876
FXUS63 KLOT 300716
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
216 AM CDT Mon Sep 30 2024

.KEY MESSAGES...

- Chilly Tuesday night into Wednesday morning, otherwise near or
  above normal temperatures are favored through the week. Dry
  conditions also expected outside of a <20% chance of a few
  showers or storms late Thursday night.

&&

.DISCUSSION...
Issued at 216 AM CDT Mon Sep 30 2024

Through Tuesday:

While skies remain mostly clear across far northern IL
(especially to the north of I-88), a broken deck of stratus
continues to stream westward into the area along the far
northwestern periphery of a weakening area of low pressure over KY
and TN. The cloud cover is likely to keep the threat of fog
rather low for most areas. The main area we will have to keep an
eye on for any patchy early morning fog is those areas near the
WI state line in far northern IL where cloud cover is expected to
remain sparse during the predawn hours.

The weakening KY/TN low will continue to weakening today as it
slowly begins to slide to the east. As it does so, we should see
more sunshine today, though some increased cloud cover may linger
across my southeastern counties for a few hours today. Otherwise,
some developing shallow diurnal fair weather cu should make for a
partly cloudy afternoon for most areas. Temperatures will be
warmer today, with readings likely to top out in the lower 80s
across interior portions of northern IL. However, closer to the
lake and into northwestern readings are expected to be a bit
cooler, generally in the mid to upper 70s.

A cold front, associated with a strong storm system tracking
northeastward from the Prairie Providences of Canada into the
Hudson Bay today on Tuesday, will shift southeastward across the
area early Tuesday morning. Chances for precipitation with the
frontal passage continue to be low (<20%), so it is unlikely that
anything more than a brief light shower would materialize early
Tuesday morning. Winds will become gusty (25 to 30 mph) for a
period in the wake of the frontal passage Tuesday morning, but
speeds look to ease through the afternoon as a large surface high
beings to quickly build over the Midwest.

A cooler, and much drier, airmass will shift in over the area on
these northwest winds Tuesday. This will foster rather low
afternoon relative humidity values (25 to 35 percent) across
interior sections of northern IL. This does cause some concern
for the threat of wildfire spread across northwestern parts of IL,
especially since winds do look to remain in the 10-20 mph range
for a few hours in the afternoon. In spite of this, it appears
unlikely conditions will reach a critical level to warrant a Red
Flag Warning.

KJB


Tuesday Night through Sunday:

A dry and seasonably cool airmass will briefly advect across
the area behind Tuesday`s cold front. With an associated surface
ridge crossing the forecast area at a favorable time late
Tuesday night, a chilly night is expected away from the core of
the Chicago metro. Upper 30s are appearing more likely in the
outlying areas of northern Illinois, with some mid 30s readings
not out of the question in the typically coldest locales. Dry
conditions will persist through Thursday amid mostly clear skies
as highs in the low 70s Wednesday warm to around 80 for
Thursday.

A broad longwave trough crossing southern Canada and the
northern Great Plains Thursday into Friday will induce a weak
surface trough/cold front across the Upper Mississippi River
Valley. This front will cross the forecast area late Thursday
night into Friday night. The combination of a very dry
antecedent airmass and poor moisture transport from the
southwest (flow in the northern Gulf of Mexico will be E or NE
owing to a tropical disturbance in the bay of Campeche) will
favor a dry frontal passage. Have only some slight chance PoPs
across northern Illinois late Thursday night as enough ensemble
members still imply at least sparse coverage of showers or
convection.

Expansive high pressure will settle over the region later
Friday through Saturday ahead of another moisture-starved
northern trough nearing the area Sunday into next Monday.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1236 AM CDT Mon Sep 30 2024

BKN/OVC VFR stratus is expected to diminish in coverage to SCT
through the early morning hours, then persist through the
remainder of the period. Where clearing occurs early this
morning, radiational cooling will likely result in some MVFR BR
and/or BCFG at DPA/GYY and especially RFD. Will also need to
monitor the potential for shallow IFR stratus to develop in
southeast WI over the next few hours that could advect toward
RFD closer to daybreak.

NE winds around 5 knots or less will gradually veer ESE 5-10
knots this afternoon, then continue veering SW this evening. A
cold front will be either approaching or reaching the Chicago
terminals at the end of the ORD/MDW forecast period (12Z
Tuesday). Winds with this front will abruptly shift NNW with
gusts around or briefly higher than 25 knots.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 7 AM CDT this morning for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement until 7 AM CDT this morning for INZ001.

     Beach Hazards Statement until 4 AM CDT early this morning for
     INZ002.

LM...Small Craft Advisory until 4 AM CDT early this morning for the
     IL and IN nearshore waters.

&&

$$

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