867
FXUS63 KLOT 142340
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
640 PM CDT Tue Oct 14 2025

.KEY MESSAGES...

- Some scattered showers expected late tonight into Wed morning,
  mainly north of I-80.

- A period of showers and possible thunderstorms is expected
  late Friday night or Saturday.

&&

.DISCUSSION...
Issued at 214 PM CDT Tue Oct 14 2025

Weak shortwave trough over Nebraska this afternoon will track
eastward across the Cornbelt and western Great Lakes tonight
into Wednesday morning. Forcing is not progged to be
particularly impressive, but mid-upper level height falls in
conjunction with some modest isentropic ascent on the 295-300K
surfaces should be enough to support some scattered showers
later tonight into Wednesday morning. Greatest coverage should
be north of I-80 and especially closer to the IL/WI border. Low
level moisture/cloudiness could get trapped beneath a sharpening
frontal inversion Wednesday, so much of the day could end up
socked in cloud cover. The cloud cover should help keep temps
noticeably cooler than today, though there could be a sharp
temperature gradient near or over our southern/southwestern CWA
where skies could clear out earlier.

While there are some differences in smaller scale details with
time, guidance is largely in agreement on a transition to a more
active, progressive and fairly amplified longwave pattern over
North America late this week through at least the first half of
next week. This should result in more frequent rain chances
along with some typical autumnal temperature swings.

As upper low and longwave trough over the West Coast today moves
eastward, look first for upper ridging to build east into the
area later this week with a warming trend Thursday and
especially into Friday. As the trough and accompanying cold
front move across the area later Friday night or Saturday, it
should be accompanied by showers and possibly a few
thunderstorms. A much cooler (though fairly seasonable) air
mass will filter into the area in the wake of the front Saturday
night through Monday.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 640 PM CDT Tue Oct 14 2025

Aviation forecast concerns focus mainly on a period of showers
late tonight into Wednesday morning, with some patchy MVFR
conditions possible. Breezy northeast winds are also likely
tonight into early Wednesday, with some sporadic gusts as high
as 20 kt possible.

Surface high pressure was centered north of the area across the
upper Midwest early this evening, with northeast winds across
the forecast area. The cold front which sagged through the area
late yesterday has become somewhat indistinct to the south of
the terminals, from far northern MO into central IL. A mid-
level disturbance will lift northeast from the Plains into the
upper Mississippi Valley tonight into Wednesday morning, which
will result in showers developing north of the warm front from
IA into MN/WI, though it appears there will be sufficient
moisture and support across far northern IL to provide a period
of showers across this area as well from late tonight through
mid- late Wednesday morning. Coverage looks to be highest
roughly in the 3 am to 9 am window, when some patchy MVFR
conditions are possible. Showers should then decrease in
coverage and end by early afternoon.

With the surface high centered to our north, northeast winds
will increase into the 10-15 kt range this evening and may
sporadically gust 15-20 kts overnight as an east-northeasterly
low level jet develops above the boundary layer. These winds
should ease by mid-morning Wednesday, while generally remaining
northeast through the period.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 1 PM CDT Wednesday for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CDT Wednesday for the IN
     nearshore waters.

&&

$$

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