451
FXUS63 KLOT 021141
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
541 AM CST Tue Dec 2 2025

.KEY MESSAGES...

- Areas of freezing fog early this morning.

- Possible (40-60%) period of light snow Wednesday afternoon
  with any snow accumulations less than one inch.

- Well below normal temperatures through the weekend with wind
  chills -10 to -20 expected Thursday and Friday mornings.

&&

.DISCUSSION...
Issued at 216 AM CST Tue Dec 2 2025

Clouds scattered quickly as the snow ended and areas of freezing
fog quickly developed, most concentrated along the I-80 corridor/
Fox Valley in IL, currently. Visibility has improved quite a bit
here at LOT recently as stratus clouds moved back through.
Forecast soundings also suggest low level winds will increase
into the 10-12kt range over the next few hours and this may help
mix the low levels enough to limit any widespread dense fog.
Issued an SPS earlier for the entire area which expires at 10z,
with fog mention in the grids/forecast until 12z. Will take
another look for refinement before sending products this
morning. Another SPS may be needed for at least patchy freezing
fog through mid morning.

Any remaining light snow will end over the next few hours and
plan to let the rest of the winter weather advisory expire at
09z. However, untreated surfaces may still be partially snow
cover and slippery this morning.

A ridge of high pressure will quickly move across the area today
with winds turning southerly by this evening and then gradually
increasing in speed overnight with some gusts into the 20-25 mph
range possible by daybreak Wednesday morning. Low temps will
likely occur this evening, generally in the upper teens and then
temps will level off an begin to slowly rise overnight.

A strong cold front will move across the area Wednesday
afternoon into early Wednesday evening. Precip chances along and
ahead of this front remain uncertain with guidance about equally
split between just some flurries or a brief period of light
snow. Blended guidance pops have jumped to likely for much of
the central cwa Wednesday afternoon. If snow occurs, it will
likely be a high pop, low qpf event and opted to make no
changes. Snow amounts will be light, less than one inch and many
areas may see just a dusting/trace.

The cold air surges into the area Wednesday night on gusty
northwest winds into the mid 20 mph range, which will diminish
to 10 to 15 mph by daybreak Thursday morning. Low temps will
likely be in the subzero single digits across northwest IL and
in the low single digits for the rest of the area, perhaps a
little warmer downwind of Lake Michigan in northwest IN. This
temp/wind combination will likely produce wind chills in the -10
to -15 range for most areas.

High pressure will quickly move across the area Thursday and is
a bit faster in the latest guidance. This allows for some weak
warm air advection by late afternoon and then pretty decent
warming aloft Thursday night into Friday morning. Blended high
temps in the lower/mid teens may be a touch too cold, but made
no changes. However, did warm low temps Thursday night, as they
will tank Thursday evening and then level off and may slowly
warm by daybreak Friday. This still yields subzero single digit
low temps. Even if temps level off and slowly warm overnight,
southerly winds will slowly increase Thursday night into Friday
morning, keeping wind chills in the -10 to -20 range for much of
the area.

There remains quite a bit of uncertainty for a possible system
this weekend and then perhaps another system for early next
week, both of which could produce at least some accumulating
snow for parts of the area. Blended guidance low chance pops
seem fine for now. cms

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 541 AM CST Tue Dec 2 2025

Key Messages:

- Period of LIFR conditions likely early this morning in low
  stratus/fog.

- Confidence remains low on IFR/MVFR ceiling trends today and
  tonight. Also lower confidence in improvement to VFR late
  this evening/overnight as winds turn southwest and become
  breezy.

- Potential for light snow by Wednesday afternoon. Some spread
  in onset time, but have included a PROB30 at the end of the
  ORD/MDW TAFs for this.

Mid-level disturbance is moving east of the area early this
morning, with light snow having ended across the terminals.
Partial clearing overnight has lead to development of IFR/LIFR
and VLIFR stratus and fog upstream across IA/western IL, which
is now spreading eastward across the terminals at TAF issuance
time. Expectation is that there will be a several hour period of
IFR through midday, with a few hour period of LIFR/patchy VLIFR
as the stratus/fog arrives. Several obs of 200-400 foot cigs
across northern IL support this currently. Sub-1SM vis has been
more localized, though there are a few <1/4SM to 3/4SM obs and
can`t rule out brief lower vsbys over the next 1-2 hours.

Model guidance continues to struggle with trends of the shallow
stratus deck later this morning into this evening. Have
maintained a slightly pessimistic stance with IFR cigs lingering
through midday/early afternoon before improvement to MVFR.
Satellite extrapolation of trailing edge of MVFR deck across
central IA would suggest this not clearing out until later
tonight, which is supported by some guidance. Improvement to
VFR appears possible after midnight as southwest flow
strengthens, though lingering low-level moisture could support
continued or redevelopment of low stratus.

Speaking of winds, light westerly flow is anticipated to
eventually turn more southwest late this afternoon/evening.
Speeds then increase late evening/overnight as the gradient
tightens up ahead of a cold front which will move across the
area Wednesday. Gusts in the 20-25 kt range are possible from
after midnight into Wednesday morning.

Light snow is expected to develop ahead of the approaching
front by midday Wednesday. Higher chances appear to be beyond
18Z, but have included a PROB30 at the end of the ORD/MDW
30-hour forecasts.

Ratzer

&&

.CLIMATE...
Issued at 225 PM CST Mon Dec 1 2025

Chicago           Cold High       Low
Thursday 12/4     13 (1991)      0 (1893)
Friday 12/5                      4 (2005)

Rockford          Cold High       Low
Thursday 12/4      7 (1991)     -4 (1991)
Friday 12/5                     -5 (2005)

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from midnight tonight to 9 AM CST
     Thursday for the IL nearshore waters.

     Small Craft Advisory from midnight tonight to 3 PM CST
     Thursday for the IN nearshore waters.

&&

$$

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