931
FXUS63 KLOT 220446
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1046 PM CST Fri Nov 21 2025

.KEY MESSAGES...

- Rain will continue to affect areas along and south of I-80
  through this evening.

- Another period of rain is likely (>80% chance) across the area
  late Monday into Tuesday.

- A modest warming trend is expected into early next week before
  temperatures turn much colder for Thanksgiving.

&&

.UPDATE...
Issued at 808 PM CST Fri Nov 21 2025

No significant changes to the going forecast this evening.

Rain continues across southern portions of the forecast area
approaching mid-evening, mainly near and south of the I-80
corridor. This rain has been occurring in association with a
strong but deamplifying mid-level short wave tracking along a
west-east oriented baroclinic zone north of a stationary front
stretching from southern MO into the Ohio Valley. The primary
mid-level vort center, evident in radar imagery across western
IL, will continue to propagate to the east over the next several
hours and will eventually exit the region after midnight. Rain
will thus end from west to east during the late evening and
early overnight hours as forcing for ascent shifts east. Colder,
drier air will filter in from the north, with decreasing cloud
cover across much of the forecast area by morning. Can`t rule
out some patchy fog/stratus development late tonight across our
south/southeast where rain has occurred, though these areas will
be last to clear out and low-level dry advection appears
substantial enough (along with some flow atop the boundary
layer) for these to be limiting factors.

Overall, going forecast appears to have these trends in good
shape through Saturday morning, an other than some minor
tweaking no significant changes appear needed.

Ratzer

&&

.DISCUSSION...
Issued at 310 PM CST Fri Nov 21 2025

Regional radar mosaic imagery this afternoon depicts an
elongated swath of precipitation extending from the central
Plains eastward through the Appalachian Mountains. Locally, this
precipitation is affecting areas along and south of the I-80
corridor. While a period of sprinkles could not be ruled out as
far north as the I-88 corridor this afternoon and evening, dry
low-level air impinging from the north should otherwise keep the
measurable rainfall suppressed to the I-80 corridor and points
southward through this evening. The precipitation will then end
during the late evening and early overnight hours as the primary
synoptic-scale forcing mechanism -- a sheared-out upper-level
shortwave trough -- peels off to the east. Up to a quarter of an
inch of rainfall could be observed when all is said and done
wherever the steadiest and most persistent rain ends up
occurring.

High pressure will settle into the region over the weekend as
today`s weather system vacates the area. A weak cold front
associated with an occluding surface low in Ontario will also
glide through the area Saturday evening. Column moisture looks
far too paltry for this frontal passage to be accompanied by
precipitation, but an upper-level northern stream shortwave
diving southeastward over the Great Lakes should result in a
brief uptick of mid- and upper-level cloud cover as it scoots
by. Saturday`s high temperature readings should end up being a
smidge milder than today`s highs in most locations. High
temperature readings should then inch upward yet again on Sunday
with the timing and overall strength of the cold front limiting
its ability to have a pronounced influence on Sunday`s
temperatures.

Sunday into Monday, an upper-level low will eject northeastward
out of the Desert Southwest. A strong ensemble QPF signal
remains across northern Illinois and northwest Indiana in the
late Monday through Tuesday time frame, and the NBM has
accordingly maintained categorical PoPs that peak Monday night.
With the continued gradual warming trend, air temperatures will
remain solidly above freezing throughout the duration of this
early week precipitation, so not expecting any precipitation
types aside from rain to come in to play.

A potent northern stream trough will follow closely on the
heels of this initial disturbance, reaching the Upper
Midwest/Great Lakes by mid-week. Some uncertainty remains
regarding how this trough will interact with the preceding
disturbance, which will affect the timing of its arrival, how
breezy winds will get, and whether its presence will lead to
another bout of precipitation here locally. At this time
though, the majority of Grand Ensemble members favor measurable
precipitation staying away from our CWA on both Wednesday and
Thanksgiving Day, so will continue to roll with the largely
sub-15% PoPs from the NBM for this time frame. One aspect of
higher forecast confidence towards the end of the current 7-day
forecast period is the arrival of a much cooler air mass for the
latter half of the week. Below normal temperatures thus appear
likely for the Thanksgiving holiday with highs largely favored
to be in the 30s and lows forecasted to fall into the 20s (and
possibly even the teens in some locations).

Looking beyond Thanksgiving, early indications are signaling
that a more active weather pattern will become established
across the central CONUS towards the end of November and into
the beginning of December. During this time frame, ensemble
guidance advertises deep mean troughing developing over the
western CONUS downstream of a prominent ridge over the northern
Pacific/Alaska, strong ridging setting up over the eastern
CONUS, and an energetic jet stream and sharp baroclinic zone
getting induced in between these two synoptic-scale features.
Time will tell what sort of sensible weather this pattern shift
will bring to our forecast area, but this certainly has the look
of a time period that will need to be monitored for impactful
weather systems affecting the central part of the country.

Ogorek

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1046 PM CST Fri Nov 21 2025

Forecast concerns include...

Patchy/shallow ground fog overnight.
Wind shift to northwest Saturday night.

Showers currently south of the terminals will continue moving
away from the area late this evening with dry conditions
expected through the period.

Some patchy or shallow ground fog is possible overnight into
early Saturday morning for areas away from Chicago. Confidence
remains low with the best chance for fog possibly favoring areas
well south of the terminals, but have maintained light/shallow
ground fog mention at RFD/DPA/GYY.

Light north/northwest winds are expected to become variable
overnight and then shift to the south/southwest Saturday morning
with speeds increasing to 10kt by midday. Speeds may increase
further to 10-15kt in the mid/late afternoon which may continue
into Saturday evening, along with some periodic higher gusts.
Wind directions will shift to the northwest later Saturday night
when a few gusts will also be possible. cms

&&

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

&&

$$

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