418
FXUS63 KLOT 162329
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
629 PM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Isolated to scattered thunderstorms may develop along a cold
  front into this evening. Locally heavy rainfall is possible
  with these storms.

- Drier weather is in store Monday into Tuesday before storm
  chances return midweek.

&&

.DISCUSSION...
Issued at 104 PM CDT Sun Aug 16 2026

The primary forecast concern this afternoon and evening is the
potential for isolated to scattered, heavy rain-producing
thunderstorms ahead of an approaching cold front. This front,
currently located across southern Wisconsin, will move southward
into northern Illinois during peak heating this afternoon.
Despite mostly cloudy skies, occasional breaks will support
modest surface heating and the gradual destabilization of the
very moist, prefrontal airmass. Accordingly, as capping
continues to weaken this afternoon, isolated showers and storms
are expected to develop. Given limited surface convergence
along the boundary, storm coverage should remain isolated to
widely scattered for the next few hours. However, coverage may
increase along the front late this afternoon and into the
evening as forcing for ascent strengthens in response to a
remnant MCV moving east out of southern Iowa. If this occurs, it
would likely impact portions of the Chicago metro area and
northwestern Indiana between 4 p.m. and 9 p.m. While the threat
of severe weather remains low due to poor mid-level lapse
rates, some locally gusty surface winds up to 50 mph could
occur, particularly where storms cluster. Of greater concern are
the torrential downpours likely to accompany these storms,
which could result in localized flooding, especially if multiple
storms track over the same areas of the Chicago metro.

We will see an end to our chances for showers and thunderstorms
with the passage of this front this evening. Surface high
pressure will settle over the Mid-Mississippi Valley on Monday.
Lower humidity and slightly cooler temperatures (highs around
80) will provide a brief reprieve from our active weather
pattern of late, before another round of convection arrives late
Tuesday afternoon and night. This next system, driven by a cold
front and shortwave digging into the Great Lakes, brings a
renewed threat of strong storms and heavy rain Tuesday night.
Quieter, cooler weather (temperatures in the 70s) returns for
the second half of the work week.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 629 PM CDT Sun Aug 16 2026

Forecast concerns for the terminals...

- Scattered showers and thunderstorms possible, mainly south of
  I-80, through mid-evening.

- Northeast wind shift at the Chicago area terminals Monday
  morning with a lake breeze.


A cold front is progressing across far northern IL this evening
and will continue to drift through the rest of the area this
evening. Ahead of the cold front, a shortwave trough is pivoting
out of southeastern IA and has lead to the development of some
scattered showers and thunderstorms in western IL. The
expectation is for these scattered showers/storms to stay south
and west of the terminals and mainly be an issue for areas near
and south of I-80 (roughly a VYS to VPZ line). Though, given the
trajectory of the ongoing showers/storms in Lee County, IL
cannot rule out a shower or storm getting to DPA, MDW, or GYY
between prior to 03z. Regardless, once the cold front pushes
through this evening any showers/storms should get pushed south
of northern IL and northwest IN giving as a dry night.

Winds will remain breezy (speeds around 10-12 kts) out of the
west-northwest through the evening before becoming solidly
northwest behind the front. While winds should diminish
overnight, speeds look to remain in the 5-7 kt range overnight
into Monday morning.

Dry conditions are expected to prevail through Monday with
otherwise VFR conditions. However, guidance continues to be
adamant on a plume of lake effect clouds developing over the
Chicago terminals and GYY which could result in a period of MVFR
(2000-2500 ft) ceilings. With moisture depths on the forecast
soundings looking modest confidence on MVFR ceilings is low so
have opted to maintain the SCT025 mention for now. That said, if
the MVFR ceilings do materialize cannot rule out an isolated
sprinkle with them either. Otherwise, expect north winds around
5-10 kts to prevail through Monday afternoon inland with
northeast winds at the Chicago terminals and GYY. Though wind
directions will veer towards a southwesterly direction late
Monday afternoon and evening.

Yack

&&

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

&&

$$

Visit us at weather.gov/chicago