947
FXUS63 KILX 292301
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
601 PM CDT Wed Jul 29 2026

.KEY MESSAGES...

- Comfortable weather through Thursday: Dry conditions and low
  humidity will persist across central and southeast Illinois,
  with high temperatures in the mid-80s and light winds.

- Heavy rainfall potential and tracking uncertainty: A slow-
  moving system will bring heavy rainfall and tropical-like
  moisture Friday into Saturday, creating a risk for localized
  flooding and road ponding. High confidence for widespread
  rainfall exceeding 1" targets areas near and north of I-74,
  while confidence decreases south of this corridor where
  lighter amounts (0.50" to 0.75") are expected depending on the
  low`s track.

- Cooler weekend, warming next week: Cloud cover and rain will
  keep weekend highs capped in the mid-to-upper 70s before dry,
  seasonably warm weather returns early next week.

&&

.DISCUSSION...
Issued at 100 PM CDT Wed Jul 29 2026

.Comfortable Summer Weather Persists Through Mid-week...

Cooler and drier weather will prevail across central and
southeast Illinois through Thursday. Surface high pressure (1016
mb) anchored over the region will maintain dry conditions
upstream of the upper-level ridge axis currently positioned over
the Northern Plains. Under this influence, afternoon highs will
generally climb into the mid 80s, while light winds and
favorable radiational cooling allow overnight lows to dip into
the low-to-mid 60s (with some upper 50s possible in east-central
Illinois). Comfortably low humidity will hold firm as dewpoints
stay largely in the upper 50s to low 60s.


.Cooler and Wetter To Close the Week...

The synoptic pattern transitions by Friday as a pair of
shortwave troughs, including a convectively-augmented feature
cresting the ridge axis, consolidate and dig across the Mid-
Mississippi Valley. The attendant surface low (~1005 mb) and
slow-moving cold front will cross Illinois through Saturday
morning.

A moisture-laden air mass will wrap into this synoptic engine,
driven by Gulf moisture return and localized evapotranspiration.
Forecast soundings point toward a very efficient warm-rain
setup characterized by anomalously high PWATs (1.7-2.1 inches),
long-skinny CAPE profiles, and deep warm-cloud layers.
Unmitigated moisture transport will favor heavy rainfall
efficiency, though convective intensity will be suppressed by
poor mid-level lapse rates and a diurnally unfavorable frontal
timing.

Considerable ensemble spread persists regarding the track of
the surface low:

EPS Solution (Deeper/Northern Track): Tracks the surface low
closer to the I-74 corridor, orienting the heaviest
precipitation axis from roughly Galesburg to Champaign with mean
QPF exceeding 1".

GEFS Solution (Weaker/Southern Track): Suppresses the surface
low further south toward St. Louis, shifting the main rainfall
band to a Macomb-to- Effingham line and capping mean QPF between
0.50" and 0.75".

Cloud cover and widespread precipitation will keep Friday and
Saturday daytime temperatures constrained to the mid-to-upper
70s. As the system`s deformation zone and upper trough axis
slide across the Wabash River Valley, low stratus and scattered
rain showers will linger into Saturday afternoon across eastern
Illinois before dry air takes over.


.Heat and Humidity Return By Mid-next Week...

Upper-level height rises and an amplifying western ridge will
build back into the Great Lakes early next week, bringing a
return to seasonably warm and dry weather for Monday and
Tuesday. The next opportunity for showers and thunderstorms
arrives mid-week as a robust northern-stream shortwave drives a
cold front into the Upper Midwest. However, confidence in
frontal penetration into central Illinois remains low as primary
upper-level forcing rapidly displaces east.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 601 PM CDT Wed Jul 29 2026

VFR conditions are expected through the TAF period as we remain
under the influence of high pressure. Northeast winds this evening
will become light and variable overnight, taking on a east-southeast
direction by Thursday morning.

&&

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

&&

$$

KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...NMA