875
FXUS63 KLOT 250917
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
317 AM CST Tue Nov 25 2025

.KEY MESSAGES...

- Light rain will transition to drizzle and fog this morning,
  along with the possibility for a period of locally dense fog.

- Very windy (gusts up to 50 mph or stronger) and much colder on
  Wednesday with snow showers and flurries possible for some.

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

- The signal for widespread accumulating snow (and associated
  post-Thanksgiving travel impacts) this weekend continues to
  increase (~70% chance), starting late Friday night, and possibly
  lingering all the way into Sunday morning.

- Below to well below normal temperatures will persist into next
  week, along with the potential for additional rounds of wintry
  precipitation.

&&

.DISCUSSION...
Issued at 305 AM CST Tue Nov 25 2025

Our next wave of rain continues to shift northeastward into
northern IL early this morning in association with the main
approaching mid-level impulse. This area of rain will shift
across the area through daybreak, then likely transition over to
a period of drizzle and fog through most of the morning. The
main concern that we will be monitoring is the threat of dense
fog around and after daybreak this morning. Dense fog has
recently developed across much of southern IA and into northern
MO early this morning, and there is some concern that this area
of dense fog will try to expand eastward into at least western
portions of our area this morning. Confidence on the extent of
any dense fog remains on the lower side, so we will continue to
monitor observational trends this morning.

Regardless of the threat and extent of dense fog, very low
clouds, fog and drizzle will make for a rather "soupy" morning
for the area. While we should see conditions improve some
through this afternoon, lower cloud cover is likely to persist
into tonight. Temperatures today are thus expected to hold
fairly steady, with readings only warming a few degrees into the
low 50s.

Forecast attention then quickly turns to a northern stream
impulse digging into the northern High Plains early this
morning. This feature will strengthen considerably today into
tonight as it digs over the Upper Midwest and ultimately becomes
negatively tilted late tonight over the western Great Lakes. As
this occurs, surface low pressure will rapidly consolidate and
deepen to sub 995 mb near the Straits of Mackinac by early
Wednesday morning. This will send an associated strong eastward
surging cold front across our area this evening.

As has been advertised for the past several days, the main
story with the passage of this front will be the turn towards
very windy and much colder (winter-like) temperatures. This
thinking has not changed, and with the increasing confidence for
strong and frequent gusty winds of 50+ mph, we have opted to go
ahead and hoist a wind advisory for the entire area from late
tonight through Wednesday evening. There is even some concern
that a period of near warning level criteria wind gusts
(damaging winds of 58+ mph) could materialize during the period
of strongest pressure rises (~6 mb/3hr) on the back side of the
deepening surface low Wednesday morning. Currently, it appears
the best chance for such gusts would be across southern WI and
perhaps into portions of far northern IL (north of I-88). We
will have to continue to monitor this potential.

Aside from the strong winds, we should also have a fast
eastward moving line of showers accompanying the frontal passage
this evening. Thereafter, wrap around moisture looks to result
in snow showers and flurries developing into the area on
Wednesday. It appears the best chance for this will be across
far northern IL (north of I-80 and into southern WI), where some
minor accumulations could materialize. Otherwise, expect very
windy conditions through the day on Wednesday, with temperatures
falling into the lower 30s and wind chills into the teens.

KJB



Wednesday Night through Monday:

The main forecast focus is on the increasingly likely (and
possibly long duration as well) widespread accumulating snow
event this weekend. While it`s still too early to start
mentioning specific amounts, there was much better agreement on
the overnight guidance suites in potential for several inches of
snow (ie. a plowable snowfall) for at least portions of the area.
Our biggest impediment to higher confidence is that the
prospective event is still 4+ days out, leaving plenty of time
for sizable changes in how things evolve.

Prior to the (likely) snow onset late Friday night, it will be
primarily dry but cold. This will particularly be the case on
Thanksgiving Day due to still blustery west-northwest winds
frequently gusting up to 35 mph into the early evening. With temps
only topping out in the lower to locally mid 30s after morning
lows in the 20s, wind chills will remain in the teens to around
20F through the afternoon. For any morning outdoor events (such as
community "turkey trots"), wind chills will bottom out around 10F.
Don`t forget to dress for the cold weather.

Later Thursday night into Friday, ~1030 mb surface high pressure
transiting the region will result in much lighter winds, though
temps will be well below normal for the date (teens to low 20s
lows and highs around 30F into the lower 30s).

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 into Saturday across
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. At this time, there is overall
good agreement in the thermal profile and surface wet bulb temps
being cold enough for snow. Some of the more notable question
marks involve the strength of the synoptic system and potential
for some deepening of the surface low into Sunday. The latter
evolution would entail a longer duration of deformation type
precip into Sunday, but also may entail some p-type issues in
parts of the area depending on the track of the surface and 850 mb
low. On the other hand, a weaker and more progressive area of
primarily/solely warm advection type snow would result in an
earlier end time to the accumulating snow (by Saturday evening).

The above is just to give a rough idea of the spectrum of
outcomes, which range from a light to moderate event on some of
the guidance members, to a bonafide snowstorm on a surprisingly
large % of members. Can`t ignore this despite it being far out,
because the above normal column moisture (PWATs possibly over
0.6") 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
already, but much more varied when looking at exceedance
probabilities for higher snow amount thresholds, which is
unsurprising at this range. Finally, a stronger, slower system
would likely result in a couple day quiet but cold period in its
wake, while the faster, weaker system may open the door for
additional snow/wintry precip opportunities into early next week.
Any nights that clear out under surface high pressure could be
quite cold (single digits or colder in spots) if a good snowpack
is established, which remains to be seen.

Castro

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1050 PM CST Mon Nov 24 2025

Forecast concerns include...

Lifr/vlifr cigs/vis with fog/drizzle overnight/Tuesday morning.
Scattered showers through mid morning Tuesday.
Ifr cigs Tuesday afternoon, mvfr cigs Tuesday night.
Very strong/gusty southwest winds late Tuesday night/Wednesday.

A period of showers is expected overnight through mid morning
Tuesday. Outside of these showers, areas of drizzle are
expected, possibly lasting through midday Tuesday. There will be
another chance of showers Tuesday evening ahead of a strong cold
front. Toward the end of the new 30 hour ORD/MDW forecast, near
daybreak Wednesday morning, there is an increasing chance of
snow showers. Opted not to include these as they may be arriving
around 12z, but trends will need to be monitored for later
forecasts.

Ifr cigs have been as far east as DPA/06C this evening, but
continue to remain west of ORD/MDW. Guidance trends continue to
support low mvfr cigs developing in the next few hours for the
Chicago terminals and quickly lowering into ifr and then into
lifr and possibly vlifr for a time around/after daybreak.
Further west including RFD/DPA, lifr/vlifr cigs/vis look on
track. These lowest conditions will occur as a broad weak area
of low pressure moves across the area. As this passes,
visibilities should steadily improve with cigs lifting through
ifr by early afternoon and likely into low mvfr during the
afternoon with mvfr cigs continuing Tuesday evening into early
Wednesday morning.

Light southeast winds are expected to become light and variable
overnight and then shift light westerly by mid/late morning as
the low shifts east. Winds will turn back southwest late Tuesday
afternoon into Tuesday evening with speeds/gusts slowly
increasing. Once the cold front moves through, west/southwest
winds will quickly increase with gusts into the lower/mid 30kt
range. Higher gusts, possibly to 40kts will be possible around
and after daybreak Wednesday morning. cms

&&

.MARINE...
Issued at 317 AM CST Tue Nov 25 2025

A powerful cold front trailing from deepening low pressure
across the Northern Great Lakes will sweep across the lake
tonight. In the wake of the frontal passage, westerly winds
will quickly increase to gale force. The strongest winds, up to
45 kt at times, look to occur during the day on Wednesday, with
occasional storm force gusts even in the realm of possibility.
Lower end gales will then likely persist through the evening
hours on Thanksgiving Day.

The Gale Watch that was in effect has been replaced with a Gale
Warning, in effect from the pre-dawn hours of Wednesday through
Thursday evening across southern Lake Michigan.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory from 3 AM to 9 PM CST Wednesday 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 from 3 AM CST /4 AM EST/ to 9 PM CST /10 PM EST/
     Wednesday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning from 3 AM Wednesday to 10 PM CST Thursday for the
     IL and IN nearshore waters.

&&

$$

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