024
FXUS63 KLOT 190552
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1252 AM CDT Wed Aug 19 2026

.KEY MESSAGES...

- Scattered thunderstorms are possible this evening (50%
  chance), some of which may be capable of damaging wind gusts
  and heavy downpours which may lead to localized flooding.

&&

.DISCUSSION...
Issued at 130 PM CDT Tue Aug 18 2026

An area of showers, with a few embedded storms, have been
developing across parts of northwestern IL and far southern WI
over the past couple hours. It appears this activity is tied to
a corridor of warm air advection just in advance of a remnant
MCV shifting into northeastern IA. We anticipate this isolated
to widely scattered activity to shift eastward across far
northern IL (mainly north of I-80) this afternoon well in
advance of an approaching cold front over the Upper Midwest.
Lightning activity is expected to remain isolated, and likely
focused closer to the WI state line the next few hours as the
instability gradient begins to slide southeast. We do not
anticipate much of a severe threat with these initial showers
and storms this afternoon.

The cold front currently extends from southeastern MN east-
northeastward into northeastern WI. Additional strong to severe
thunderstorms are expected to develop near the front late this
afternoon as the prefrontal airmass moistens/destabilizes.
Deep-layer shear will support organized severe weather, driven
by 45-50 kt mid-level westerly flow overspreading the warm
sector at the base of a digging mid-level trough. Initial
supercells along the front are expected to upscale into a
southeastward-propagating clusters into southern/southeastern
WI late this afternoon, potentially reaching northern IL this
evening. The primary local threats include torrential rainfall,
frequent lightning, and damaging wind gusts exceeding 60 mph.
While the highest threat is currently near the WI state line,
localized damaging winds may persist across the Chicago metro
area this evening, roughly between 7 and 11 PM.

On Wednesday, the primary threat for convection shifts toward
central IL and IN, well south of I-80. However, lingering low-
level moisture in northeastern IL may support isolated afternoon
showers and storms, particularly along the lake breeze
boundary. No severe weather is expected Wednesday afternoon, and
most areas should remain dry. Given recent trends, a 20% chance
of afternoon storms has been included for northeastern IL. High
temperatures will reach the low 80s inland and mid-70s along
the lakeshore.

Surface high pressure will move overhead Thursday, bringing
light winds, mostly sunny skies, and lower humidity.
Temperatures in the upper 70s to near 80 will make for a
pleasant day. Forecast confidence decreases late in the week as
additional waves move through the northwest flow pattern,
bringing a return of shower and storm chances on Friday. While
some storm threat could linger into Saturday, Sunday currently
looks dry with pleasant temperatures in the 70s.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1252 AM CDT Wed Aug 19 2026

A weak and diffuse cold front currently over central Wisconsin
will drift southward across northern Illinois this afternoon.
Meanwhile, high pressure will drift eastward toward the western
Great Lakes. The combination of these two features will result
in a gradual veering of the winds (at around 5 knots or less)
from W early this morning, NNW by daybreak and NNE by mid-
morning. A lake-enhanced wind shift will then allow winds to
settle NE early this afternoon and through the remainder of the
period, with speeds 10 to 15 knots at times this afternoon.

Light/calm winds, passing mid/upper-level clouds, and plenty of
surface-layer moisture will allow fog and/or LIFR stratus to
develop across interior northern Illinois early this morning
through sunrise. Have included TEMPO LIFR visibility at RFD and
IFR visibility at DPA from 10-14Z, though both sites could see
VLIFR visibility. Have also include VFR BR at ORD/MDW during the
same window, with a low chance (under 30%) that fog well
northwest of the core of the Chicago metro drifts toward ORD/MDW
as IFR stratus around daybreak.

With the abundant low-level moisture in place ahead of the cold
front, diurnal mixing should yield a period of MVFR ceilings at
all sites mid to late morning. Stratocumulus will then lift
into VFR levels and scatter through the afternoon, with drier
and nearly SKC conditions tonight.

Kluber

&&

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

&&

$$

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