440
FXUS63 KLOT 140103
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
803 PM CDT Mon Oct 13 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 /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 646 PM CDT Mon Oct 13 2025

Key Messages:

- Potential for MVFR or lower ceilings overnight into tomorrow
  morning.


Light northerly winds are expected tonight before gradually
veering more northeasterly and increasing to around 10 kts after
sunrise tomorrow. With low-level flow expected to retain a
similar direction, a lake-induced stratus deck will spill inland
and affect the terminals overnight into tomorrow morning. At
least intermittent MVFR ceilings appear likely to be observed
during this time before prevailing VFR conditions return later
on in the day.

In addition, a relatively small patch of LIFR/IFR ceilings
exists in southeastern Wisconsin at press time. These clouds are
likely to drift southward into northern Illinois tonight and
may further be augmented by the continuous feed of low-level
moisture oozing inland from Lake Michigan, which some forecast
guidance has recently become increasingly bullish about.
Confidence is thus increasing that one or more of our TAF sites
may see a period of IFR or lower ceilings overnight into early
tomorrow morning. For starters with the 00Z TAF package, opted
to introduce a TEMPO group with some SCT lower clouds during the
overnight hours in the Chicago metro TAFs. However, if the
recent trends in guidance hold for a few more model cycles and
observational trends continue to support this more pessimistic
scenario, then IFR or LIFR ceilings will likely need to be
introduced formally into some or all of our TAFs with the 03Z
AMDs or the 06Z TAF package.

Ogorek

&&

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

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

&&

$$

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