410
FXUS63 KILX 172306
AFDILX

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

.KEY MESSAGES...

 - Showers and storms producing locally heavy rain will be
   possible Saturday afternoon and evening, particularly across
   east central and southeast Illinois, where isolated rainfall
   totals could exceed 1 to 2 inches in spots.

 - The risk for severe thunderstorms remains low, but a 5-14%
   chance of severe weather is possible Saturday afternoon/evening
   across east central and southeast Illinois.

 - Strong northwest winds with gusts of 30-40 mph are likely on
   Sunday, and a 30-50% chance exists for isolated gusts to reach
   or exceed 45 mph.

&&

.DISCUSSION...
Issued at 138 PM CDT Fri Oct 17 2025

This afternoon, high pressure stretches along the eastern
seaboard while low pressure is moving east across the Canadian
Prairies. Modest southerly flow across central Illinois ahead of
the low and attendant cold front along with increasing cloud cover
will result in mild conditions overnight with lows in the low to
mid 60s. Showers and thunderstorms are expected to increase in
coverage across Iowa/Missouri late this afternoon into the
evening, then will track into west central Illinois late tonight.
Convection will likely be in a decaying phase owing to the poor
diurnal timing. Through 12 UTC / 7 AM CDT Saturday morning,
precip is expected to advance as far east as the Illinois River to
I-55 corridor.

The initial wave of precip will continue to track east across the
state through the remainder of the morning and early afternoon
Saturday, but expect precip to expand in coverage late afternoon
and evening as a pair of phasing mid level shortwaves push across
the mid Mississippi Valley. PWats increase up to around 1.5 inches
ahead of these features, which is above the 90th percentile for
GEFS re-forecasts for mid October. In addition to the high
moisture content, mean cloud-bearing flow (850-300mb) looks to be
fairly parallel to the surface front which could result in some
training of storms. Some locally heavy rain could develop as a
result. HREF LPMM indicates some swaths of 1 to 2 inches (locally
higher) of rain will be possible, especially in portions of SE and
east central Illinois where precip timing better aligns with peak
heating. The severe threat remains a bit uncertain Saturday,
mainly due to concerns around the amount of instability. GFS
advertises only modest instability Saturday afternoon with MLCAPE
values less than 1000 J/kg. If we do realize the instability,
shear will be favorable to support a severe weather threat. 0-6km
shear vectors are expected to increase to around 30-40 kt in
magnitude with 15-25 kt in the lowest 0-1km. Poor lapse rates
resulting in "skinny" CAPE profiles do not appear overly
supportive of hail, and only marginally supportive of damaging
wind gusts. Wouldn`t be surprised to see the severe outlook for
Saturday be further trimmed from the northwest with additional
updates, but a 5% risk seems reasonable still, especially across
east central and southeast Illinois.

In response to the aforementioned shortwaves, surface low will
deepen to our east Saturday night into Sunday resulting in a tight
pressure gradient and 2-4mb/3hr pressure rises overspreading
central Illinois in its wake Sunday. Moderately strong winds will
be the result Sunday. Cold-air-advection driven steep low level
lapse rates will also be in place allowing mixing down of winds
aloft in the 35-40 kt range Sunday afternoon. A few wind gusts
reaching or exceeding wind advisory criteria (45 mph) cannot be
ruled out (30-50% probability from the NBM roughly along east of
I-55). The breezy northwest wind will keep temperatures suppressed
through the day Sunday with highs struggling to reach the low
60s.

Another upper level disturbance, at times a closed upper low, is
expected to dig across the Great Lakes Monday night into Tuesday.
Strong warm air advection ahead of this system will briefly drive
temps back up to around 70 degrees Monday afternoon. A few showers
are possible within the mid level WAA Monday evening, followed by
additional precip chances Tuesday as cold air advection again
drives steep low level lapse rates and weak diurnal instability.
The ECMWF is most bullish on precip chances as far south as
central Illinois, while the GFS and GEM favor precip mainly to our
north.

Deubelbeiss

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 606 PM CDT Fri Oct 17 2025

Lowering/thickening high to mid level clouds and south winds
around 10 kt will prevail over the central IL terminals this
evening. By late tonight, scattered showers/storms associated with
a pre-frontal trough will begin to move into central IL, gradually
shifting east through Saturday morning. TSRA coverage is expected
to be fairly low so kept the thunder mention to PROB30. Most CAMs
show a general lull in activity late morning through much of the
afternoon. However during this period ceilings will be lowering,
with MVFR becoming more likely by early evening. More widespread
SHRA with embedded TSRA are likely to move in from the south just
beyond 00z/Sunday, when low pressure approaches and deepens across
the region.

25

&&

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

$$