425
FXUS63 KLOT 122004
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
304 PM CDT Sat Jul 12 2025

.KEY MESSAGES...

- Other than a chance of some isolated-scattered showers this
  afternoon, and a few possible storms across central IL and IN
  Sunday afternoon, dry weather is expected through the rest of
  the weekend.

- After a couple day break Sunday and Monday, humidity returns
  mid-week along with chances of showers and thunderstorms.

&&

.DISCUSSION...
Issued at 304 PM CDT Sat Jul 12 2025

Through next Saturday:

A couple of weather features we are monitoring may provide parts
of the area with a few isolated to widely scattered late day
showers. The first is a mid-level impulse currently noted in the
water vapor imagery tracking east-northeastward across central
parts of IL. This feature will be the driver of some widely
scattered showers and possibly a few storms for the next few
hours across my far southeastern counties. The second feature is
a more robust northern stream impulse currently shifting out of
the Upper Midwest into the western Great Lakes. Increased
forcing for ascent in advance of this wave has been driving
scattered showers and storms to our north in WI just in advance
of an eastward shifting cold frontal boundary. The primary focus
for these showers is expected to largely remain to our north
through the late afternoon hours. However, there remains about a
20% chance for a few isolated late day showers across northern
IL as this cold front shifts into the area. Otherwise, a
majority of the area is expected to remain dry the remainder of
the day.

A less humid airmass will filter in across northern IL in the
wake of this front tonight into Sunday, with dewpoints falling
into the 60s. This less humid airmass will remain in place
through Monday. Accordingly, primarily dry weather is
anticipated for much of the area for Sunday and Monday. However,
we are keeping an eye on a small (~20%) chance for showers and
thunderstorms Sunday afternoon, particularly across central
parts of IL and IN (areas well south of the Kankakee and
Illinois River Valley). This is a change in the forecast as this
area now looks to remain close enough to the deeper moisture to
support another threat for some isolated to widely scattered
afternoon convection. Model guidance is also now in better
agreement in tracking what appears to be a convectively enhanced
impulse east-northeastward out across MO Sunday morning, then
into central parts of IL later in the day. Given this trend we
have opted to include a 20% mention for afternoon showers and
storms across far southern sections of the area. The main threat
from any storms in this area would be locally heavy downpours.

High pressure will scoot off to our east late Monday, with
southerly flow transporting the humid, Gulf air mass back
northward into the region Tuesday through Thursday. The main belt
of westerlies should remain to our northwest Tuesday and
Wednesday, though medium range guidance does hint at perhaps a
weak southern stream disturbance meandering northeastward into the
region supporting at least chances of primarily afternoon and
evening scattered showers and thunderstorms Tuesday and especially
Wednesday. By Wednesday night into Thursday, it looks like a
northern stream trough will push eastward across the Great Lakes
dragging a cold front across the area with the threat for more
showers and thunderstorms. Another day or two break from rain
chances and humidity looks possible Friday and perhaps into
Saturday.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1215 PM CDT Sat Jul 12 2025

Key messages for the 18Z TAF period include:

* Periods of MVFR possible early this afternoon

A densely SCT to BKN 2-3 kft deck is moving across the region
early this afternoon. Coverage should trend toward more
scattered moving through the afternoon, but bouts of MVFR cigs
will be possible for the first valid hour or two of the period.
Otherwise, VFR is expected throughout. A brief isolated shower
or storm cannot be ruled out this afternoon and again overnight,
but probs are far too low for a TAF inclusion. Expect
westerlies near or just over 10 kt subsiding to closer to 5 kt
this evening.

Doom

&&

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

&&

$$

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