323
FXUS63 KLOT 021802
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1202 PM CST Mon Feb 2 2026

.KEY MESSAGES...

- Untreated surfaces such as sidewalks, parking lots, and
  roadways across interior northwestern Illinois may be slick
  after patchy freezing drizzle early this morning.

- Another clipper system will move through the area tonight with
  a 20% chance for a quick coating of snow at any given location
  (most areas should stay dry).

- Lake effect snow showers may meander across the northeastern
  Illinois and northwestern Indiana shores of Lake Michgian
  Tuesday night into Wednesday morning (currently a 20%
  chance for a dusting of snow).

- Temperatures will make a run for the freezing mark toward the
  end of the week, marking the end of a prolonged stretch of
  daily highs below 32 degrees. (Could be close to tying 15th
  longest stretch below freezing at both Chicago and Rockford).

- A pattern change toward warmer temperature (highs and lows
  both above freezing) may materialize by the middle of next
  week.

&&

.DISCUSSION...
Issued at 238 AM CST Mon Feb 2 2026

Through Tonight:

The central axis of a sheared-out upper-level shortwave is
passing over northern Illinois and northwestern Indiana at press
time. While snow with the system largely underperformed (a
consequence of nebulous forcing for ascent offset from a narrow
DGZ), a ribbon of freezing drizzle and fine mist apparently
tied to modest WAA within the low-level stratus layer ahead of a
weak cold front has proved resliliant while moving across
north-central Illinois early this morning. Observations of
ceilings and visibilities, as well as areal webcams, depict the
most persistent freezing drizzle along and north of Interstate
88 and especially toward the Wisconsin state line. Will go
ahead and issue a Special Weather Statement for Winnebago, Ogle,
Lee, DeKalb, Boone, McHenry, and Kane counties to highlight the
threat for untreated surfaces (such as roadways, parking lots,
and sidewalks) to become icy this morning. With radar returns
gradually decreasing as the shear axis shifts east of our area,
the intensity of the freezing drizzle/mist should weaken toward
Lake Michigan. All precipitation should cease by daybreak.

The next forecast items of concern are cloud and temperature
trends today. Recent nighttime microphysics imagery depicts
quite an expansive bank of low-level stratus extending back
toward the Minnesota and South/North Dakota borders. Positive
mid-level height tendencies atop a broad surface high pressure
system moving across the northern Great Lakes point toward
lowering inversion heights today, which would typically suggest
that stratus will eventually scatter out. Of course, the speed
at which this process takes place during the cool season is
often wrought with uncertainty, as low-level stratus decks have
a way of overstaying their welcome. In spite of a few holes in
stratus starting to emerge across central Minnesota, will go the
pessimistic route and advertise mostly cloudy across our area
today. When combined with modest cold air advection, will
advertise a relatively muted influence of the diurnal cycle on
temperatures today with highs in the mid to upper 20s (just 5
to 7 degrees warmer than where temperatures are now).

Tonight, The clipper system currently meandering along the
Montana/Canadian border will slip southeastward and pass through
the Lower Great Lakes. In the absence of meaningful low-level
moisture advection ahead of the wave (and in fact, northerly
surface flow will be transporting low-level dry air into the
Lower Great Lakes), chances for widespread snow with the clipper
locally look pretty slim (<20%). With that said, forecast
soundings and omega profiles from an ensemble of short-term
model guidance depict lift and relatively steep lapse rates
centralized in the DGZ as the system passes through, raising
concern for a sneaky threat for a narrow band or two of
snow with localized accumulations of up to an inch or so. Like
forecasting convection in the summertime, it`s difficult to
pinpoint exactly where any streaky snow elements may develop 24
hours out. So, will offer broad-brushed low (20%) PoPs across
the entire area tonight keeping in mind most areas probably
won`t see a snowflake.


Tuesday through the upcoming weekend:

A surface high pressure system will build into the Great Lakes
on Tuesday, helping clear any remaining clouds. Another push of
modest cold air advection will hold afternoon high temperatures
in the mid to upper 20s.

Tuesday night into Wednesday, somewhat disorganized aggregate
upper-level troughing will redevelop across the Midwest/Great
Lakes region anchored by several embedded shortwaves. One of the
more dominant shortwaves appears poised to spur the development of
a low pressure system somewhere in the lower Ohio River Valley,
which in concert with the surface high pressure system centered
in the Upper Great Lakes will set the stage for developing low-
level convergence and lake effect snow across the southern shore
of Lake Michigan. Depending on the eventual flow configuration
that materializes between the surface high and low pressure
systems as well as any augmentation by land breezes originating
offshore of Lower Michigan, the lake effect snow could sneak
into northeastern Illinois including into Chicago. With none of
the upper-level shortwaves embedded in the cyclonic flow aloft
currently expected to pass directly over Lake Michigan,
inversion heights will remain pretty stunted and near or even
below 5kft. As a result, the lake effect snow that develops will
be more of a nuisance than anything else (certainly nowhere
close to as intense as the past few lake effect snow events),
with a few tenths of an inch to locally half an inch of snow
expected generally within a 12 to 18 hour period. So, will
continue to manually add low PoPs (20-25%) centered on the
southwestern shore of Lake Michigan for the Tuesday night into
Wednesday timeframe. Notwithstanding the lake effect snow
showers, Wednesday looks pretty quiet otherwise with highs in
the 20s.

Ensemble model guidance is in growing agreement that a clipper
system will dive southward from central Canada and into the
Great Lakes toward the end of the week. Aggressive warm air
advection ahead of the clipper may allow for temperatures
locally to reach the freezing mark Thursday or Friday, which
would be the first time in 21 or 22 days (tying somewhere
around the 15th longest stretch of temperatures below freezing
at both Rockford or Chicago). Conceptually, would expect a quick
hit of snow (or rain) with the clipper system, but exactly
where will come down to the eventual track. A pool of seasonably
cool air will anchor the clipper system, setting the stage for
temperatures to fall by this weekend. Will note there is a
signal for another clipper system sometime in the next
Sunday/Monday timeframe in the general region, too.


Next week:

Looking toward next week, ensemble model guidance exhibits a
strengthening signal that the exceptionally persistent
northwesterly upper-level flow pattern that has thus far
defined winter across the central/eastern United States may
temporarily break. As a result, ensemble mean temperatures
trend notably upward by the middle of next week and beyond, with
both high and lows above the freezing mark. Indeed, the CPC
temperature outlooks for the middle of February favor the above
average category across much of the central US.

Also have to point out a growing signal for a southwest-flow
synoptic scale cyclone somewhere east of the Rocky Mountains in
the February 11-14 timeframe, with both the GEFS/EPS already
favoring our area being on the warm side. Should a cyclone
actually develop and we end up on the warm side, could easily
envision forecast focus trending toward hydrology concerns
considering the frost depth of just deeper than 13 inches at our
office isn`t going to vanish anytime soon.

Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1202 PM CST Mon Feb 2 2026

Key Messages:

- MVFR ceilings will continue to be observed this afternoon
  before scattering out.

- There is roughly a 25-35% chance for a period of snow to be
  observed overnight tonight.


MVFR stratus continues to blanket the area early this
afternoon. Some flurries have been leaking out of this cloud
deck as well, and this may continue to be the case while the
stratus remains in place. Between the back edge of the stratus
approaching the terminals and the stratus thinning/eroding, a
return to VFR conditions is likely this evening. However,
lake-induced MVFR stratocumulus will make an inland surge
sometime tomorrow morning, bringing a renewed period of MVFR
ceilings to GYY, MDW, and possibly ORD tomorrow.

There also remains about a 25-35% chance for snow at the
terminals overnight tonight as a mid/upper-level shortwave
disturbance dives into the region. There is an increasing
likelihood that there will be a narrow corridor somewhere in the
area where the snow comes down at a fairly decent clip --
enough to reduce visibility lower than presently advertised in
the going TAFs. However, the greatest likelihood for this
appears to be south and southwest of the terminals, so only have
visibility reductions down to MVFR in the going PROB30 groups
at this time.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago