the area. In
addition to the snow, winds will remain rather gusty through the
morning as we transition back to a cold advective regime, turning
northwest to 35-40 mph behind the associated cold front. Regardless,
the anticipated impacts for the Wednesday AM commute have remained
largely the same with wind whipped snow and accumulations of up to
0.5-1" leading to hazardous winter driving conditions. Plan on extra
travel time and take it slow on the roads this morning!

Hi-res guidance also continues to suggest a narrow lake effect band
develops toward mid-morning into northeast Illinois that quickly
pivots southeast into northwest Indiana and then east of the area by
mid afternoon. Given the short duration over any given location,
impacts may be more muted, but it could lead to locally higher
totals near the lake of up to 1-1.5", highest in northwest Indiana
near the lake.

Temperatures will steadily fall back below freezing in the wake of
the front through the afternoon from northwest to southeast.
Any lingering wet pavement will have the potential to become slick
as well, particularly on untreated elevated surfaces which will cool
more quickly than the ground. The breezy conditions may help dry
things off somewhat, but recent rains may have also washed off the
residual road treatments as well. Scattered snow showers and
flurries could linger at times through the afternoon and
particularly in the evening. This is associated with a subtle
trailing low-amplitude mid-level wave moving overhead providing some
weak lift within the stratus layer situated within part of the DGZ.
Have held onto 20% chances through this time when an additional
streaky dusting of snow will be possible. Temperatures continue to
drop overnight into the upper single digits toward the WI/IL state
and teens across the rest of the area. Minimum wind wind chills
likely drop into the 0 to 10 degree range.

Our next clipper system will be approaching the area during the day
on Thursday as temperatures warm into the 20s. While some light snow
could begin prior to sunset over portions of northwest Illinois, the
better potential exists for onset during the evening. More details
on that are included in the long term discussion below.

Petr


Thursday Night through Tuesday:

The stubborn northwest flow pattern will persist over much the
CONUS through the latter half of the week and into the upcoming
weekend. With the energetic jet stream and associated baroclinic
zone lining up directly over Illinois and Indiana, the barrage
of clipper-type systems getting sent into the Midwest/Great
Lakes will continue through at least this weekend with
accompanying chances for additional snow accumulations to occur
somewhere in or very near our forecast area.

The first of these late-week clippers is still slated to dive
through the region late Thursday through early Friday, with
Thursday night being the main time frame of concern for
potential snow accumulations in our area. This clipper`s surface
low will track southeastward from South Dakota into the Lower
Midwest with frontogenesis on its eastern flank expected to play
a key role in inducing an elongated snow band within a
northwest-southeast oriented low-/mid-level baroclinic zone. 00Z
global deterministic and ensemble guidance generally depicted
an overall southwestward shift in both the track of the
clipper`s surface low center and the associated QPF/snowfall
footprint. It should be said, though, that there`s still a non-
trivial spread in the track of the surface low across all
global ensemble suites, and this more southwesterly low track is
not yet depicted in some of the higher-resolution guidance
whose time ranges have only recently started to include the late
Thursday/early Friday time frame. Thus, there`s still room for
additional shifts to occur in guidance over the next 24-36
hours.

If this more southwesterly track to the surface low were to
verify, then that would favor any Winter Weather Advisory-worthy
snow accumulations remaining confined to our southwestern
counties, or even to areas farther southwest and primarily
within the DVN and ILX CWAs. Some lesser snow totals would still
be observed farther northeast, but the frontogenetically-driven
nature of the snowfall suggests that there will likely be a
fairly sharp snowfall gradient somewhere -- one that can`t
reasonably be depicted in our forecast grids at this range.
Either way, with surface temperatures expected to fall into the
low-mid 20s and teens Thursday night, even relatively "minor"
snow accumulations could lead to a slick Friday morning commute
for many.

Another shortwave trough embedded within the northwest flow
aloft will track over the Upper Midwest on Friday. A majority of
individual ensemble members favor the accumulating snow
associated with this wave to largely remain to our north.
However, there is still enough support overall for light snow
getting into at least our northern counties to warrant
maintaining some lower-end PoPs (20-40%) as output by the NBM
for the Friday afternoon and evening time frame.

Then, a third shortwave trough is still expected to zip into
the region on Saturday. The EPS, GEFS, and CMCE have all
gradually jogged southward towards central Illinois and Indiana
with this shortwave`s associated QPF footprint over the past 24
hours, but there`s still enough of an overlap with our CWA that
the higher-end chance and lower-end likely PoPs from the NBM for
Saturday still look fine for now. With much colder and drier
air expected to be in place over the region at this time, any
snow that does fall here will likely have a high snow-to-liquid
ratio and, thus, a fluffy (and quite possibly even dust-like)
character to it. One more shortwave trough may dive into the
Great Lakes on Monday before the synoptic flow pattern finally
starts to exhibit some changes, but the latest ensemble
consensus favors its associated precipitation remaining north of
our forecast area at this time.

The other weather concern for the long term portion of our
forecast remains the likelihood of bitterly cold temperatures
this weekend. Successive shots of cold air brought in by the
aforementioned disturbances will likely culminate in single
digit and sub-zero lows and possibly even single digit highs in
many areas over the weekend. Confidence in our overnight/morning
wind magnitudes still isn`t particularly high at this point in
time, but until a Canadian surface high settles over the region
sometime Sunday into Monday, suspect that there`s a good chance
that northwesterly winds will remain high enough for minimum
wind chills to reach (or at least get close to) our -20F
threshold for Cold Weather advisories in some locations on at
least one morning this coming weekend.

Ogorek

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1139 AM CST Wed Dec 10 2025

Snow is coming to quick end from northwest to southeast across
the terminal airspace late this morning. In spite of this, MVFR
stratus remains rather expansive late this morning, and is
currently encompassing the Upper Midwest and western Great
Lakes region. There thus is no near term hope of scattering the
clouds out, so expect MVFR CIGs to persist, possibly even into
the day on Thursday. Otherwise, winds will remain gusty
(25-30kt) from the northwest into this afternoon, but will abate
with sunset late this afternoon.

Another quick shot of light snow and flurries is expected this
evening as an impulse over MN late this morning shifts into our
area. For the latest set of TAFs we have maintained just a
flurry mention with this activity. However, we will have to keep
an eye on the potential for some brief IFR VSBYs with any
heavier pockets of snow that occur this evening, particularly
at KRFD. This activity will end prior to midnight.

KJB

&&

.MARINE...
Issued at 330 AM CST Wed Dec 10 2025

A Gale Warning remains in effect through this afternoon.
Southwest gales become westerly early this morning then turn
northwest after daybreak. The highest speeds, likely around
40kt with perhaps a few higher gusts, are expected when the
winds shift northwesterly later this morning. Speeds will
gradually diminish later this afternoon with gales expected to
end by early evening.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning until 3 PM CST this afternoon for Winthrop Harbor
     IL to Gary IN.

     Gale Warning until 6 PM CST this evening for Gary to Burns
     Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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