785
FXUS63 KLOT 160644
AFDLOT

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

.KEY MESSAGES...

- Scattered showers and thunderstorms will linger through
  Sunday morning. Torrential downpours and locally gusty winds
  will be possible with these storms and may result in renewed
  flooding in saturated areas.

- Chance for additional showers and thunderstorms Sunday
  afternoon, mainly southeast of I-55.

- Drier weather returns Monday briefly before storm chances
  increase midweek.

&&

.DISCUSSION...
Issued at 144 AM CDT Sun Aug 16 2026

A shortwave trough continues to pivot across northern IL and
has lead to the development of a cluster of thunderstorms. This
cluster of thunderstorms will continue to push east across
northwest IN through the early overnight hours before exiting
our area. The main threat with this storm cluster will be
torrential downpours, but some localized pockets of gusty winds
(upwards of 45-50 mph) have been occurring and that will likely
continue as the cluster moves across our northwest IN counties.
Given that this cluster is moving rather quickly, the flooding
threat with it appears to be low.

In the wake of this cluster, light to moderate stratiform
showers will persist through the predawn hours. However,
additional showers and thunderstorms are developing in northern
MO and west-central IL along the remnant outflow boundary from
last night`s storms. Latest radar trends show that these
developing showers/storms may stay just south of our forecast
area, however, if any development can occur further north then
portions of Livingston, Ford, and Iroquois Counties would be in
play. Given that the steering flow and forcing are oriented
parallel to the outflow, showers/storms in central and north-
central IL will likely train over the same areas. Couple this
with the 2.0 inch PWATs and the modest instability and
conditions are primed for another period of torrential rainfall.
If the heaviest rainfall does occur over our southern areas,
then a threat for significant flash flooding would quickly
materialize as these areas have already seen nearly 6-10 inches
of rain over the past few days. Due to this threat a Flash Flood
Watch was issued earlier this evening and remains in effect
until 10 AM CDT this morning for areas near and south of I-80
where the flooding threat is greatest.

The showers and storms tonight are expected to gradually wane
around daybreak as the low-level jet weakens and the
aforementioned shortwave pushes east of the area. However, a
cold front (which is currently analyzed along a Sioux City, IA
to Minneapolis, MN line) will be moving across northern IL and
northwest IN today. Initially, it looks as if the atmosphere
should be stable enough to keep dry conditions around through
much of the morning, but another shortwave is expected to pivot
across southern IA and north-central IL this afternoon. As this
wave approaches the front is forecast to be near the I-55
corridor which is where the focus for additional showers and
storms this afternoon should reside. That said, forecast
soundings do continue to show some weak capping in place and
with the bulk of the wave`s forcing forecast to be aimed into
central IL it seems shower and storm coverage locally will be
more hit and miss. For now have opted to maintain some 20-30%
chances for showers and thunderstorms in the forecast, mainly
for areas southeast of I- 55, but suspect many locations should
remain dry especially those to the north of I-55. Regardless,
the threat for severe weather with any storms today is low due
to the lack of wind shear though heavy downpours and locally
gusty winds will still be possible.

The cold front should move through our area this evening
allowing a surface high to start building in from the north.
This building high will finally break us out of this stormy
pattern for Monday and most of the day on Tuesday. Therefore,
expect mostly to partly sunny skies both days with highs in the
low to mid-80s and overnight lows in the 60s. Unfortunately, the
nice weather won`t last long as another shortwave and its
associated cold front are forecast to dive through the Midwest
Tuesday night into the day on Wednesday. This system will bring
more chances for showers and thunderstorms to the region as
early as Tuesday evening, but the bulk of the stormy weather
should occur overnight Tuesday night into Wednesday. While
confidence is high on showers/storms occurring during this
period, there continues to be some uncertainty in exact timing
and intensity so make sure to stay updated as we get closer.

On the bright side, long range ensemble guidance continues to
hint that high pressure should move in behind Wednesday`s storm
system which looks to keep the bulk of any additional storms
south and west of us for the later half of the week. Though if
this does occur it looks as if temperatures may be more on the
seasonably cool side with highs in the 70s and lows in the 50s
to 60s.

Yack

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 100 AM CDT Sun Aug 16 2026

Key aviation forecast messages:

- Period of TS through 7-8Z with steady rain lingering through
  9-10Z, may arrive with a gusty SW wind shift to 25-30kt

- IFR CIGs and MVFR VSBYs in BR may develop early this morning
  behind the SHRA (LIFR CIGs/IFR VSBYs at RFD).

- Breezy WNW winds through the day turning NNW late afternoon

A broken arc of gusty thunderstorms will race across the Chicago
area terminals over the next 1-2 hours bringing gusty winds,
localized downpours, and associated VSBY reductions. Winds may
gust up to 25-35 kt out of the southwest along the leading edge
of the storms. Expect the main TS threat to end within 1-2 hours
of storm onset with steady rain potentially lingering for
another 1-2 hours, ending by 10Z or so. CIGs in the wake of the
showers will likely drop to IFR for much of the area (LIFR
toward RFD) early this morning along with reductions in VSBYs in
BR. Gradual improvement is then expected through the morning
hours back to VFR toward midday.

Winds will turn WNW after daybreak with occasional gusts into
the 15-20 kt range expected through the afternoon. A cold front
then sweeps across the area mid to late afternoon and may bring
a brief period of showers and isolated TS, though confidence
remains too low to include in the TAFs with this update (<30%
chance). Winds then turn NNW in the wake of the front with gusts
easing after sunset.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 10 AM CDT this morning for ILZ019-ILZ020-
     ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ105-ILZ106-ILZ107-
     ILZ108.

IN...Flood Watch until 10 AM CDT /11 AM EDT/ this morning for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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