561
FXUS63 KILX 031849
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
149 PM CDT Wed Sep 3 2025

.KEY MESSAGES...

- A cold front will bring a 60-80% chance for showers and
  thunderstorms to central Illinois late this afternoon and
  evening. Severe weather and widespread heavy rain are not
  expected, but localized pockets of 1-2 inches of rain and 30 to
  50 mph wind gusts will be possible.

- Well below normal temperatures with highs in the upper 60s to
  mid 70s will be in place Thursday through the weekend.

&&

.DISCUSSION...
Issued at 144 PM CDT Wed Sep 3 2025

This afternoon, low pressure is located just east of Lake Superior
with a cold front draped southwest across northern Illinois into
north central Missouri. A band of light shower or sprinkles is
currently ongoing near the Illinois River Valley ahead of the
front, but expect additional development through the mid to late
afternoon hours near the front. Regional obs show dew points
pooling in the low to mid 60s near the front contributing to
modest instability. Latest RAP forecast suggests around 500-700
J/kg MLCAPE will overspread central Illinois through the mid to
late afternoon hours and continue into this evening, along with 25
to 30 kt deep layer shear. While this parameter space does not
support widespread severe weather, an isolated stronger storm or
two will be possible with gusty winds the main hazard. Similar to
previous runs, the 12Z HREF suggests a few pockets of up to around
50 mph winds will be possible with the strongest storms. In
addition, HREF LPMM suggests a few isolated pockets of 1.0-1.5
inches of rain will be possible in the strongest storms, though
mean QPF values are more in the range of a quarter to half an
inch and not all locations will see precip. A modest northwest
breeze with gusts of 20 to 25 mph will overspread central Illinois
late this evening and overnight in the wake of the front. This
will help advect cooler temps into the region with lows dipping
into the 40s north of I-72.

Surface front will spread south across the Ohio Valley Thursday
while high pressure builds back across the Midwest in its wake.
Cooler temperatures and notably lower dew points will be
associated with this air mass. Temps will range in the 40s north
of I-72 and 50s south Thursday morning. High temperatures will
only be the low 70s Thursday afternoon while dew points mix down
into the 40s. Meanwhile, another shortwave trough is progged to
dig into the Upper Midwest Thursday then move east across the
Great Lakes Thursday night. A surface low will develop in
response, tracking from southern Minnesota Thursday evening to
Lake Michigan overnight while a trailing cold front pushes across
central Illinois. Central Illinois will be displaced from the
stronger forcing associated with the upper wave well to our north,
and unfavorable diurnal timing along with poor trajectories for
any notable moisture return will keep instability negligible.
These factors favor a dry frontal passage for most of central
Illinois. As the front lay out across southern Illinois during the
day Friday, modest isentropic ascent along the 305-310K surfaces
may support some light rain, mainly south of I-72 Friday
afternoon and evening.

Yet another shortwave is progged to round the base of the longwave
trough over the Great Lakes this weekend. No precip is expected
locally with this wave but it does reinforce the dry and cooler
air mass over the region as surface high spreads from the Canadian
Rockies Saturday to the mid/upper Mississippi Valley late Sunday.
The ridge will slowly shift towards the lower Great Lakes through
the first half of next week. Dry weather remains favored under
the influence of the ridge, but temperatures should begin to
moderate through the first half of next week with temps returning
to near normal by Tuesday and Wednesday.

Deubelbeiss

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1253 PM CDT Wed Sep 3 2025

A cold front poised upstream across Iowa will trigger scattered
thunderstorms late this afternoon and evening as it drops slowly
southward into central Illinois. 1730z/1230pm radar mosaic shows a
few light showers spilling into the Illinois River Valley...with
isolated convection beginning to re-develop further north immediately
along the boundary in the vicinity of KCID. Most CAMs suggest a
broken line of cells will form along the front over the next 2-3
hours, but will remain north of the central Illinois TAF sites
until after 21z. Based on a slight slowing trend noted by the
HRRR/RAP, have focused thunder at KPIA between 21z and 00z...then
further southeast to KCMI between 00z and 04z. Winds ahead of the
front will be westerly with gusts of 15-20kt this afternoon. Once
the front passes, winds will veer to NW and decrease to 10kt or
less across the board after midnight.

Barnes

&&

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

$$