487
FXUS63 KLOT 261703
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1103 AM CST Wed Nov 26 2025

.KEY MESSAGES...

- Strong westerly winds (gusts of 50 to 60 mph) and much colder
  temperatures expected today. A period of flurries and showers
  will also occur today, especially north of Interstate 80.

- Blustery and cold weather continues through the evening hours
  on Thanksgiving Day.

- Impactful snow appears increasingly likely for the region this
  weekend. It`s too early for highly specific snowfall amounts
  and locations, but there is a distinct potential for 6"+
  amounts (and higher end travel impacts) in portions of the area.

- Well below normal temperatures will persist into or through
  next week, perhaps with additional chances for snow.

&&

.DISCUSSION...
Issued at 329 AM CST Wed Nov 26 2025

Through Thursday:

Winds have come up quicker than originally thought in the wake
of the strong cold frontal passage early this morning. This
prompted us to move up the start time of the wind advisory just
shortly after midnight. Aside form this, no other changes have
been made to the going headlines.

A robust storm system continues to take shape across the Upper
Midwest into the Upper Great Lakes this morning. Early morning
water vapor imagery illustrates this nicely, with a negatively
tilted trough axis currently surging northeastward into WI along
the southeastern periphery of the strengthening mid-level
circulation center located just southeast of MSP. Strong
dynamics associated with this trough will continue to deepen the
surface low to a stout sub 995 mb central pressure as it
becomes occluded this morning over northeastern WI and far
northern Lake Michigan.

While a significant winter storm will ensue across the Upper
Midwest into the Upper Great Lakes in association with this
system, our main weather story today will be the persistent
strong gusty westerly winds and much colder temperatures. As
noted above, we have already seen a quicker uptick in the winds
early this morning, with some occasional gusts already
exceeding 45 to 50 mph. Unfortunately, this is just the
beginning, as 50 to 55 mph gusts look to become rather common
across the area this morning and persisting this afternoon.
There have been a good amount of upstream observations of 55 mph
wind gusts across IA overnight, and really see no reason why
such wind magnitudes will not materialize throughout all of
northern IL into northwestern IN today.

We have opted to hold with the wind advisory for today, but
with speeds of 50-55 mph (possibly even briefly as high as 60
mph) this will be a higher end wind advisory event. Accordingly,
if the winds overperform even slightly from our current
forecast, portions of northern IL could need to be upgraded to a
High Wind Warning through the daylight hours today. Winds this
strong can still result in minor property damage and lead to
power outages.

Wind gusts will begin to ease a bit this evening into tonight,
so the current 9 pm end time of the wind advisory still looks
good. However, expect blustery conditions to persist tonight
through Thanksgiving Day as west-northwesterly winds continue to
gust to 30 to 35 mph. The combination of the gusty winds and
the much colder temperatures will result in wind chills
remaining in the teens to low 20s.

Aside from the winds, wrap around moisture along the backside
of the Upper Great Lakes low will allow for a period of snow
showers and flurries today, most notably to the north of I-80
and into far northwestern IN. Some minor accumulations may
materialize in these areas from this activity, but amounts will
remain under a half inch and likely relegated to grassy, colder,
or elevated surfaces.

KJB


Thursday Night through Tuesday:

The main forecast focus is on the widespread accumulating snow
event this weekend, centered on Saturday from the early morning
hours through the evening. Despite the snow onset being about
3-days away, there continues to be good ensemble agreement in an
impactful, plowable snowfall for a sizable chunk of our area,
particularly with northward extent. The time left until the
event adds inherent uncertainty common in winter weather
forecasting. Looking at the various ensemble systems, the
largest spread is in the track and strength of the synoptic
system, which will modulate top end amounts and also any
potential for rain (or drizzle) to mix in with the snow across
portions of the area.

Quiet conditions are expected prior to our increasingly likely
impactful snow event. After a blustery start to Thanksgiving
evening, from later Thursday night into Friday, ~1030 mb surface
high pressure transiting the region will result in lighter
west-northwest winds, though temps will be well below normal for
the date (teens to mid 20s lows and highs around 30F into the
lower 30s).

Returning to the weekend main event, big picture wise, a strong
short-wave trough will come ashore on the Pacific NW coast on
Thursday-Thursday night. Then in response to amplifying ridging
into the Gulf of Alaska, this short-wave will dig into the central
and southern Rockies and result in lee surface cyclogenesis over
eastern or southeast Colorado. The surface low will broaden and
become elongated on Saturday from the lower MO Valley to the
lower and mid MS Valley. The details then diverge a bit Saturday
evening into Sunday, serving to at least modulate the event
magnitude (QPF, snow, impacts).

A broad area of strong warm and moist advection will develop over
the central US, with this and upper jet diffluence resulting in
an expansive area of precipitation well ahead of the surface low
path. At this time, there remains overall good agreement in the
thermal profile and surface wet bulb temps being cold enough for
snow from snow onset through early Saturday evening, and much of
this precipitation being from the warm advection regime. Later
Saturday evening and night is the main timeframe with larger
spread in the spectrum of outcomes.

To simplify things a bit, we`re seeing roughly two "camps" in
solutions, between the notably stronger physics based ECMWF and
EPS ensemble, vs. the overall weaker member solutions of the ECMWF
AIFS and EPS-AIFS, GEFS, Canadian (GEPS), and UKMET (MOGREPS-G)
There is better clustering in a surface low track somewhere near
the CWA or just south, but a much larger % of deeper surface low
members in the EPS. The deeper surface low evolution would entail
a longer duration of deformation type (cold conveyor belt) precip
into early to mid Sunday morning (more QPF, and more snowfall for
areas that stay all snow), but also conceptually a higher chance
for warmer air at the surface to possibly result in p-type issues
extending farther north.

On the other hand, the weaker solutions would have predominantly
warm advection snow and deformation focused farther northwest,
cutting down into the QPF and snow amounts somewhat.
Interestingly, the 850 mb temps are pretty uniformly forecast to
remain below 0 Celsius (only a 10-20% chance of 850 mb temps >=0C
reaching the US-24 corridor on the 00z EPS). So another item we`d
likely have to contend with is the trajectory and expanse of the
mid- level dry intrusion (would likely be larger in a stronger
system), which could result in drizzle mixing in with the snow or
a changeover to drizzle. For now, with wet-bulb temps forecast to
remain mostly cold enough for snow, but conceptual support for
some rain mixed in on Saturday night for parts of the area,
indicated a chance of rain over roughly the southeast half or so
of the area. As the surface low tracks into the central Great
Lakes on Sunday, strong cold advection will transition any non-
snow precip back over to light snow, along with gusty northwest
winds. A final note worth mentioning is that periods of onshore
flow with this system may result in milder air from over the lake
cutting down on ratios and amounts some.

The spectrum of outcomes still ranges from a light to moderate
event on some of the guidance members to a bonafide snowstorm on
a surprisingly large % of members, particularly in the ECMWF/EPS
suite, which remains the most robust. Can`t ignore this despite
it being three-days out, because the above normal column moisture
(PWATs likely over 0.6" into central IL) and steep lapse rates
above 500 mb do lend credence to periods of heavier snowfall
rates. The major ensemble systems are basically in unanimous
agreement in 1"+ snowfall in 24-hours (10:1 ratio) already, with
even 50-80% probs for 4"+ amounts, especially near/north of I-80.
The top end potential (6"+) has less overall guidance membership
amongst all the ensemble systems, but with that said, the EPS has
a strikingly large % of members with 6"+ snow amounts (60-90%
near/north of I-80). Ratios where p-type remains snow should
likely be at least 10:1 to perhaps as high as 12-15:1, just to
give a reference on these outputs.

In the wake of the system, the decided trend is towards a couple
day quiet but cold period in its wake. Any nights that fully
clear out under surface high pressure will likely be quite cold
(single digits or even below zero in spots) if a good snowpack is
established, which remains to be seen, but is becoming the more
likely outcome. Finally, we`ll have to keep an eye on any lower
amplitude short-waves for swaths of light snow accumulations next
week amidst an overall well below normal temperature regime. The
first of these timeframes to watch is later Monday through Monday
night.

Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1103 AM CST Wed Nov 26 2025

The main aviation concern through the TAF period is a
continuation of strong north to northwest winds as a low
pressure system moves through the Great Lakes. Gusts of 35 to
45 kt will prevail through the evening before ever-so-gradually
decreasing in magnitude through the remainder of the TAF period.
A few snow flurries/showers will continue throughout the day as
well, before ending overnight. Cigs will remain near or just
above MVFR through the TAF period.

Borchardt

&&

.MARINE...
Issued at 329 AM CST Wed Nov 26 2025

Key Marine Messages include:

- Gale Warning transitioned to a Storm Warning for today for
  for the Illinois and Indiana nearshore waters of Lake
  Michigan. The Gale warning then continues tonight through
  Thursday evening.

- Peak wind gusts of 50 kt Storms today, tapering to 35 to 40
  kt tonight and on Thursday.

Westerly winds will continue to increase this morning, with
speeds likely to top out around 50 KT during the daylight hours
today. While the magnitude of winds will gradually ease tonight
onward, they will remain at or above gale force (35 to 40 kt)
through Thursday evening.

A Storm Warning has been issued for both the Illinois and
Indiana near shore waters for today. This will transition back
to a Gale Warning tonight through Thursday evening.

Borchardt/KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory until 9 PM CST this evening for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
     ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory until 9 PM CST /10 PM EST/ this evening for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Storm Warning until 9 PM CST this evening for the IL and IN
     nearshore waters.

     Gale Warning from 9 PM this evening to 10 PM CST Thursday for
     the IL and IN nearshore waters.

&&

$$

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