710
FXUS63 KLOT 040829
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
229 AM CST Tue Nov 4 2025

.KEY MESSAGES...

- Seasonably mild, frequently breezy, and dry through midweek.

- The best chance for measurable rain this workweek will be
  late Thursday night into Friday morning.

- Temperatures will turn sharply cooler this weekend into early
  next week.

&&

.DISCUSSION...
Issued at 229 AM CST Tue Nov 4 2025

Moisture channel loops reveal a well-defined, but fairly low-
amplitude and compact shortwave pressing eastward across
Nebraska early this morning. This feature will approach the
region later this morning and afternoon, and will encourage a
southwesterly low-level mass response and an associated increase
in warm advection. As this takes place, ribbons of increased
mid and upper-level cloud cover will develop yielding generally
partly sunny conditions, at least until mid-late afternoon after
which skies will (temporarily) clear. Some modest 850-700 mb
frontogenesis is noted in recent guidance, but forecast
soundings look unimpressive from a moisture/ascent perspective,
with a very dry sub-cloud layer likely to sublimate away any
high-level precip before reaching the ground. The latest ECMWF
continues to crank out a few sprinkles south of I-80 towards
midday, but even this currently looks aggressive based on its
forecast soundings.

Once again, have made significant cuts to dewpoints from the
NBM gridded guidance, particularly across the northeast 2/3rds
of the forecast area this afternoon. Forecast soundings reveal a
plume of very dry air present right around 800 mb, with
analyzed dewpoints in the -30 to -40 C range (the 00z DVN
sounding shows nearly -50 C in this layer!). Even with a bit
more muted insolation compared to yesterday, with surface
dewpoints at this hour still only in the mid/upper 20s, have cut
afternoon values down towards the UKMET, ECMWF, and WRFARW, all
of which performed fairly well yesterday afternoon
(HRRR/RAP/GFS combo as expected were much too dry). This yields
minimum RH values once again down near or locally under 25
percent. Winds don`t look nearly as strong as they were
yesterday, and it`ll take some time for the morning inversion to
mix out (possibly not until after 1 pm). Also, there will also
likely be a mismatch between the diurnally-strengthening
southerly breezes late this afternoon as low-level moisture
surges northward across the region. As a result, think we`ll be
okay holding off on another Special Weather Statement for
increased fire concerns today, but will message a slightly
elevated potential in the Fire Weather Forecast.

Tonight, it`s deja vu all over again as another surface low
shifts east across the Great Lakes and drags an impressive LLJ
northward. Intermittent gusts over land will increase to around
25 mph, and a bit higher over the lake. The warm advection wing
tied to this surface low looks parched of any moisture of
consequence, with just some briefly increased cloud cover
tonight. The attendant cold front will slice through the area
Wednesday morning, this time with notably more cold advection
compared to yesterday`s system. Have boosted winds and gusts
given indications of deeper mixing towards 850 mb and mean
boundary layer flow pushing 25-30 knots. This should yield a
quick increase in wind speeds through mid-late morning, with
gusts around 35 mph, perhaps intermittently up to 40 mph. Winds
will then ease through mid- late afternoon.

After a chilly start Thursday morning, warming southerly breezes
will return again Thursday afternoon as the next surface low
develops across northern Minnesota and Lake Superior. While the
deepest moisture will remain to our north, strong forcing for
ascent and increasing mid-level instability will facilitate a
blossoming area of showers and possibly a few embedded
thunderstorms Thursday night into Friday morning.

Depending on how fast things trend, it`s possible we`ll manage
to squeeze out another day with highs in the upper 50s/lower
60s Friday, but another cold front will eventually shift through
the area, dropping temperatures back into the 40s and 50s on
Saturday. The ensemble signal for another--potentially somewhat
robust--surface low spinning up in the vicinity of the remnant
baroclinic zone continues to increase. All of the major
ensemble systems depict a smattering of near/sub 1000-mb surface
lows tracking east across either central or northern Illinois
on Saturday night. While some produce a swath of accumulating
wet snow across parts our region Saturday night into Sunday,
these currently remain more the exception than the rule, and
tied to deeper and farther south solutions. However, the
potential for rain to mix with or change over to snow within the
deformation zone is possible as a surge of much colder air will
be spilling in from the north during this period. At this time
frame, elected to limit any snow mention to a slight chance
across parts of interior northern/northwest Illinois given the
still somewhat modest signal for wintry precip, but something
that will certainly need refining over the next few days.

A much colder airmass will press into the area through Sunday
and Monday, with some degree of lake effect precipitation
(probably mostly rain at the immediate lakeshore, but
potentially transitioning to snow Sunday night/Monday AM inland)
developing into parts of northwest Indiana.

Carlaw

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1058 PM CST Mon Nov 3 2025

Light southwest winds will prevail through the overnight and
morning hours. High clouds will pass overhead through the
morning hours as a moisture-starved and weakening system slings
overhead. As high clouds thin toward noon, mixing heights should
build sufficiently to allow a few wind gusts up to about 20kt
out of the southwest.

After sunset, surface decoupling will encourage winds to back
toward the southeast for a few hours (wind direction 170 or
so). The wind direction should veer back southwesterly with time
as a strong low-level jet develops overhead. LLWS criteria will
be met from 03Z onward as flow at 2kft reaches 45 to 50kt.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 7 PM this evening to 6 PM CST
     Wednesday for Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from 7 PM this evening to 3 AM CST
     Thursday for Gary to Burns Harbor IN-Burns Harbor to
     Michigan City IN.

&&

$$

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