984
FXUS63 KLOT 021119
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
619 AM CDT Thu Oct 2 2025

.KEY MESSAGES...

- Dry and unseasonably warm daytime conditions to persist
  through the weekend.

- Monitoring an increased fire danger this weekend, but
  primarily on Sunday.

- A much cooler airmass arrives middle to end of next week.

&&

.DISCUSSION...
Issued at 205 AM CDT Thu Oct 2 2025

While ridging will be replaced by low amplitude troughing over
the region today, this won`t result in much change to our
weather as deeper moisture will remain well to our west. Some
diurnal cumulus development appears possible this afternoon
across our I-39 corridor locales where PBL mixing into some
lingering 800 mb moisture will occur, but warmer air around 700
mb should keep any Cu fairly flat with any deeper buildups and
sprinkle/light shower chances farther to the south and west.
Temperatures will jump a few degrees today, most notably across
northeast Illinois where the inland push of the lake breeze
influence will be more limited than on Wednesday. Highs will be
in the mid to locally upper 80, and in the upper 70s/near 80
across the Illinois lakefront.

Somewhat deeper southwesterly flow will establish across the
area on Friday. This will drive a very modest increase in
boundary layer moisture northward which in turn should
facilitate the development of a more expansive afternoon Cu
field. Some guidance suggests a lingering warm layer around
700-600 mb will cool sufficiently to potentially carve out a 100
J/kg or so of surface CAPE during peak heating in spots. Can`t
totally rule out a few sprinkles developing out of any deeper Cu
deck, but chances for this seem a bit too negligible to
incorporate a mention into the gridded forecast at this point.
Temperatures will likely warm a degree or three as well, with a
few 90 degree readings not out of the question.

Precip chances over the weekend remain quite low, with deep
mixing and subsidence warming aloft leading to warm, dry, and
breezy conditions. The main focus remains on dewpoint, RH, and
wind trends. Latest guidance trends continue to suggest that
dewpoints will likely mix out more aggressively compared to
Friday, with Sunday currently looking like the driest of the two
days. Afternoon RH values in the 30-40 percent range on
Saturday and then 25-35 percent range on Sunday look pretty
reasonable at this range, with some potential for these to come
down a bit further depending on the degree of mixing. Southerly
wind gusts up to 25 mph are possible Saturday and then about 30
to perhaps 35 mph on Sunday, strongest north and west of I-55
and across northwest Illinois within a belt of stronger BL
flow. Will continue to highlight an elevated fire danger both
days as a result, but Sunday obviously is the greater concern at
this time. At this point, it looks like we`ll probably stay shy
of Red Flag conditions.

A strong cold front will push through the region during the
Monday-Tuesday timeframe. An initial boundary/pre-frontal
trough/composite outflow will approach the region on Monday,
possibly with an initial batch of showers. Most guidance
indicates temperatures will warm back into the 80s across most
of the area Monday afternoon before the main frontal zone slips
through later on Tuesday. While mid-level lapse rates and
associated instability looks unimpressive ahead of the front
Tuesday afternoon, stronger deep-layer flow will arrive through
the day, and if some muted insolation is realized, it wouldn`t
be totally out of the question for a few stronger thunderstorms
ahead of the surging cold front. A faster FROPA would tend to
diminish this potential. Ascent will continue atop the frontal
inversion into Tuesday night, leading to a chance for lingering
anafrontal showers and perhaps a few thunderstorms before things
dry out on Wednesday.

A much cooler airmass will remain in place through the end of
next week. Low temperatures Thursday morning generally in the
40s are expected, with a chance for a few upper 30s in typical
cool/sheltered spots.

Carlaw

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 619 AM CDT Thu Oct 2 2025

There are no aviation weather concerns for the 12Z TAF period.

SEs this morning will veer to S by late morning, possibly even
going 190-200 for a brief period, before a lake breeze pulls
them back to ESE this afternoon, largely below 10 kt all the
while. Direction will then go SSW overnight into Friday. Expect
VFR through the period.

Doom

&&

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

&&

$$

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