379
FXUS63 KLOT 262330
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 PM CDT Sat Sep 26 2026

.KEY MESSAGES...

- Seasonable temperatures for late September are expected over
  the next several days.

- The next chances for widespread rainfall are forecasted to
  come mid to late next week.

&&

.DISCUSSION...
Issued at 203 PM CDT Sat Sep 26 2026

A ridge of high pressure continues to reside over the Great
Lakes in between the Nor`easter off the east coast and the broad
troughing over the Pacific Northwest and Mountain West regions.
This ridge is expected to remain in place through at least
Monday which will keep seasonable temperatures (highs in the
upper 60s to lower 70s and lows in the upper 40s and 50s) and
primarily dry conditions around locally. However, there has been
a band of some light showers and sprinkles in eastern IA
associated with a shortwave disturbance rounding the base of the
aforementioned western trough. While these showers/sprinkles
will likely drift eastward tonight, the persistent east-
northeast winds should keep drier air in place and prevent much
of these showers/sprinkles from reaching the ground. That said,
have opted to maintain a 10-20% chance for an isolated sprinkle
near and west of I-39 late tonight into early Sunday morning
just in case. Additionally, there is a chance for some patchy
fog to develop around daybreak Sunday morning, mainly in
northwest IN and adjacent areas of northeast IL. Given that
cirrus clouds from the aforementioned showers in IA will spread
east tonight, it is unclear how widespread and dense the fog
will be as the clouds should help to ease some of the
radiational cooling. For now have introduced some patchy fog to
the forecast in northwest IN and portions of northeast IL where
cloud cover is forecast to be at a minimum.

By Tuesday the broad trough over the Pacific Northwest and
Mountain West is forecast to be ejecting into the upper Midwest.
As it does so another trough/closed upper low is forecast to be
traversing across southern California and the southwest CONUS.
Latest ensemble and deterministic guidance favors that these two
features will remain separate from one another which means that
the Pacific Northwest trough should arrive first and bring with
it some rain showers for the Tuesday night into Wednesday night
timeframe. The southwestern trough/low is then expected to lag
and arrive sometime towards the Thursday into Friday timeframe
with additional showers and perhaps even some thunderstorms.
However, it should be noted that guidance has been varying on
the exact arrival time of these troughs and their associated
rain thus making the specifics of this part of the forecast
lower confidence. Despite the uncertainty, a period of wet
weather looks likely mid to late week.

Behind these troughs, guidance is even more uncertain as to
whether or not the upper level pattern will become more zonal
(east-west oriented) or remain amplified heading into next
weekend. If the zonal pattern becomes reality then we could be
looking at another period of tranquil weather for next weekend,
but if the amplified pattern materializes then things could
remain active. With the large amount of uncertainty confidence
beyond Thursday is obviously very low, but something we will be
keeping an eye on. Regardless, seasonable temperatures are
forecast to remain through at least next week.

Yack

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 630 PM CDT Sat Sep 26 2026

VFR conditions will prevail through the period with the
exception of BR/MIFG at outlying sites (DPA, GYY, RFD) late
tonight through sunrise Sunday. Plenty of passing upper-level
cirrus may mitigate the BR/MIFG potential, but if the cirrus
clears more than expected tonight, a brief period of LIFR or
lower visibility cannot be ruled out around sunrise for the
outlying sites.

ENE/NE winds under 10 knots at TAF issuance will slowly
diminish this evening. A land breeze developing over northeast
Illinois overnight is expected to shift winds NW around or under
5 knots late tonight into mid-morning Sunday for the Chicago
terminals. Winds should then return NE by late morning, then
exhibit a lake-enhanced increase up to 10 knots early in the
afternoon.

Kluber

&&

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

&&

$$

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