945
FXUS63 KILX 261730
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1230 PM CDT Sat Sep 26 2026

.KEY MESSAGES...

- Expect mostly dry conditions and mild temperatures through
  Tuesday afternoon, though a few light showers are possible
  west of Interstate 55 today.

- Heavy rainfall and localized flooding become the primary
  concern Wednesday through Friday as repeated rounds of rain
  move across central Illinois.

- There is a 25% to 50% chance of rainfall exceeding 2 inches
  between Wednesday morning and Saturday morning, with the
  highest amounts expected northwest of the Illinois River
  Valley.

&&

.UPDATE...
Issued at 1040 AM CDT Sat Sep 26 2026

Another nice early fall day unfolding across central and
southeast IL with 1025-1027 mb Canadian high pressure near James
Bay and western Quebec/eastern Ontario province that drifts
slowly eastward during this weekend while ridging back into IL.
Mid level convergence and moisture advection band producing
scattered showers and a few thunderstorms from central/eastern
OK/KS northward into MO, central Iowa and central/sw MN. These
showers have been primarily just west/sw of CWA so far this
morning closer to MS river valley. Broken to overcast mid level
clouds from Galesburg to Taylorville and Olney west/sw while
partly to mostly sunny skies east/ne where mainly some high
clouds and scattered lower clouds in southeast IL. Latest CAMs
show chances of light rain showers as far east as a Galesburg to
Springfield line this afternoon into tonight with much of area
staying dry. More mid level clouds over western/sw CWA to keep
cooler highs in upper 60s to around 70F, while low to mid 70s
central and eastern CWA where more sunshine expected. Fairly
light and persistent east to NE winds to keep comfortable
dewpoints in the upper 40s to mid 50s, lowest in eastern IL.

&&

.DISCUSSION...
Issued at 251 AM CDT Sat Sep 26 2026

An expansive upper-level blocking pattern continues to govern
the regional weather regime, effectively sandwiching central
Illinois between a deep coastal low (Nor`easter) tracking along
the Mid-Atlantic/New England seaboard and a shortwave trough
lifting northward across the Great Plains toward the Upper
Mississippi Valley. Mid-level moisture advection associated with
the western shortwave is spreading eastward into the local
forecast area, though it encounters a deeply entrenched dry sub-
cloud layer across eastern Illinois, where gentle easterly flow
continues to advect in dewpoints in the upper 40s.

Subtle mid-level convergence atop this dry boundary layer will
support scattered, high-based showers this afternoon and
evening, primarily west of Interstate 55. Weak atmospheric flow
will result in slow-moving or training cell motion. This
prolonged residence time over localized corridors could
sufficiently erode the near- surface dry air to yield measurable
precipitation across our western counties.

Highs today will feature a cloud- and precip- driven gradient,
ranging from the upper 60s west of I-55 to the mid-70s eastward
where dry air and sun persist longer.

For Monday, persistent blocking maintains generally tranquil
conditions across the region. Expect variable cloudiness and
occasional light sprinkles, with seasonable high temperatures
holding in the low-to-mid 70s under a light easterly surface
wind.

The benign pattern will collapse rapidly by Tuesday as global
guidance aligns on strong shortwave energy ejecting out of the
Southwest U.S. ahead of a broader parent trough. Warm air and
moisture advection ahead of this swift-moving feature will boost
Tuesday afternoon highs into the upper 70s. As the attendant
cold front approaches, elevated ascent will saturate the column,
bringing increasing rain chances from west to east Tuesday
evening into Wednesday as the front slowly creeps into central
Illinois.

Hydro concerns take center stage Wednesday through Friday as
the frontal boundary decelerates and becomes quasi-stationary
across the forecast area, orienting nearly parallel to the
upper-level flow. Global deterministic guidance strongly favors
the southwestern upper trough phasing with Tropical Depression
Polo. This tropical interaction will transport a deep reservoir
of moisture northward along the stalled baroclinic zone.

Repeated rounds of rainfall look increasingly probable
Wednesday through Friday as the core shortwave advances
sluggishly along the wavering front. High rainfall efficiency
and training showers will make localized flooding our primary
concern through late week, as weak instability and shear
parameters keep the severe weather threat low.

The potential for heavy rainfall is well-represented in current
NBM probabilities, which indicate a 25-50% chance of 72-hour
rainfall totals exceeding 2 inches between Wednesday morning and
Saturday morning. The highest probability axis favors areas
northwest of the Illinois River Valley, with lower probabilities
anchored over southeast Illinois. Precipitation chances should
slowly wane into next weekend as Polo completes its
extratropical transition and the main trough kicks east.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1230 PM CDT Sat Sep 26 2026

VFR condtions are forecast to continue across the central IL
terminals through 18Z/1 pm Sunday. Broken to overcast mid level
clouds with bases of 7-12k ft to affect areas from PIA and DEC
west, and be most prominent at SPI next 24 hours. Northeast
airports of BMI and CMI may periodically see brief broken mid
level clouds but mainly more scattered mid/high clouds there.
Latest CAM runs like HRRR model keep isolated light showers
west/sw of central IL airports through this evening, though will
be closest to SPI airport. Canadian high pressure over eastern
Ontario and western Quebec provinces and ridging into IL through
midday Sunday to keep fairly light east to ENE winds 3-8 kts.

&&

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

&&

$$

KEY MESSAGES...MJA
UPDATE...07
DISCUSSION...MJA
AVIATION...07