NWS Chicago Decision Support Briefing - Forecast

101
FXUS63 KLOT 011854
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
154 PM CDT Fri Aug 1 2025

.KEY MESSAGES...

- Wildfire smoke will continue to cast a milky look to the sky
for the foreseeable future.

- Pleasant weather characterized by seasonably cool temperatures
and low humidity levels will prevail through early next week.

&&

.DISCUSSION...
Issued at 140 PM CDT Fri Aug 1 2025

Through Saturday:

A surface high pressure system centered over the Great Lakes
will serve as the primary influence on our weather tonight and
tomorrow. Incoming upper-level cloud cover will limit otherwise
ideal conditions for radiational cooling tonight (light winds,
low humidity levels). Overnight lows will range from the lower
50s in outlying areas to the lower 60s lakeside. Tomorrow looks
similar to today with an east-northeasterly breeze and highs in
the mid to locally upper 70s. Upper-level smoke will continue to
provide a murky look to the sky for the foreseeable future.

Borchardt


Saturday Night through Friday:

High pressure centered across Wisconsin and Lower Michigan on
Sunday will drift eastward to the Canadian maritime provinces
through the middle of next week. The broader mid-level flow
across the CONUS will remain more-or-less blocked with a 600dam
500 hPa ridge over the southwest states and a weaker ridge
crossing southern Canada. Between these ridges and the surface
high to the east, a mid-level trough over the central California
coast will round the southwest ridge into the central CONUS on
Monday before becoming increasingly sheared across our area
Tuesday into Wednesday. Atlantic-based moisture will be drawn
NNW toward the lower Ohio and mid-Mississippi River Valleys by
Monday and especially Tuesday. This would ultimately support
isolated to widely scattered diurnally-driven thunderstorms as
close as central Illinois Monday afternoon and over the entire
forecast area on Tuesday and possibly into Wednesday. A majority
of the forecast area should remain dry during this period,
though will continue to advertise higher chances on Tuesday. A
broad trough crossing the far northern Great Lakes late in the
week will erode a low-amplitude ridge nosing northeastward into
the southern Great Lakes, supporting the potential for an MCS
episode somewhere across the western Great Lakes during this
time.

Kluber

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1224 PM CDT Fri Aug 1 2025

There are no aviation concerns through the TAF period.
Northeasterly winds will prevail this afternoon before becoming
light and variable overnight. After daybreak tomorrow, winds
will become east northeasterly once again. Occasional bouts of
largely VFR clouds will prevail. Haze due to wildfire smoke
should continue to increase through the afternoon, though
trapped smoke aloft will maintain a milky look to the sky.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Air Quality Alert until midnight CDT tonight for ILZ003-ILZ004-
ILZ008-ILZ010-ILZ011-ILZ019-ILZ023-ILZ032-ILZ033-ILZ039.

Air Quality Alert until midnight CDT Saturday night for ILZ005-
ILZ006-ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-
ILZ106-ILZ107-ILZ108.

Beach Hazards Statement until 4 PM CDT this afternoon for
ILZ103-ILZ104.

IN...Air Quality Alert until midnight CDT Saturday night for INZ001-
INZ002-INZ010-INZ011.

Beach Hazards Statement until 4 PM CDT this afternoon for
INZ001-INZ002.

LM...None.

&&

$$

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