576
FXUS63 KLOT 270542
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1242 AM CDT Sun Sep 27 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 /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1242 AM CDT Sun Sep 27 2026

Key aviation forecast messages:

- Patchy shallow fog (MIFG) may develop early this AM and again
early Monday AM, mainly outside of Chicago.

- Light and variable winds < 5 kt expected through midday then
turning NE up to 10 kt behind a lake breeze in the afternoon.

Dry and VFR conditions are forecast at the Chicago terminals
through the period. For outlying areas, a period of patchy
shallow fog remains possible early this morning and again early
Monday morning. Account for this with TEMPO groups for minor
VSBY reductions to low-end VFR and MVFR in the 9-13Z timeframe
for RFD, DPA, and GYY, though it is possible briefly lower VSBYs
to IFR/LIFR occur where high cloud coverage is lowest. Similar
conditions may occur again early Monday morning.

Winds through the remainder of the overnight and early morning
hours will be light and variable under 5 kt, eventually leaning
light NNW at ORD/MDW due to a weak land breeze. Winds then very
gradually trend back to the NNE through the morning remaining
mainly under 5 kt. A weak lake breeze will turn winds more
solidly northeast toward midday in the 5-10 kt range. Winds
ease again after sunset, eventually trending N to NNW under 5 kt
through early Monday morning.

Petr

&&

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

&&

$$

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