748
FXUS63 KLOT 282340
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
640 PM CDT Wed Oct 28 2026

.KEY MESSAGES...

- A cold front will move across the area tomorrow accompanied by
  isolated to scattered showers (20-40% chance at any given
  spot). A lightning strike cannot be ruled out (10-15% chance).

- Periods of showers and a few storms are favored Friday night
  through early Saturday afternoon (>60% chance areawide).
  Coverage of showers may taper in time for outdoor Halloween
  activities.

- Generally mild conditions will continue into the first week of
  November before a pattern change leads to more showery and
  cooler conditions by the first weekend of the month.

&&

.DISCUSSION...
Issued at 133 PM CDT Wed Oct 28 2026

Early afternoon water vapor imagery reveals a vigorous upper-
level short-wavelength trough propagating northeastward across
Minnesota toward Lake Superior. A parent surface low is located
in western Ontario with secondary surface low development
underway near the Twin Cities along a trailing cold front. A
plume of modestly steep mid-level lapse rates (sampled near 7.5
K/km per the 18Z DVN RAOB) extends ahead of the front across
the middle Mississippi River Valley. Meanwhile, closer to home,
it is another beautiful late October day with temperatures in
the mid 70s, mostly sunny skies, and a southwesterly breeze.

This afternoon and evening, coverage of showers and
thunderstorms will increase from central Iowa into central
Minnesota as the secondary low deepens and cold front shifts
southeastward. Isentropic ascent ahead of the front will
encourage a few showers or storms to develop as far southeast as
northern Illinois after sunset and through the overnight hours,
though a resident dry low-level airmass should render coverage
isolated at best (20 to 30% chance, especially north of I-80).
Overnight lows will be unusually mild for the time of year and
in the mid to upper 50s.

The cold front is expected to cross southward into Illinois
after sunrise accompanied by a band of low to mid-level clouds.
Suppose a few showers may accompany the front north of I-88
during the morning hours though minimal instability suggests
otherwise. With that said, can easily envision renewed shower
development (diurnally-driven) along the front by mid-afternoon
somewhere near the I-88 or I-80 corridors (30 to 50% chance).
Forecast soundings do not look particularly impressive from a
thermodynamic perspective, but will tuck in an isolated thunder
chance (10-15%) just to be safe as the front progresses
southeastward through the afternoon. Temperatures tomorrow will
be somewhat regulated by the position of the frontal boundary
with highs in the lower 70s near US-24 to generally the low to
mid 60s elsewhere.

A surface high pressure system will quickly build into the
region Thursday evening setting the stage for ideal conditions
for radiational cooling (slackening winds, clearing skies, dry
airmass). Will undercut NBM guidance and feature overnight lows
generally in the upper 30s to lower 40s, but will forgo mention
of frost for now (would be near the Wisconsin state line should
it occur). A relatively cool start to the day, increasing mid-
level cloud cover, and easterly flow off Lake Michigan will hold
temperatures on Friday to the lower 60s north of I-80 to around
70 near US-24.

Attention then turns toward a conglomerated upper-level wave
emanating from northern Mexico due to arrive to the Lower Great
Lakes this weekend. Am noting a trend toward stronger isentropic
ascent ahead of the wave Friday night which would support a
healthy coverage of showers and storms from eastern Iowa into
northern Illinois, though will note quite a bit of guidance that
isn`t as excited. Nevertheless, do anticipate at least
scattered activity moving through the area through Saturday
morning with a signal for gradually waning coverage through the
afternoon hours (hopefully in time for outdoor Halloween
activities). Temperatures should cool toward the lower 50s after
sunset.

Looking toward next week, ensemble model guidance depicts a
storm system or two moving through the central CONUS followed by
a pattern change toward more showery and cooler conditions.

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 640 PM CDT Wed Oct 28 2026

Forecast concerns include...

Chance of showers tonight through midday Thursday.
Mvfr cigs Thursday morning.
Low level wind shear overnight.
Wind shift to northwest with a cold front Thursday morning.

Some sprinkles and isolated showers will be possible across
northwest IL this evening but there will be a better chance of
showers overnight through midday Thursday as a cold front moves
across the area. Current prob mention has this potential handled
well. There may be a gap between a period of showers across
northern IL in the morning and then new development of showers
mainly south of the terminals midday into Thursday afternoon.
There is also the potential for a few isolated thunderstorms,
but confidence for thunder is too low for any mention with this
forecast.

South/southwest winds around 10kt will continue this evening,
with a few higher gusts at times. Directions will turn more
southwest toward daybreak, then shift to the northwest as the
cold front moves across the area Thursday. Low level winds will
steadily increase this evening with low level wind shear
expected overnight and through daybreak Thursday morning.

A period of mvfr cigs is expected mainly from daybreak through
late morning associated with the cold front. The mvfr cigs may
become prevailing for at least a few hours before scattering out
by early/mid Thursday afternoon. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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