747
FXUS63 KLOT 051722
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1222 PM CDT Wed Aug 5 2026

.KEY MESSAGES...

- A couple periods of showers and storms are expected in the
  general region through tonight. Repeated downpours may lead
  to localized flash flooding.

- Stormy conditions may return this weekend into early next
  week.

&&

.DISCUSSION...
Issued at 248 AM CDT Wed Aug 5 2026

Broad aggregate mid and upper-level troughing over the north
central CONUS will steer a few smaller scale impulses across our
area, resulting in a few clusters of showers and thunderstorms
across the region today into tonight. One such wave is currently
driving a line of heavy rain producing showers and storms
eastward across northern IL. Fortunately, the eastward movement
~25 mph is limiting the duration of heavy rainfall at any given
location, thus limiting the flash flood threat, at least in the
near term. Nevertheless, a quick localized inch of rain may fall
under the strongest cores.

Following this initial line of showers and storms, we will be
monitoring the trends with the ongoing cluster of storms over
IA. A good amount of available guidance suggests that this
activity will track eastward into northwestern IL around
daybreak. Thereafter, it remains a bit unclear as to how long it
may hold together as it moves into northeastern IL (especially
north of I-80) during the mid-morning hours, owing to the poor
diurnal timing and modest instability. Nevertheless, the current
thinking is that there will at least be a region of weakening
showers moving into the Chicago metro area (mainly in the 8-11
am timeframe). Should this activity hold together into
northeastern IL this morning, the presence of deep rich moisture
(precipitable water values nearly to 2") will support locally
heavy downpours.

After a break in the shower activity this afternoon, another
round of developing convection is probable near the surface
frontal boundary late this afternoon and evening in response to
the approach of the next mid-level impulse. However, with
diurnal destabilization expected to remain limited across far
northern IL (especially north of I-88 where temperatures will
stay in the 70s) as a result of persistent cloud cover through
the afternoon, the main focus for stronger convection will
likely end up south of I-80. This thinking continues to match
the SPC`s current Day 1 outlook, which indicates a level 1 of 5
severe threat into west central IL. The main threat with any
stronger storms would be locally strong damaging wind gusts and
locally heavy rainfall, particularly associated with any strong
storm clusters. The overall threat of flash flooding will
ultimately be dependent upon if and where multiple storms to
move over the same areas (training). While this possibility
cannot be ruled out on a localized basis in parts of our area,
the better potential for this may end up remaining south-
southwest of our area.

The focus for active weather should largely shift south of the
area for Thursday and Friday. However, active weather (with
shower and thunderstorm chances) is likely to return eighter
this weekend, or early next week.

KJB


Weekend onward:

As aggregate upper-level troughing shifts eastward toward the
end of the week, a quasi-zonal to northwesterly upper-level flow
pattern will materialize across the Upper Great Lakes region
supporting additional waves of showers and storms. Some of these
may be rambunctious as the eastern edge of an EML plume is
repeatedly re-advected eastward atop a stalled frontal boundary
draped across the Great Lakes. Naturally, confidence in
when/where eventual thunderstorm clusters will roam is low at
this range. With that said, the pattern matches conceptual
models for threats for severe weather and flash flooding in the
general region this weekend into early next week.

Borchardt/KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1222 PM CDT Wed Aug 5 2026

A frontal boundary is expected to stall over the airspace this
afternoon leading to periods of showers and worsening
visbys/cigs.

First off, a few thunderstorms may develop in the next few
hours directly over DPA/ORD/MDW/GYY as a lead wave interacts
with the warm and humid environment. Will cover this threat with
PROB30s with expectation for coverage to end up highest over
Lake Michigan. Later this afternoon, the area of showers and
storms over southern Iowa will slide eastward. Coverage of
thunder with the second round may be less owing to less
instability, though still expect at least -SHRA to move over all
but RFD favoring the 22-02Z time window. Forecast confidence
for thunder remains lower than average.

After sunset, showers may continue to fester along the stalled
frontal boundary across the area. So, will maintain the
inherited VCSH through the overnight hours. Calm winds and
abundant moisture should allow for cigs to build downward into
MVFR and IFR through the night especially away from Lake
Michigan. Areas of fog may develop as well. The inherited TAFs
handle such an idea well, though further adjustments downward
may be needed by the 00Z TAF set.

Improvement in cigs/visbys may be slow tomorrow morning though a
general trend upward is expected from mid-morning through early
afternoon seems reasonable. With the frontal boundary still in
the neighborhood, cannot rule out a shower or thunderstorm in
the airspace through the afternoon hours.

Borchardt

&&

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

&&

$$

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