915
FXUS63 KLOT 140531
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1231 AM CDT Tue Oct 14 2025

.KEY MESSAGES...

- A chance (30-50%) for showers Tuesday night, north of I-80.

- A more active weather pattern looks will bring increasing rain
  chances (35-55%) next weekend.

&&

.UPDATE...
Issued at 803 PM CDT Mon Oct 13 2025

Minor adjustments made to the forecast this evening, primarily
to increase cloud cover farther southeast across the forecast
area. Also raised min temps a bit where clouds are expected to
persist, and added a mention of some patchy fog toward the IL/WI
border.

Early evening surface analysis depicts a weak cold front
drifting very slowly to the east across the IL portion of the
forecast area. With primary short wave forcing and it`s
associated surface low pressure center well north of the region,
the cold front is expected to wash out across the area overnight,
leaving an axis of increased low-level moisture and light north
to northeast winds across the area into Tuesday. While spotty
sprinkles and light showers earlier today have dissipated with
the loss of mid/upper level forcing, the lingering low-level
moisture axis has resulted in persistent cloud cover across much
of the forecast area which appears will stick around at least
into Tuesday morning. Areas along the IL/WI border northwest of
the decaying front have a little better potential to see clouds
scatter, though moist low-levels and light northeast winds
suggest that low stratus and patchy fog may fill back in across
these areas by morning.

Given these trends, have beefed up cloud cover southeast of
I-55, raised overnight lows slightly across our central cwa where
cloud cover looks to be more persistent, and added a mention of
patchy after midnight into early Tuesday north/northwest of
Chicago.

Ratzer

&&

.DISCUSSION...
Issued at 152 PM CDT Mon Oct 13 2025

Through Tuesday Night:

Light showers/sprinkles have now largely dissipated across
northern IL as they move east. This is due to forcing from a
northern stream upper trough shifting away, along with a
strengthening upper ridge extending from the southern Plains and
into the lower Great Lakes. Skies are mostly cloudy, and will
continue to fill in for areas where cloud breaks have allowed
temperatures to reach into the 70s.

A cold front across northwest IL and into WI will slowly move across
the area tonight and will shift winds to the northeast. This
front will bring cloudy skies but it will remain dry. High
pressure behind the front will maintain onshore flow through
Wednesday and will create for a larger temperature gradient
across the area with 70s well inland and 60s for areas closer to
the lake. The upper ridge will hold on Tuesday and maintain dry
conditions during the day and into the evening hours.

The next disturbance of interest is working its way in southwest
flow ahead of the deep trough in the west. Precipitation chances
increase later Tuesday night into early Wednesday as this
disturbance crests the upper ridge. There are some signals that
we will get some initial erosion of precipitation similar to
what has been occurring today. The highest chances appear to be
north of I-80 with perhaps some potential for any precip that
develops to be north into southern WI.

KMD

Wednesday through Monday:

Lingering shower activity across far northern Illinois (north of I-
80) will diminish late Wednesday morning or early afternoon, as
a ridge of high pressure helps to dry out the lower atmosphere.
Surface high pressure associated with this upper level system
will drop into the mid-Atlantic states from the northern Great
Lakes, allowing a strengthening low pressure system in the
Rockies to eject northeast through the upper Plains during the
second half of the week. These systems are modeled to begin
lifting moisture back into the mid and upper Mississippi River
Valley`s during the second half of the week into next weekend.

As the warm nose lifts through the upper Mississippi River Valley
Thursday morning, limited chances of precip (<20%) will be possible
across northwest IL, as the high pressure side remains in control.
Heading across the border in Wisconsin, chances of precipitation
increase the further north throughout Thursday. High pressure then
streams south along the Atlantic coast to end the week,
ushering slightly warmer temperatures (mid to upper 70s
areawide) and additional moisture into the Midwest and Ohio
River Valley. Some uncertainty exists with the overall coverage
of precipitation throughout the weekend; with some camps having
a frontal push and ending rain Saturday, while others have
chances of precip throughout much of the weekend. NBM remains
with the main frontal push Saturday which brings the majority of
widespread chances, before leaning on the ECMWF for lingering
activity further southwest on Sunday. Looking at some
probabilistic NBM 24-hour precip data: trends are at a 30-50%
exceedance of 0.5-inch north of I-80, while trending closer to
50% exceedance of 0.5-inch south of I-80. So while this system
does not appear to be a soaker at this time for our area, we
will continue to monitor trends over the next several days.

Seasonal temps will linger through mid-week climb and back
above normal to end the week, before a cool down back to
seasonal after the weekend system exits.

Baker/KMD

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1231 AM CDT Tue Oct 14 2025

Forecast concerns include...

Possible fog early this morning.
Mvfr cigs, possible ifr cigs this morning.
Chance of showers Wednesday morning.

A weak cold front is moving south across the area currently with
fog across southeast WI. Some of this fog will likely spread
into far northern IL early this morning though there remains
uncertainty for how widespread it will become. Current guidance
suggests the best chance for fog will remain northwest of the
Chicago terminals and for now, have only included mention at
RFD/DPA.

Guidance also suggests that mvfr cigs will develop over the next
several hours and persist through late morning/early afternoon
before lifting and possibly scattering out. There is some
potential for brief or pockets of ifr cigs. Confidence is low
for specific cig heights and opted to maintain mvfr cigs for all
locations, though did include a tempo ifr cig at RFD with the
potential for fog there.

Light northerly winds will turn to the north/northeast overnight
with speeds increasing to 10kt by daybreak which will continue
today, perhaps in the 10-12kt range. Winds look to increase some
early Wednesday morning, when gusts into the 15-20kt range are
possible, especially for the Chicago terminals.

There will be a chance of showers Wednesday morning with the
best chances for the Chicago area likely centered around
daybreak Wednesday morning with the overall duration possibly
just a few hours at any one location. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM this morning to 7 AM CDT
     Wednesday for Winthrop Harbor to Wilmette Harbor IL.

     Small Craft Advisory from 1 PM this afternoon to 7 AM CDT
     Wednesday for Wilmette Harbor to Calumet Harbor IL.

&&

$$

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