238
FXUS63 KLOT 011130
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 AM CDT Sat Nov 1 2025

.KEY MESSAGES...

- Isolated to widely scattered showers expected across northeast
  IL and northwest IN this afternoon and evening.

- Seasonable temperatures to persist through the weekend.

&&

.DISCUSSION...
Issued at 331 AM CDT Sat Nov 1 2025

Through Sunday:

An upper low continues to pivot across southern MN, IA, and WI
this morning and will be moving over IL later today. Analyzed to
the north of the upper low across central WI and Lower MI is a
cold front that will also move southward down the lake through
the day today. As the front moves into southern Lake Michigan
later on this morning it is expected to interact with an
elevated frontal zone that is lifting northward over southwest
MI and generate a meso-low over the lake. The convergence
associated with this meso-low and broad forcing from the upper
low is expected to generate an axis of isolated to widely
scattered showers. The showers will initially develop in
southern WI but will pivot into northeast IL this afternoon and
then eventually northwest IN this evening. Given that the
showers will mainly be tied to the aforementioned convergence
zone/meso-low, suspect rain chances will diminish with inland
extent from the lake so those in interior northern and north-
central IL and interior northwest IN will likely stay dry. In
addition to the showers, the modest lake induced instability and
surface convergence may allow for the development of a few
waterspouts especially over the open waters of the lake and the
IL nearshore. Otherwise, expect partly to mostly cloudy skies to
persist through this evening areawide with light west-northwest
winds and high temperatures around 50 degrees.

The meso-low is expected to gradually weaken this evening as it
pivots east and the upper low swings into the Ohio and
Tennessee River Valleys. Therefore, the associated showers are
expected to gradually taper through the evening with most
expected to be rain- free by midnight. Though, a few showers
could linger through the predawn hours Sunday morning in the far
northwest corner of Porter County. As the upper low departs, a
mid-level ridge will begin to build into the area which should
erode most of the cloud cover and allow temperatures to cool
into the lower to mid-30s (upper 20s possible in northwest IL)
overnight. Depending on how quickly clouds erode there is a
chance for some patchy fog (possibly freezing fog where
temperatures dip below freezing) to develop. Since there is some
uncertainty as to the speed the clouds erode and where the
greatest fog coverage will develop have opted to forego a formal
mention in the forecast at this time, but it appears the best
potential for fog will be south of I-80 and west of I-55
tonight.

Any fog that does materialize will erode by mid-morning Sunday
with otherwise mostly sunny skies expected. Winds will turn
southwesterly on Sunday as well which will allow temperatures to
rebound nicely into the mid-50s areawide.

Sunday night through Friday:

While we enjoy the tranquil weather on Sunday, the shortwave
trough currently entering the Pacific Northwest is expected to
be traversing across southern Canada and the northern CONUS.
Guidance continues to show a stout 100-150 kt upper jet
developing along the southern flank of the shortwave and nosing
into the trough axis allowing it to deepen as it moves into the
northern Great Lakes Sunday night. However, rain chances with
this shortwave have been backing off likely due to the lack of
sufficient moisture return into northern IL and northwest IN.
Since there is still expected to be some showers associated with
the shortwave in southern WI and Lower MI, cannot completely
rule out a stray shower or two brushes areas near the IL-WI line
and the lake Sunday night into early Monday morning (~20%
chance) but suspect most will remain dry. Regardless, the modest
pressure gradient and cold advection behind the shortwave still
looks to generate a period of breezy westerly winds on Monday
with gusts around 20-25 mph expected.

A surface high is generally expected to remain in control of
our weather through the middle of next week despite another
shortwave trough and weak cold front forecast to pivot through
the Great Lakes on Wednesday. Given that the surface high is
forecast to be centered to our south and east, it appears any
sufficient moisture return will be very limited and thus the
frontal passage on Wednesday should be mainly a dry one. Though,
a stay shower or two cannot be ruled out near the lake.
Otherwise, expect temperatures to remain near to slightly above
normal through next week with daily highs in the upper 50s to
lower 60s and nightly lows in the 30s and 40s.

Our next chance for notable rain does not look to be until a
series of storm systems towards the tail end of next week and
the following weekend. Though, there remains a great deal of
uncertainty in the strength of these systems and thus what
impacts they could bring to our area so stay tuned.

Yack

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 630 AM CDT Sat Nov 1 2025

And OVC cloud layer with bases around 060-070 will persist this
morning, although may begin to scatter with SCT-BKN deck around
040 developing later this morning and afternoon. Winds will
generally be westerly under 10 knots.

An area of showers will consolidate across southern Wisconsin
today and will eventually shift into northern Illinois this
afternoon and evening. Timing generally remains similar to the
previous set of TAFs, with the introduction of PROB30 groups for
lower cigs and vsbys at ORD/MDW this evening. Confidence in the
southward advancement of this area of showers remains low, but
it seems plausible activity will have a difficult time making
southward progress towards MDW and GYY. Winds may also get a bit
messy across the Chicago-area terminals as a lake-convergence
axis may end up developing in the vicinity.

Precipitation should tend to gradually diminish late this
evening. The main concern tonight into Sunday morning is the
potential for BR/FG development given light winds and and
increased near-surface moisture. The main uncertainty relates to
lingering cloud cover. If clouds clear out, BR/FG development
will become more likely. Confidence remains too low to justify
a formal mention of MVFR or lower vsbys at this time, but consideration
for lower vsbys may be needed in future TAF issuances.

Carlaw

&&

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

&&

$$

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