Chicago, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

132
FXUS63 KLOT 182357
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
557 PM CST Thu Dec 18 2025

.KEY MESSAGES...

- Scattered wind-whipped snow showers with reduced visibilities
  and rapidly falling temperatures could lead to some slippery
  travel conditions this evening.

- Wind chills of 0 to 10 below expected Friday morning during
  the typical commute hours (~5-9 AM CST). Patchy slick spots on
  untreated surfaces may also linger into the AM commute.

- The blustery and briefly colder conditions tonight into Friday
  will be followed by variable temperatures, but generally
  above normal, into next week.

&&

.DISCUSSION...
Issued at 301 PM CST Thu Dec 18 2025

Through Friday Night:

The main forecast focus and concern is wind-whipped snow showers
and flurries paired with plummeting temperatures this evening
and overnight. This may set the stage for at least patchy slick
spots on some roads as lingering moisture freezes.

Concerns have eased with strong winds with the low topped
strongly forced line of convection out ahead of the cold front,
near/east of I-65 as of this writing. Stratiform rain in the
wake of the cold fro-pa will lag by about an hour or two before
ending. This will be followed by a short lull of 1-3 hours
before snow shower potential ramps up this evening.

Aside from the rain and embedded strong wind trends, the
magnitude of pre-frontal southerly winds has eased just a bit
over northwest Indiana, vs. what was experienced prior to fro-pa
over northern IL.

Westerly winds gusting up to 30-35 mph behind the initial cold
front will very briefly subside (ie. only 5-10 mph winds in RFD
area this hour). Winds will quickly increase again from the
west-northwest as the secondary cold front pushing across the
MS River at this time sweeps across the area through the
evening. Based off upstream observations across eastern Iowa,
expect frequent 35-40 mph gusts through tonight, with
sporadic/occasional gusts around 45 mph.

The cold advection behind the secondary front will be quite
potent (teens into far northern and northwest IA already), owing
to a pocket of nearly -20C air at 850 mb pinwheeling in with the
core of the 500 mb short-wave over the upper MS Valley. Item of
concern here is that the plummeting temperatures will be paired
with scattered snow showers and flurries. Forecast soundings
don`t look classic for snow squalls, but with steep lapse rates
and lift through the DGZ, expectations haven`t changed much
despite the paltry deterministic output.

Relying on upstream radar trends and observations, largely
continued with the idea of mid-high chance range (40-50%) PoPs
peeling southeast with time through this evening and overnight.
It`s possible that the trajectory of more robust snow showers
over central IA focuses them largely south of I-80. However, all
in all, don`t want to rule out the possibility of narrow west-
northwest to east-southeast oriented bands of snow showers
taking shape farther north.

With the above thinking in mind, there may be patchy coatings of
snow and brief sharply reduced visibility underneath any heavier
snow showers amidst general light snow showers and flurries.
With temps falling through the teens and prior rain possibly
washing away some of the road pre-treatments, we`ll continue to
message the potential for localized slick spots developing on
some roads and other paved surfaces. There looks to be enough of
a lag with the stronger cold advection and end of steady rain
this afternoon to preclude a true flash freeze scenario, though
the evening shift will be closely monitoring trends.

Once the snow showers/flurries end for most of the area, there
could be a short-window of lake effect snow showers into
northeast Porter County before that axis shifts east. The bigger
story will be the return to very cold wind chills for the
morning commute. With blustery west-northwest winds only slowly
easing and temperatures in the 10-15F range (localized upper
single digits possible), expect wind chills of around 0 to 10
below. Be sure to dress for the weather if you`ll be spending
time outdoors.

Stratus with some flurries (cloud layer in the DGZ) trapped
under a strong subsidence inversion late tonight may linger
into Friday morning, but substantial low-level dry air advection
should erode clouds from west to east as a surface ridge
crosses the area Friday afternoon. Expect a much colder day on
Friday with highs in the lower to mid 20s. Winds will briefly
diminish to 10-15 mph or less during the mid-late afternoon and
early evening until the next ramp up in winds Friday night. As a
result, only a small drop in temperatures is expected Friday
evening as a 50 knot LLJ spreads over the area and results in
steady WAA through the night.

Castro/Kluber

Saturday through Thursday (Christmas Day):

A low-amplitude wave will then cross far western Ontario on
Saturday. A brief warmup into the 40s is expected early in the
day before temps fall with the passage of a cold front during
the afternoon. Marginal moisture profiles may support a narrow
band of light mixed precip along and slightly behind the front
mainly north of I-80 (kept PoPs under 15% due to modeled very
dry sub-cloud layer). Colder conditions with highs in the mid
20s to around 30F and mostly sunny skies will follow on Sunday
as another high pressure crosses the region.

Moisture return ahead of the next storm system passing well to
the north Monday into Tuesday appears to be insufficient for
widespread precip over the area before a weak cold front passes
on Tuesday. Guidance continues to favor the development of a
broad ridge across the central CONUS by early Christmas.
Expansive WAA with steady low-level moisture advection is
expected across the mid-Mississippi River Valley by Christmas
Eve, with a likely area of stratus and drizzle/light rain in the
region. Placement is still a bit far out to pin point, but a
somewhat damp Christmas Eve into Christmas is possible for
parts of the area. What is of higher confidence is the very mild
temperatures, particularly on Christmas Day when highs may push
60F (!) in spots, especially south of I-80.

Kluber/Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 557 PM CST Thu Dec 18 2025

Key Aviation Messages for the current TAF period:

- Gusty west winds through tomorrow morning, with prevailing
  gusts 30 to 35 knots with occasional gusts to 40 knots
  overnight

- Chance for snow showers late this evening which may drop vis
  down to IFR levels

- MVFR cigs tomorrow morning before VFR returns midday as winds
  finally subside

Rain has exited to the east, but the next cold front is
currently in eastern Iowa and crossing the river into northern
Illinois. There is a brief break in the wind gusts with VFR
conditions for Chicago terminals. However, KRFD has been gusting
to 38 knots at the time this discussion was sent. As the front
moves through tonight, MVFR cigs are expected to return,
westerly wind gusts will increase, and there will be a chance
for snow showers as the front passes through. Given the
character of the snow being showers, it is possible that some
terminals in the area with MVFR cigs and no snow, while other
terminals have a shower passing right over them reducing
visibility down to IFR conditions and accumulating a couple
tenths of an inch. For now, no changes were made to the TEMPO as
it matches a combination of model guidance and trends being
monitored in Iowa.

Westerly winds will remain gusty through tomorrow morning. MVFR
cigs will likely stick around through the morning, but lower
confidence on the exact timing of clearing to VFR (though higher
confidence in VFR in the afternoon). Winds will remain around
10 knots through the day and slowly become more southerly after
00Z. As a stout low level jet ramps up Friday night, there is
the potential for LLWS to be added to the TAFs, but for now
remains outside the current TAF window.

DK

&&

.MARINE...
Issued at 300 PM CST Thu Dec 18 2025

A secondary cold front will move across the southern portions
of Lake Michigan this evening. Westerly winds of 35 to at times
40 kt are expected, and a Gale Warning remains in effect to
cover this. The Gale Warning was extended into/through Friday
morning due to the most recent guidance taking a bit longer to
ease the gale force speeds/gusts. Winds will diminish through
late Friday afternoon as an area of high pressure briefly builds
across the southern portion of Lake Michigan. Gusty southerly
winds will quickly redevelop Friday night ahead of the next cold
front, which will move across the region on Saturday.

Castro/Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Warning until 9 AM CST Friday for Winthrop Harbor IL to
     Gary IN.

     Gale Warning until noon CST Friday for Gary to Burns Harbor IN-
     Burns Harbor to Michigan City IN.

&&

$$

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