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FXUS63 KILX 052331
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
631 PM CDT Sat Jul 5 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms will spread eastward into
  central IL this afternoon and evening and continue into Sunday
  (40-70% chance) as a cold front slowly moves into the area.
  Locally heavy rainfall, lightning and a few strong wind gusts
  are possible.

- Hot and humid conditions will continue Sunday south of I-72,
  with highs near 90 and afternoon heat indices in the mid 90s to
  near 100 degrees. More seasonably hot and humid conditions can
  otherwise be expected the next several days as a cold front
  brings slightly cooler conditions.

- Occasional periods of scattered showers and thunderstorms can be
  expected for the upcoming work week.

&&

.UPDATE...
Issued at 629 PM CDT Sat Jul 5 2025

The forecast remains largely on track. Increased PoPs (from 40-60%
to 60-80%) across our far west for a few hours this evening where
thunderstorms are rolling in, and also decreased them (from
30-40% to 15-25%) overnight as the CAMs are showing less coverage
than some of their earlier iterations - something that makes
meteorological sense given the lack of wind shear and loss of
diurnally-driven instability.

Bumgardner

&&

.DISCUSSION...
Issued at 221 PM CDT Sat Jul 5 2025

A cold front currently draped from northern WI southwestward
through IA and KS will be the focus for weather development over
the upcoming couple of days. Showers and thunderstorms ahead of
this feature continue to progress toward west central IL this
afternoon, and should begin to move into the IL River valley late
this afternoon or evening, slowly spreading eastward toward the
I-57 corridor and weakening overnight. Instability/CAPE will be
modest this evening, as high as 1000-2000 J/kg west of the IL
River, although deep layer shear will be under 20 kts. The most
favorable area for locally damaging wind gusts looks to be around
Knox and Stark Counties where SPC has a Marginal Risk for severe
storms designated. With precipitable water values potentially
exceeding 2 inches ahead of the front and slow storm motions,
locally heavy rainfall is a possibility. HREF ensemble
precipitation maximum depicts isolated 2-3 inch rainfall
accumulations, and WPC depicts a Marginal Risk for excessive
rainfall beginning in west central IL this afternoon, and
continuing through Monday for precipitation associated with this
front. Nevertheless, precipitation will be scattered and showery,
and average rainfall amounts through Sunday appear they will be
under a half inch. 1-hour Flash Flood Guidance values are around 2
inches.

As the front progresses into central IL Sunday, storms should re-
intensify with daytime heating, and CAPE values of 1000-2000 J/kg
with continued weak shear look to characterize the environment.
Again, locally heavy downpours in slow moving storms look to be
the main weather concern.

The front looks to stall out near southern portions of the
forecast area Monday, shifting rain chances mainly south of I-72.
As the work week progresses, a series of upper level waves should
move through the area in a weak zonal flow pattern, promoting
occasional scattered showers and thunderstorms. Exact timing
remains uncertain at this time for most of the week.

Temperatures will begin to trend downward slightly on Sunday with
the frontal zone, cloudy conditions and scattered showers over
the area. Highs look to range from 85 in Galesburg to 93 in
Lawrenceville. The work week looks to be characterized by
seasonably hot and humid weather for the week, with daily highs
from mid 80s to around 90, and lows mid 60s to around 70.

37

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 629 PM CDT Sat Jul 5 2025

A broken line of showers and storms located just east of the MS
River at 615pm will advance east over the next few hours, posing
a slight (30-40%) risk for lightning at PIA between 01-04z
(8-11pm) and a lower risk at the other terminals a bit later. As a
result, the prob30 for TSRA was maintained at PIA and omitted
elsewhere this evening, though VCSH was included at the other
sites for much of the overnight period when high resolution
guidance suggests widely scattered showers will be around; the
lower instability overnight suggests the probability of thunder
will be low (less than 10%). However, the risk will be renewed
tomorrow ahead of a nearly stalled cold front situated somewhere
in the vicinity of I-72 during the afternoon. As a result, prob30
groups were added to DEC and CMI (and considered, though
ultimately omitted, at SPI and BMI) for the last 4 hours of the
forecast period - from 20z Sun to 00z Mon (or 3-7pm Sun). HREF
suggests a 40-60% probability of MVFR ceilings during the morning
at PIA, and lower (20-40%) chances elsewhere. We`ll keep an eye on
forthcoming guidance to assess whether MVFR ceilings will need to
be added to the forecast at the other TAF sites. South-southwest
winds will ease this evening, veer to southwesterly tomorrow
morning, then veer further to westerly during the afternoon.

Bumgardner

&&

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

$$