199
FXUS63 KLOT 092003
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
203 PM CST Tue Dec 9 2025

.KEY MESSAGES...

- A brief period of freezing rain may result in a glaze of ice
  on untreated surfaces this evening, impacting part of the PM
  commute (~5-9 PM CST), mainly northwest of a Rochelle to
  Waukegan line (30% chance).

- Strong southwest winds are expected late this evening before
  becoming northwest on Wednesday (gusts to 35-40 mph).

- The potential for hazardous travel conditions is increasing
  for the Wed AM commute due to a period of wind-whipped snow.

- 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.

- Temperatures will turn colder for the latter half of the week
  and especially this coming weekend, when dangerously cold wind
  chills may also be observed at times.

&&

.DISCUSSION...
Issued at 203 PM CST Tue Dec 9 2025

Through Wednesday:

Two primary concerns are the potential for freezing rain early
this evening across the far north and then a period of moderate
snow or snow squalls Wednesday morning.

Some sunshine earlier today and warmer air on southwesterly
winds allowed temps to warm into the mid 30s for the southern
two thirds of the cwa or so. Low clouds limited sunshine across
the far north where temps are near or slightly below freezing.
With dewpoints slowly rising into the upper 20s/lower 30s, temps
may only fall a few degrees with sunset before rising again
during the evening. The challenging part is how much temps may
drop before or during the precip arrival across the far northern
cwa, which may result in a short duration of freezing rain on
lesser traveled pavement.

The current forecast has just a chance of freezing rain mainly
from a Dixon to McHenry line. Have only tweaked this by
maintaining chance pops for freezing rain, but shifted slightly
south, mainly from a Rochelle to Waukegan line, though overall
confidence is low. There may also be some snow that mixes with
the rain, or freezing rain, this evening, mainly across the far
northern cwa. With the short duration of any possible freezing
rain, will continue with an SPS to highlight the potential. The
precipitation will become all rain by mid evening and then is
expected to taper off after midnight with at least a few hours
overnight with little to no precipitation falling.

Southwest winds will continue to diminish through sunset, then
will steadily increase this evening with gusts into the 30-40
mph range and then shift westerly overnight. While it will
remain windy, the strongest winds appear to have shifted mainly
southwest of the cwa and not planning any wind advisories at
this time.

Much of the 12z guidance shifted from showing mainly snow
squalls Wednesday morning, to now showing a band of snow along
the front that moves across the area. The results may be the
same, a short period of wind blown moderate snow with low
visibility and minor snow accumulations during or toward the end
of the morning rush hour. There is also the potential for some
lake enhancement across far northeast IL. Initially, temps may
be around freezing and marginal for accumulation, but it appears
temps will drop at least into the lower 30s with the snow and
perhaps upper 20s as the cold front moves through and if the
snow is indeed moderate, then some minor snow accumulation, less
than one inch, is possible. Lake effect snow may continue into
Wednesday afternoon across Porter County in northwest IN and
there may be some lingering snow showers and flurries across the
rest of the area. cms

Wednesday Night through Tuesday:

An active belt of strong northwesterly upper-level flow will
persist in tandem with an associated lower-level baroclinic zone
oriented from the northern Plains southeastward across the lower
Great Lakes through later this weekend. Accordingly, the parade of
of clipper-type systems dropping southeastward across our general
region will continue into the weekend, with each one coming with
good chances (50%+) of accumulating snowfall in our very near our
area.

There are currently two distinct periods of potential accumulating
snow we are watching for at least portions of the area Thursday
through the weekend. The first, looks to come with a clipper
Thursday night into at least early Friday, with the second coming
with another clipper on Saturday. Each clipper is likely to lay
down a ~150 mile wide swath of accumulating snow, with an even
narrower corridor of more substantial accumulations (perhaps in
excess of 4"), from the Upper Midwest into the lower Great lakes
region. The main question that remains, is which areas will be
favored for some of the more substantial amounts and rates.
Ultimately, this will be tied to the exact placement of the lower-
level baroclinic zone where the strongest mesoscale frontogenetic
response can be expected to enhance snow rates.

Currently, ensemble guidance is favoring areas southwest of the
Chicago metro area for some of these potential higher snow rates
from the first clipper (Thursday night into early Friday), with
generally lighter amounts in the Chicago area. With that being
said we will have to watch this as there still continues to be
some spread. For the Saturday clipper, there continues to be a
a signal in the guidance that the swath of better accumulations
could be a bit farther to the north, potentially impacting more
of northern IL and northwestern IN. In addition, the Saturday
system in particular may feature notably higher than climo
(~12:1) snow ratios. Nevertheless, while some uncertainty
persists we will need to keep an eye on these two periods for
potential impacts to travel from accumulating snowfall in, or
very near, the area.

Aside from the snow potential, the other weather concern this
weekend continues to be the very cold conditions 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 is the potential
for a period of blustery northwesterly winds to accompany this
deep cold over the weekend and produce subzero wind chills,
potentially as low as -15 to -25 below early Sunday morning.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1138 AM CST Tue Dec 9 2025

Key Messages:

- Strong and increasingly gusty winds expected tonight into
  Wednesday, initially from a southwesterly to westerly
  direction, then turning northwesterly early Wednesday
  morning.

- A period of rain expected this evening.

- About a 1 to 3 hour period of wind-whipped snow showers and
  associated low VSBY`s expected early Wednesday morning.

A potent clipper system will race east-southeastward across
southern WI tonight into early Wednesday morning. This
approaching system will foster increasingly gusty winds
(25-30kt) from the west-southwest tonight, followed by a period
of 30-35 kt west-northwesterly gusts with a cold frontal
passage Wednesday morning. Northwesterly winds are then
expected to remain gusty into the afternoon, but magnitudes will
ease through the day.

A majority of the precipitation with this system is anticipated
to remain north of the the area. With that being said, a period
of rain is still expected for a few hours this evening before
waning overnight. Still cannot rule out a very brief (<1 hour)
wintry mix with the rain onset this early this evening, but the
chances and duration of any wintry mix are expected to remain
short enough to exclude the mention from the main terminals.

Finally, a second period of precipitation is expected with this
system early Wednesday morning (roughly 11 to 15Z timeframe) as
the cold front and colder airmass surges back southward into
the area. Precipitation type with this batch of precipitation is
expected to be snow, with some minor accumulations possible. In
combination with the strong gusty northwest winds, wind-
whipped snow showers may support a short (1-2 hour) period of
sub 1 mile VSBYs early Wednesday morning. Conditions should then
gradually improve mid to late morning as the snow shifts out of
the area, though some MVFR CIGs look to persist into the
afternoon.

KJB

&&

.MARINE...
Issued at 210 PM CST Tue Dec 9 2025

A gale warning remains in effect from late this evening through
Wednesday afternoon. Strong low pressure will move across
southern WI this evening and cross south/central Lake Michigan
early Wednesday morning. Southwest gales are expected to develop
by late this evening, turning westerly overnight then shift to
the north by mid morning Wednesday. The highest speeds, likely
in the 40kt range with perhaps a few higher gusts, are expected
when the winds shift northerly mid morning Wednesday. Speeds
will gradually diminish Wednesday afternoon with gales expected
to end by early Wednesday evening. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning from 9 PM this evening to 3 PM CST Wednesday for
     Winthrop Harbor IL to Gary IN.

     Gale Warning from 9 PM this evening to 6 PM CST Wednesday for
     Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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