536
FXUS63 KILX 300822
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
322 AM CDT Mon Sep 30 2024

.KEY MESSAGES...

- Patchy fog will develop along/east of a Champaign to Taylorville
  line tonight...with a low probability (20-40% chance) of
  visibilities dropping to less than one quarter of a mile in a
  few spots.

- A brief shot of cool air will spill into central Illinois behind
  a departing cold front on Tuesday. The coolest conditions will
  arrive Wednesday morning when low temperatures dip into the
  lower to middle 40s.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 322 AM CDT Mon Sep 30 2024

The cut-off upper low that has brought several days of clouds and
showers to the Ohio River Valley and parts of central Illinois
has shifted into eastern Kentucky early this morning and will
continue to gradually lift E/NE as the day progresses. Despite the
low moving further away, several CAMs continue to suggest isolated
mainly diurnally-driven showers along/south of I-70 this afternoon.
Have therefore continued the slight chance PoPs (20%) for that
area. Elsewhere, partly sunny and dry weather is expected. High
temperatures will range from the upper 70s near the Indiana border
to the lower 80s along/west of I-55.

A vigorous short-wave trough evident on 08z/3am water vapor
imagery over Alberta/Saskatchewan will track eastward over the
next 24 hours, pushing a cold front into the Midwest late tonight
into Tuesday morning. Clear skies and nearly calm winds ahead of
the front will set the stage for patchy fog tonight...especially
across the E/SE KILX CWA where clouds will be more prevalent today
and boundary layer moisture will be less prone to mixing out. Most
CAMs focus the lowest visibilities further east across Indiana:
however, the HRRR/RAP hint at patches of potentially dense fog as
far west as east-central Illinois. The 00z HREF shows a low
probability (20-40% chance) of visibilities dropping to less than
one quarter of a mile along/east of a Champaign to Taylorville
line. Will mention patchy fog across this area and keep an eye on
future model runs for visibility trends. Meanwhile further west,
the cold front will push into the Illinois River Valley after
midnight, bringing scattered clouds and increasing winds. Once
the front passes, a breezy and cooler day will be on tap for
Tuesday. NW winds will gust 20-30mph and high temperatures will
drop into the lower 70s along/west of I-55.

Barnes

.LONG TERM...(Wednesday through Sunday)
Issued at 322 AM CDT Mon Sep 30 2024

High pressure will build into Illinois Tuesday night, resulting in
clear skies and nearly calm winds. This will allow excellent
radiational cooling of the dry airmass and create chilly lows in
the lower to middle 40s. The 00z LREF even shows a very low
probability (10-15%) of temperatures dropping below 40 degrees
along/north of a Macomb to Peoria line. The high will remain
overhead on Wednesday, leading to a sunny day with highs in the
lower 70s.

Once the high shifts off to the east and SW boundary layer flow
resumes, temperatures will bounce back into the upper 70s and
lower 80s by Thursday/Friday. After that, another short-wave
trough will skirt across the Northern Plains into the Great Lakes
within the west-to-east zonal flow pattern by the end of the week.
This will push a weak cold front through late Friday and drop
readings back into the lower to middle 70s by Saturday. No
precipitation is expected in the extended forecast.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1130 PM CDT Sun Sep 29 2024

Skies have mostly cleared across the terminals late this evening,
but cloud cover continues to stream southwest out of Indiana.
Upstream obs are showing MVFR ceilings across central Indiana,
and new HREF guidance continues to show this advecting into
Illinois, reaching KCMI toward 09-10Z and KBMI/KDEC toward 12Z.
Highest probabilities (60-70%) of sub-1000 foot ceilings remain
focused in the KBMI-KCMI corridor, for a few hours between 11-15Z.
While conditions improve over most of central Illinois around mid
morning or so, the MVFR conditions at KCMI are likely to continue
into mid afternoon.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$