912
FXUS63 KILX 020435
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1135 PM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Rain chances return this week. There is currently a high
  (60-80%) chance Wednesday afternoon/evening, and then a very low
  (10-20%) chance Friday morning/afternoon. Severe weather is not
  anticipated at this time.

- Unusually cool temperatures arrive by Thursday with afternoon
  highs struggling to breach 70 F.

&&

.DISCUSSION...
Issued at 230 PM CDT Mon Sep 1 2025

The stretch of dry, mild, and otherwise low-impact weather will
continue through Tuesday as an atmospheric blocking pattern and its
associated surface high pressure remain anchored over the eastern
half of the US. Recent water vapor imagery depicts a compact mid-
level shortwave trough meandering across the Missouri Valley this
afternoon, and model guidance is in excellent agreement that this
disturbance will stay just off to our south as it becomes enveloped
by the main belt of westerlies and digs toward the Tennessee Valley
overnight. Amid the dry conditions, afternoon temperatures for both
today and Tuesday will warm into the lower 80s, with overnight lows
in the middle 50s.

An abrupt pattern change will then take shape by Wednesday as the
polar jet stream buckles over the northern U.S. and sends a
strong shortwave trough and its attendant cold front southward
into the Great Lakes. Breezy south winds (20-25 mph) ahead of the
cold front will help boost temperatures into the mid 80s by
Wednesday afternoon. Moisture-return ahead of the front will be
hampered by troughing over the Gulf coast, with only a narrow
tongue of low 60s dewpoints expected to surge in ahead of it
Wednesday afternoon. This will limit both convective chances
(20-40%) and QPF (0.2"-0.4") alike. Nevertheless, we are calling
for likely (60-80%) rain chances Wednesday afternoon/evening.
Despite increasing wind shear (25-35 kts), severe weather chances
remain quite low due to meager instability (< 500 J/Kg MLCAPE).

The bigger weather story will be the sharp drop in temperature
Wednesday night as a dry air mass settles in behind the cold
front. Model guidance has trended warmer in recent days with its
forecast of low temperatures.  The NBM has now stabilized to around
50 F Wednesday night, give or take a few degrees.  Despite the
trend, there should still be a 30-35 degree diurnal swing for most
locations across central Illinois; perhaps less dramatic in areas
south of I-70. Unusually cool temperatures will then remain in place
for Thursday with afternoon highs around 70 F and lows in the middle
50s.

A double dip in the jet stream will help push another compact
shortwave trough and its attendant cold front through the Great
Lakes Friday morning/afternoon. Poor diurnal timing of the frontal
passage, as well as poor moisture-return will again limit
convective chances and QPF. The NBM currently advertises a low
(10-20%) chance of rain on Friday, but it would not be surprising
to see chances increase some in the next few days with the right-
entrance region of the upper jet streaking across central Illinois
(enhanced ascent).

Another stretch of dry, cool, and low-impact weather will return
to close out the week as the upper-level ridge and its associated
surface high pressure begin to build in from the west. Model
guidance is not clear with the evolution of this ridge through the
weekend, with some members of guidance (e.g. GFS, ECMWF AIFS)
drier than others (CMC, ECMWF). Either way, if you have been
mired in drought the past few weeks, there is no clear signal of a
drought buster on the horizon as we enter the middle of September.

MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1135 PM CDT Mon Sep 1 2025

A surface high pressure ridge over the area will shift slightly
southward over the upcoming day, causing winds to weaken and skies
to remain mostly clear. Winds NE up to 6 kts through Tuesday
morning, becoming light and variable.

37

&&

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

$$