657
FXUS63 KLOT 200137
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
837 PM CDT Wed Aug 19 2026

.KEY MESSAGES...

- Scattered thunderstorms will continue this evening well south
  of I-80.

- Storms this evening will be capable of locally torrential
  downpours which could result in localized flash flood threat.

&&

.UPDATE...
Issued at 837 PM CDT Wed Aug 19 2026

There were a few reports of funnel Clouds in Livingston, Ford,
and Iroquois Counties this evening, but as sunset has passed,
funnel cloud activity is not expected the rest of the night.

Generally, showers and storms have behaved in our area, with the
focus more to the south and west of US-24. However, storm
motions are very slow, around 5 to 10 mph to the southeast.
Coverage is slowly expanding for areas south of the Kankakee
River. A targeted area north of Cissna Park received 2 inches of
rain in an hour on MRMS, and another appears to be developing
southeast of Thawville. While coverage of the torrential rain is
more isolated, given the already saturated soils a Flood
Advisory was issued for southern Iroquois County. While storm
motions are slow, the footprints of the heaviest rainfall rates
have been quite small, lowering the confidence in the need for
a Flash Flood Warning. That being said, we are also monitoring
an axis of better coverage of rain moving into southern
Livingston and eventually into Ford County where localized 1"+
per hour rain rates are being observed south of Pontiac.

DK

&&

.DISCUSSION...
Issued at 233 PM CDT Wed Aug 19 2026

Through Tonight...

Showers and thunderstorms should tend to gradually weaken by
mid evening as the area of showers/storms pushes gradually south
of the area as diffuse front pushes slowly southward. Behind
the front, skies will clear some tonight with light winds and
still a fairly moist boundary would suggest that there could be
some fog again late tonight into early Thursday morning. Best
chance of clearing and light winds is over western CWA, so hit
the fog the hardest in this area in the grids.

- Izzi

Thursday through Wednesday...

By early tomorrow, the stationary front and associated broad
low pressure center will be moving away to the east making room
for relative high pressure to slide over the region. The dry
airmass will bring mostly sunny skies to tomorrow while
afternoon temperatures look to peak in the upper 70s to near 80
degrees. The quiet pattern will be short-lived, however, as
another trough axis is progged to swing across the Midwest late
tomorrow night through Friday. A surface cold front will drop
across the area on Friday bringing shower and thunderstorm
chances.

Some pre-frontal activity will be possible in our northwest
during the morning hours. Greatest chances will be during the
afternoon and evening as the front works across. There is
considerable uncertainty in the exact timing of the front and
especially in the amount of instability that can build out ahead
of it. Both will play a critical role in the potential strength
of thunderstorms. The highly unstable solution from the NAM
(4000+ J/kg of MLCAPE) seems unlikely as it`s notably warmer at
the surface and cooler aloft than other camps. But a couple to a
few thousand Joules by the afternoon appear to be on the table.
Shear is marginal at best, but that sort of instability would
be supportive of potential severe weather with damaging winds
and marginally severe hail being the primary concerns. Would
like to think models should have a much better handle on the
pre-frontal environment by tomorrow. The convection should
largely be out of our area by the end of the evening.

On Saturday, the upper trough will strongly dig into the Great
Lakes region and quickly spin up a center of surface low
pressure to our east. It`s possible that a few widely scattered
showers develop on the backside of the system and fall on parts
of the area during the day on Saturday, although the day should
be largely dry with highs again forecast in the upper 70s to
near 80. High pressure will then meander about the region early
next week as seasonably warm conditions are favored to continue.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 602 PM CDT Wed Aug 19 2026

Showers and storms are expected south of the Chicago Metro
through midnight and thus, no weather hazards in the 00Z TAF.

Northeast winds around 10 knots are expected to prevail through
sunset before weakening. With clearing skies and light winds to
the northwest, there is a chance for localized BR or MIFG
around KRFD tomorrow morning, but dense fog is not expected and
confidence was too low for mention in the TAF. Winds will
return to around 10 knots out of the northeast tomorrow
afternoon before weakening and becoming easterly after
tomorrow`s sunset.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 1 AM CDT Thursday for ILZ032-ILZ033-ILZ039.

IN...Flood Watch until 1 AM CDT /2 AM EDT/ Thursday for INZ010-
     INZ011-INZ019.

LM...None.

&&

$$

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