407
FXUS63 KLOT 040922
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
322 AM CST Thu Dec 4 2025

.KEY MESSAGES...

- Brief period of very cold weather through tonight.

- Series of clippers to bring periodic light snow chances to
  the region through the period. Confidence is not particularly
  high with tracks/timing of these features.

&&

.DISCUSSION...
Issued at 322 AM CST Thu Dec 4 2025

Arctic high pressure (1035mb at Yankton SD at midnight) is
building east-southeast across the Corn Belt early this morning,
in the wake of the sharp cold front which pushed through the
area Wednesday afternoon/evening. Temperatures continue to
steadily fall as northwest winds on the eastern periphery of the
high provide persistent low-level cold advection. Temperatures
are expected to dip into the negative single digits in spots
west of Chicago through/shortly after sunrise and the positive
single digits and low teens farther east. Coldest wind chills
are still expected to be around -15F early this morning, as
temps continue to fall but winds gradually diminish. The surface
ridge is progged to drift east across the forecast area this
afternoon under mostly sunny skies, further reducing wind
speeds. With a substantial early-season snow pack and shallow
mixing, temps will be slow to recover from this morning`s lows,
though sunshine should help. Guidance depicts a large range in
forecast highs for today, from the low-mid teens to the low-
mid-20s for afternoon highs for afternoon highs, and have
blended this to be a little warmer than our previous forecast.

With the surface ridge across the area early this evening,
we`ll see a quick drop in temps after sunset given the light
winds, mainly clear skies and the snow pack. Will likely see
readings drop into the negative single digits in places during
the evening, then become steady/slowly rise overnight as warm
advection develops (especially aloft) as winds turn south and
increase on the back side of the now-departing surface ridge.
Wind chills will likely bottom out around -15F (or even a bit
colder) during the night with increasing south winds offsetting
the slow rise in temps. Some guidance trends suggest the
potential for some low-stratus development after midnight as
warm/moist advection flow increases above the shallow boundary
layer. Temperatures are expected to reach the upper 20s and
ending this short bout of very cold arctic weather.

The first in what appears to be a series of clipper-type
systems is forecast to propagate southeast across the northern
Plains and upper Mississippi Valley Friday afternoon/evening.
12/18Z guidance from Wednesday had waffled a bit on the track
and precip footprint with this system, though 00Z guidance is in
general agreement in bringing the positive-tilt mid-level wave
across the area Friday night with the primary surface low
passing north of the area. Forecast soundings depict rather dry
moisture profiles which mainly saturate in the mid-levels
briefly Friday evening. Ascent is not particularly strong and
the DGZ depth not impressive, suggesting the potential for a
period of mainly light snow, with QPF and ensemble precip probs
also notably low south of the IL/WI border. Have maintained
30-40% pops generally north of I-80 for this - highest toward
the WI state line and north of it.

Guidance remains in decent agreement with another mid-level
wave tracking east-southeast across the central/northern Plains
on a slightly farther south track Saturday, which looks to have
a better potential for producing some light snow across parts
of the forecast area Saturday night into Sunday, albeit in a
weakening phase. The clipper parade continues onward into next
week, with ensembles continuing to highlight systems Monday
night into Tuesday, and again Tuesday night into Wednesday.
There continues to be ensemble support for a deeper surface low
to track north of the area in the Wednesday time-frame,
potentially producing warm enough thermal profiles in which
mixed precipitation could be an issue over our cold snow pack.
Snow cover should remain largely in place, given cooler than
average temperatures expected through the period.

Ratzer

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1104 PM CST Wed Dec 3 2025

In the wake of an arctic cold front that crossed the area early
last evening, NW winds gusting to around 20 knots will
gradually diminish through the morning. Winds will then back SW
under 10 knots mid afternoon as a surface high pressure shifts
across northern Illinois. SW winds are then expected to persist
through tonight. VFR conditions are favored through the period,
though clear skies (at least initially) Thursday night and weak
low-level warm air/moisture advection may result in developing
BR/MIFG.

Kluber

&&

.CLIMATE...
Issued at 542 PM CST Tue Dec 2 2025

Updated at 250 PM CST Tue Dec 2 2025

Here are the current record low temperatures for Thursday into
Friday this week:

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 until 9 AM CST this morning for Winthrop
     Harbor IL to Gary IN.

     Small Craft Advisory until 3 PM CST this afternoon for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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