191 
FXUS63 KILX 041934
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
234 PM CDT Thu Sep 4 2025

.KEY MESSAGES...

- Smoke from wildfires west of the Rockies will spill overhead
  tonight...creating a hazy overcast. Low-level air quality will
  not be significantly impacted.

- Below normal temperatures in the 60s and 70s will prevail
  through next Monday before readings climb back above normal into
  the middle to perhaps upper 80s by the middle and end of next 
  week. 

&&

.SHORT TERM...(Tonight through Friday)
Issued at 234 PM CDT Thu Sep 4 2025

19z/2pm visible satellite imagery shows a thick plume of smoke 
across Nebraska/Kansas. While surface visibilities have occasionally
been reduced to 5-6 miles along the leading edge of the smoke across
far western Iowa/Missouri, it appears the majority of the smoke is
elevated. The HRRR near-surface smoke density is currently
maximized where visbys are reduced, but the density tends to
decrease as the smoke shifts eastward and pushes into the Illinois
River Valley this evening. Meanwhile vertically integrated smoke
values are significantly higher and remain high as they spread
across all of central and southeast Illinois tonight. Given upstream
obs and the consistent signal from the HRRR, think the main impact
from the smoke will be a hazy overcast...with little to no air 
quality issues at ground level. Have added patchy smoke to the 
forecast across the Illinois River Valley where near-surface 
values are highest and have increased sky cover everywhere 
accordingly.

Low pressure tracking eastward out of the Dakotas across the Upper
Midwest will pull a cold front southward into Illinois late
tonight. The strongest forcing with this feature will remain
further north closer to the low track and deep-layer moisture will
be completely lacking. Am therefore expecting a mostly dry
forecast, with perhaps a few light sprinkles north of a Macomb to
Lacon line around midnight.  

Once the front passes, northwesterly winds throughout the depth of
the atmosphere will push the elevated smoke out of the area by
midday Friday. Meanwhile, frontogenetic forcing north of the
surface boundary will result in overcast conditions with one or
more bands of light rain showers. The forcing is strongest within
the 700-500mb layer from Macomb eastward to Bloomington during the
morning...then shifts southward and weakens by afternoon. While
forecast soundings show a dry boundary layer, think the strong
forcing aloft will be enough to squeeze out a few showers and a
couple hundredths of an inch of rainfall. Most CAMs focus very
light showers north of I-72 and west of I-55 Friday morning...then
further E/SE across the remainder of the area during the
afternoon. Models have been consistently showing renewed
frontogenetic forcing Friday night...primarily along/south of I-70
where chance PoPs will linger through the night. Will need to keep
a close eye on future model runs, as PoPs may need to be spread
further northward to the I-72 corridor depending on the
strength/track of the upper-level forcing.

Barnes

.LONG TERM...(Saturday through Thursday)
Issued at 234 PM CDT Thu Sep 4 2025

Once the surface front drops well south of the Ohio River and high
pressure builds in from the north, an extended period of cool and
dry weather will be on tap this weekend. High temperatures on
Saturday and Sunday will only reach the lower to middle 70s while
overnight lows dip into the lower to middle 40s. The atmosphere
will gradually modify...with highs slowly climbing back into the
upper 70s and lower 80s by Tuesday. After that, medium range
models show upper heights rising sharply...with a significant
upper ridge building over the Tennessee/Ohio River Valleys. This 
will lead to a return to more summer-like readings in the middle 
to upper 80s by the middle and end of next week. 

Barnes

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1247 PM CDT Thu Sep 4 2025

VFR conditions will prevail through the entire 18z TAF period. A
band of SCT-BKN diurnal Cu at around 4000ft will traverse the area
from west to east through mid-afternoon before dissipating and/or
exiting into Indiana after 21z. While the sky will be cloud-free
early this evening, an upper-level smoke plume currently west of
the Mississippi River will spill eastward...creating a milky
overcast through the night. Winds will initially be W/NW at around
10kt, then will back to S/SW toward sunset. As a cold front
approaches from the west, S/SW winds will increase and become
gusty from late evening until FROPA...at which times the winds
will veer back to NW. Latest forecast soundings and numeric
guidance suggest NW gusts of 15-20kt with a few spots potentially
climbing to near 25kt at times behind the departing cold front
Friday morning. In addition to the winds, the CAMs are in general
agreement that a thick band of mid-level cloudiness at around
10,000ft will develop across the TAF sites after 11z. While the
boundary layer will remain dry, think there will be enough forcing
aloft to create one or more bands of very light rain showers.
Based on the general placement of those bands as seen by the 12z
HRRR/NAM, have included predominant showers at both KPIA and
KBMI...with just VCSH at the I-72 terminals.

Barnes

&&

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

$$