163
FXUS63 KLOT 102352
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
652 PM CDT Mon Aug 10 2026

.KEY MESSAGES...

- Scattered thunderstorms this afternoon into this evening. Some
  thunderstorms may be severe with heavy rain and localized
  flooding.

- Possible line/complex of severe thunderstorms mid/late Tuesday
  morning into early Tuesday afternoon. Severe wind gusts to 80
  mph possible, along with heavy rain and localized flooding.

- Continued thunderstorm chances through the end of the week.

&&

.MESOSCALE...
Issued at 512 PM CDT Mon Aug 10 2026

We continue to see attempts at deeper/taller thunderstorms
stretching from the far northern Chicago suburbs to near the
Quad Cities. These storms have remained mostly elevated.
However, some of the storms are moving into a more favored
environment south of a diffuse bounday extending roughly along
the I-88 corridor.

South of the front and north of the Illinois/Kankakee River
valleys, modestly strong shear for mid-August will favor the
development of a hybrid between supercells and multicell
clusters with primarily damaging winds and isolated instances of
large hail. North of the boundary where shear is stronger,
elevated supercells will favor primarily large hail (especially
with left-splitting supercells) and some instances of damaging
winds. Overall coverage remains in question, favoring
isolated/scattered storms versus widespread storms.

The tornado risk remains non-zero, particularily during storm
interactions or with any supercells near the main boundary.
Lastly, some instances of flash flooding are possible if
multiple storms/clusters train over the same location this
evening. We will continue to assess the need for a Flash Flood
Watch, but current risk/coverage remains low enough at this
time.

Looking ahead, a mid-level wave currently over far southeast
South Dakota will track across southern Wisconsin and far
northern Illinois toward daybreak Tuesday coincident with
increasing shear and elevated instability. This may result in
elevated supercells with the primary risk of large hail over
northeast Illinois around daybreak. With this activity, the
flash flood threat is predicated on an existing low-level focus,
likely an outflow boundary from this evening`s storms.

Kluber

&&

.DISCUSSION...
Issued at 217 PM CDT Mon Aug 10 2026

The primary forecast challenge remains thunderstorm timing and
strength through midweek with a complex of severe thunderstorms
possible mid/late Tuesday morning into early Tuesday afternoon.

A very moist airmass is in place with dewpoints in the mid/upper
70s with a few locations tagging 80. Isolated thunderstorms have
persisted across eastern IA and far northwest IL the past few
hours but have been slow to strengthen. However, the expectation
is for this activity to continue moving east and to slowly
increase in coverage and intensity. As it taps into the high
instability in place, some of these storms may become severe
across northern IL and far northwest IN and persist through mid
evening. In addition to the severe threat, torrential rain and
localized flooding will also be possible though there remains
some uncertainty for how widespread any flooding may become.
Consideration was given for a flood watch but have opted to hold
off for now. Much of the guidance has trended drier for the
late evening and overnight hours tonight and have followed this
trend with this forecast though some showers and isolated
thunderstorms may linger.

Focus then shifts to a rather consistent feature in most of the
models for a complex of severe thunderstorms to develop over
northeast IA early Tuesday morning and race southeast across the
local area from mid morning Tuesday through early Tuesday
afternoon. Some of the cam solutions are quite concerning with a
line of severe thunderstorms moving across a large part of the
cwa. The updated SPC Day 2 outlook has included a level 3 of 5
severe threat for most of the area and given all of these trends
have mentioned wind gusts to 80 mph possible and if these storm
mature as shown on some of the cams, pockets of higher gusts
may materialize. Based on these trends, have also included
severe mention to the grids and zone forecast. Once these
storms exit to the east, there should be a lull in the
precipitation chances from mid/late Tuesday afternoon through
at least the early overnight hours Wednesday morning.

There is another wave that may move across the region
Wednesday morning with another potential severe thunderstorm
complex near or over the local area. Quite a bit of uncertainty
for this time period, but will need to be monitored closely. In
addition, all of these periods of heavy/torrential rain will
allow each following wave/complex to potentially produce
flooding more quickly and over larger areas.

The pattern is now looking quite active into this weekend,
though there remains quite a bit of uncertainty for timing and
location as a series of high pressure systems and cold fronts
move across the upper midwest and northern Great Lakes. How fast
these move, how far south they push, etc. will have large
impacts on when thunderstorms would be most likely across the
local area. cms

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 652 PM CDT Mon Aug 10 2026

Forecast concerns include...

Chance of thunderstorms this evening.
Possible line of severe thunderstorms mid/late Tuesday morning.
Possible mvfr cigs overnight/Tuesday morning.

Scattered showers and isolated thunderstorms will continue
through mid evening, as they move east across the area. There
may be additional thunderstorms later this evening into the
early overnight hours, but confidence is low. Lowered thunder to
prob mention for the Chicago terminals this evening and there
may be a gap with perhaps additional prob mention needed later
this evening and with later forecasts.

Primary forecast concern is the potential for a complex of
thunderstorms to move across the entire area mid/late Tuesday
morning through early Tuesday afternoon. Maintained previous
tempo timing for now, but latest guidance trends suggest thunder
may be just a little bit later and timing adjustments may be
needed with later forecasts. If this line of thunderstorms
materializes, gusts to 50 knots, possibly higher, will be
possible.

Patchy mvfr cigs are possible this evening then mvfr cigs will
be possible again Tuesday morning, but confidence is low and
maintained scattered mention. There may also be some light fog
and mvfr visibilities Tuesday morning given the very moist low
levels. cms

&&

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

&&

$$

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