584
FXUS63 KILX 171044
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
544 AM CDT Fri Oct 17 2025

.KEY MESSAGES...

- Showers and a few thunderstorms will occur late tonight through
  Sunday morning. The latest indications continue to suggest
  locations along and southeast of a Champaign to Springfield
  line will see the heaviest rainfall in excess of 1 inch.

- There is a Marginal Risk (5-15% chance) for severe weather
  along/east of I-55 Saturday afternoon and evening...with the
  primary risk being damaging wind gusts.

&&

.SHORT TERM...(Today through Saturday)
Issued at 306 AM CDT Fri Oct 17 2025

Unseasonably warm weather will continue today as S/SE boundary
layer flow increases ahead of a slowly approaching cold front.
Thanks to a tightening pressure gradient, S/SE winds will gust
15-25mph everywhere north of the I-70 corridor. Despite occasional
bands of mid/high clouds which will result in partly sunny skies,
WAA ahead of the front will boost afternoon highs into the upper
70s and lower 80s.

As the front nears, all CAMs suggest scattered showers/storms will
develop across Iowa/Missouri this evening...then spill into the
western KILX CWA overnight. While the exact eastward extent of
the showers varies among the models, think a slower solution is
prudent given the highly amplified upper pattern. Have therefore
focused likely PoPs (60-70% chance) in the Illinois River
Valley...tapering down to just a slight chance (20%) as far east
as a Champaign to Taylorville line. Lows will range from the upper
50s near the Indiana border to the middle 60s in the Illinois
River Valley.

As Gulf moisture flows northward ahead of the front, NAM
precipitable water values increase from around 1.25 today to over
1.50 from Saturday morning into Saturday evening. Given increasing
deep-layer moisture, good convergence along the boundary, and
strong upper dynamics...the stage will be set for periods of showers
and thunderstorms on Saturday. Despite the favorable synoptic
pattern for rain, models generally struggle to properly initialize
antecedent dry soil conditions. Given the ongoing D2 and D3
drought across central Illinois, think model QPF remains too
high. In addition, consensus has favored an outbreak of severe
weather across the Ozarks and lower Mississippi River Valley for
the past several cycles. Widespread convective development
upstream across this area will likely impede northward moisture
transport. Am therefore favoring lower end rainfall guidance for
much of the area. The 12z LREF focuses the highest probabilities
(40-50% chance) for greater than 1 inch of rainfall along/southeast
of a Champaign to Springfield line...while the 00z HREF also keys
in on this area. At this point, think all of central and southeast
Illinois will see the first widespread significant rainfall in
over a month. However, do not feel the rain will be enough to
mitigate the current drought conditions. Most locations will see 1
inch or less...with higher amounts over 1 inch across the E/SE
CWA.

While deep-layer wind shear will increase markedly ahead of the
cold front and its associated upper trough on Saturday, instability
will remain meager given cloud cover and scattered convection
early in the day. The strongest shear/instability will co-exist
further upstream across Arkansas into western Tennessee/Kentucky
where severe thunderstorms will be likely during the afternoon and
evening. Further north, pockets of SBCAPE in excess of 1000J/kg
will support a few strong thunderstorms capable of marginally
severe wind gusts...particularly along/east of the I-55 corridor.
Any severe weather that materializes during peak heating will
quickly shift eastward into Indiana by mid-evening.

Barnes

.LONG TERM...(Sunday through Thursday)
Issued at 306 AM CDT Fri Oct 17 2025

Showers will linger into Sunday morning before cooler/drier
conditions return by afternoon. As low pressure deepens along the
departing front, strong NW winds will develop...with forecast
soundings and numeric guidance suggesting gusts of 30-35mph. Winds
will quickly subside by Sunday evening as high pressure passes
nearby, but will once again ramp up considerably from the south as
another fast-moving cold front approaches on Monday. After a
chilly day in the lower 60s on Sunday, temps will rebound into the
upper 60s and lower 70s by Monday. Once the second front passes,
the remainder of the week will feature much cooler weather with
highs in the lower to middle 60s and overnight lows in the upper
30s and lower 40s Tuesday through Thursday.

Barnes

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 544 AM CDT Fri Oct 17 2025

VFR conditions will prevail through the entire 12z TAF period.
S/SE winds of around 10kt early this morning will become S/SW and
gust 18-22kt from 14z/15z through the afternoon. Gusts will
subside toward sunset: however, the prevailing pressure gradient
supports continued sustained S winds of 10-12kt through the night.
BKN high clouds will stream across the sky for much of the
day...with clouds gradually thickening and lowering along/west of
I-55 overnight. 06z HRRR/NAM both indicate scattered showers
developing mainly in the Illinois River Valley late tonight. Given
the initially dry boundary layer, it will likely take some time to
moisten the profile and get rain down to the surface. Have added
VCSH at KPIA after 07z and at KBMI/KSPI after 10z accordingly with
cloud bases lowering to 4000-8000ft.

Barnes

&&

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

$$