369
FXUS63 KILX 281759
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1259 PM CDT Sat Jun 28 2025

.KEY MESSAGES...

- Above normal temperatures persist through the weekend, then a
  cold front will usher in seasonable temperatures with highs in
  the mid 80s during the first half of the week.

- Scattered showers and storms are possible today, near/south of
  I- 70. A better chance for precip exists area-wide late Sunday
  night into Monday (50-80% chance). A few strong to severe
  storms could occur.

&&

.DISCUSSION...
Issued at 240 AM CDT Sat Jun 28 2025

*** TODAY ***

A relatively zonal upper pattern is in place at the start of the
period, with the most notable sfc feature being a weak low (~1008
mb) north of the Great Lakes. A weak cold front extended southwest
from this low, and had stalled across the northern portions of
the ILX CWA Fri evening.

Keeping an eye out for patchy fog this morning, especially to the
northwest of the existing cloud shield (mainly NW of I-55). 28.00z
HREF produces higher probabilities of fog than previous
forecasts, with a 25-50% chance of vis below 1 mi NW of I-55.
There`s been no clear indications of fog development on NT
microphysics satellite imagery to this point, but a few locations
such as Galesburg and Macomb have reported visby reductions, with
the latter falling below 1 mi at 2am/07z. Added a mention of
patchy fog to the forecast, but at this point think dense fog
advisories are unlikely to be needed.

For today, forecast theta-e fields show the stalled front
gradually lifting just north of the ILX CWA this afternoon.
Storms are not expected to form along this front today due to weak
sfc convergence, limited mid-level forcing, and a subtle warm
nose around 800mb resulting in a modest cap. Across SE IL, some
scattered showers/storms could develop as convective temps are
reached, as fcst soundings show little to no capping in those
areas. The parameter space remains similar to previous days, with
moderate-high CAPE and weak shear, so isolated strong gusts are
once again a concern. Otherwise, highs remain near 90F, with
afternoon dewpoints around 70F, resulting in heat indices in the
mid-90s. Winds will be quite light today owing to the diffuse sfc
pattern.

*** SUNDAY - MONDAY ***

For Sun, a weak mid-level impulse could aid precip development
during the late morning/afternoon. Storms are also expected to
develop along a sfc front draped across WI/IA, but this is
expected to be well NW of the ILX CWA, at least through the day on
Sun. Ahead of that mid-level impulse, forecast soundings still
show weak lapse rates or subtle capping present above the cloud
base, which combined with limited sfc forcing should limit storm
coverage during the day. Given these mitigating factors, the NBM
PoPs seemed too aggressive, and PoPs were generally lowered to
near 30% for much of the area Sun afternoon.

Precip is more likely on Mon (60-80% east of IL River) as the
front sweeps through the ILX CWA. The exact evolution remains
somewhat uncertain as it is unclear how long the storms that
develop along the front Sun PM will persist, whether or not they
push into the ILX CWA Sun night, and whether or not they lay out
any outflow boundaries. Broadly speaking, the mid-level flow looks
a bit improved from previous forecasts, as a shortwave ahead of
the main trough is progged to have 30+ kt 500-mb flow. Moderate
instability and marginal deep layer shear (25-30 kts) could
support a conditional threat of strong/severe storms Mon PM. There
is a marginal risk (level 1 of 5) of severe storms late Sun night
NW of the IL River, and a marginal risk east of the IL River on
Monday. The main hazard with any such strong/severe storms is
damaging winds. The front is expected to push south of the ILX CWA
late Mon eve.

*** REST OF THE WEEK ***

The post-frontal airmass will be a respite from the heat/humidity,
offering more seasonable temps, with highs in the mid 80s, lows in
the mid 60s, and afternoon dewpoints in the mid 60s as well. Dry
conditions are also expected these days as weak sfc high pressure
(~1016 mb) shifts through the region. Looking ahead to the holiday
weekend, ens guidance generally suggests that an upper ridge will
shift across the Plains towards the Midwest, while a slow-moving
cut- off upper low sits near or over the Pacific NW. The approach
of that upper ridge lends confidence to a warming trend during the
latter part of the week/into next weekend, with ensembles
depicting a greater than 70% chance of above normal temps. The
upper pattern is such that occasional disturbances result in sfc
lows tracking north of the ILX CWA sometime during that period,
and these could pass close enough to offer precip chances. Ens
blends paint a 20-30% chnc of precip on the 4th, steadily
increasing through the weekend (30- 40% on Sat Jul 5, 40-50% on
Sun Jul 6). Confidence in the specifics of the precip forecast
remain low at this range.

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1255 PM CDT Sat Jun 28 2025

A boundary was south of I-72 at early afternoon extending along a
Taylorville to Lovington to Charleston to Chrisman line and has a
few convective cells recently devleping along it in NE Shelbyv and
western Moultrie counties. This bounday and more unstable air mass
to slowly sag southward this afternoon and evening, keeping
convection chances mainly south of I-72 but will be close to SPI
and DEC airports next few hours. Scattered to broken cumulus
clouds this afternoon with bases 2.5-3.5k ft early this afternoon
to slowly lift into VFR category during mid/late afternoon. More
isolated convection to return into sw IL Sunday morning, but
should stay sw of central IL airports until after 18Z/1 pm
Sunday. South to SE winds near 5 kts this afternoon to be light
and variable tonight and be south at 5 kts after 15Z/10 am Sunday.


07

&&

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

$$