NWS Chicago Decision Support Briefing - Forecast

796
FXUS63 KLOT 161833
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
133 PM CDT Fri Oct 16 2026

.KEY MESSAGES...

- Breezy and seasonably chilly conditions persist this
afternoon with some scattered showers.

- East of Gary, lake enhanced showers this afternoon will
transition to lake effect showers tonight with a slight chance
of a thunderstorm near the shore late this afternoon/early
this evening. Wind gusts to 45 mph possible near the northwest
Indiana lakefront this afternoon/early evening.

- Coldest night of the season expected tonight with lows
near/just below freezing across interior portions of northern
IL.

- Dry and mild weather returns Sunday and persists next week.

&&

.DISCUSSION...
Issued at 133 PM CDT Fri Oct 16 2026

A seasonably strong and expansive high-pressure system over the
Great Plains continues to build eastward into the Midwest this
afternoon, following a surface low moving into New England.
Strong northerly winds between these systems are pushing the
season`s coldest airmass southward into the area, resulting in a
cloudy, chilly, and breezy day across the region. A few widely
scattered showers remain possible across northern Illinois
through sunset as an upper-level trough moves overhead. However,
shower activity will primarily concentrate over Lake Michigan
late this afternoon and evening as lake-effect parameters
rapidly improve. This should lead to focused lake-effect
showersand potentially a few thunderstormsshifting inland from
southern Lake Michigan into northwestern Indiana this evening.
Scattered lake effect showers may linger after midnight, but
they are expected to diminish toward Saturday morning as
inversion heights lower and lake-effect parameters weaken
following the passage of the upper-level trough.

Outside of lake-effect precipitation and cloud cover in
northwestern Indiana, skies will clear and winds will gradually
subside this evening. This will be especially true across
interior portions of northern Illinois, where the coldest
temperatures of the season are forecast tonight. The current
forecast remains on track for a couple of hours of near-freezing
temperatures early Saturday morning, most notably across far
northern Illinois from the Fox Valley westward. Consequently, no
changes were made to the frost and freeze headlines in effect
for interior northern Illinois late tonight.

Following a chilly and frosty start on Saturday, full sunshine
and light winds are forecast as the surface high moves directly
over the region. The abundant sunshine will help temperatures
rebound into the upper 50s during the afternoon. Another chilly
night will follow Saturday night as temperatures drop back into
the 30s. Given the light winds, additional frosty conditions are
possible, particularly east of I-55 where the lightest winds
are expected. We will continue to monitor this period for
potential frost headlines.

The cold snap will be short-lived as conditions transition back
to a mild and dry autumn pattern. High temperatures are
forecast to return to the 60s on Sunday and Monday, before
warming into the 70s for the remainder of next week with little
to no chance of rain.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1234 PM CDT Fri Oct 16 2026

Key concerns for the 18Z TAF period:

* Scattered light showers this afternoon

* MVFR cigs over Chicagoland returning to VFR this afternoon

* At GYY, periods of lake-effect rain expected late this
afternoon and again late tonight into early Saturday

Scattered coverage of light rain is dropping into northern IL
from the north early this afternoon. Periods of light rain will
be possible through the rest of the afternoon. MVFR cigs over
the region have recently scattered out over RFD with more VFR
found upstream. Chicagoland sites are expected to return to VFR
by mid- afternoon.

At GYY, a band of lake-effect rain showers will target far
northwest IN late this afternoon into early evening. Periods of
light to moderate rain with MVFR vsby reductions are
anticipated. A second push is expected after midnight and may
last into early Saturday.

Meanwhile, NW winds will trend toward NNW through the afternoon
while regular gusts are expected to get up to near 30 kt for
the middle and late afternoon. NNW winds will remain gusty
through much of the night before easing for Saturday.

Doom

&&

.MARINE...
Issued at 133 PM CDT Fri Oct 16 2026

Northerly gales to 40kt are forecast this afternoon and evening,
with strongest gusts to 40kt+ likely within the lake enhanced
convergence band and with more robust lake effect showers over
the Indiana waters east of Gary. In addition to an isolated
thunderstorm or two late this afternoon, conditions are expected
to become favorable for waterspouts late this afternoon into
this evening. Waterspout risk is expected to diminish late this
evening as inversion heights lower. Lake effect shower intensity
and coverage will decrease overnight also in response to the
decreasing inversion heights.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Freeze Warning from 5 AM to 8 AM CDT Saturday for ILZ003-
ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012.

Frost Advisory from 5 AM to 8 AM CDT Saturday for ILZ006-
ILZ019-ILZ020.

IN...Wind Advisory until 10 PM CDT this evening for INZ002.

LM...Gale Warning until 1 AM CDT Saturday for the IL and IN
nearshore waters.

&&

$$

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