394
FXUS63 KILX 042331
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
631 PM CDT Fri Jul 4 2025

.KEY MESSAGES...

- Dry conditions are expected through Saturday morning across
  central and southeast IL, then chances for showers and
  thunderstorms develop from the Illinois River westward by
  Saturday afternoon.

- A better chance of showers and thunderstorms develops Saturday
  night into Monday (30-60% chance) as a cold front slowly moves
  through the area. Locally heavy rainfall, lightning and a few
  strong wind gusts are possible.

- Hot and humid conditions will prevail this 4th of July holiday
  weekend, with highs in the lower 90s and afternoon heat indices
  in the mid 90s to near 100 degrees.

&&

.DISCUSSION...
Issued at 232 PM CDT Fri Jul 4 2025

A high pressure ridge that has been keeping dry conditions across
central IL is slipping to the east of IL today, and will be replaced
by a low pressure trough currently emerging from the Rockies into
the Plains, and it`s attendant cold front, affecting central IL
over the weekend. The front itself looks timed to arrive in
central IL late Saturday night, and slowly work its way southward
into Monday, perhaps stalling out somewhere across central or
southern IL Monday. Stronger upper level flow with this system
looks to remain farther to the north, keeping deep layer wind
shear on the low side for central IL, around 20 kts or less,
however precipitable water of around 2 inches, or nearing
climatological maximum, will allow for CAPE of 1000-2000 J/kg and
heavy rain rates. HREF ensemble max precipitation is indicating we
could see some isolated 2 inch rainfall accumulations in the
Illinois River Valley Saturday evening, although widespread
rainfall should be much more subdued, generally under 1/2 inch.
Given these parameters not very supportive of severe weather, SPC
does not indicate 5 percent or higher probabilities for severe
weather for most of central IL, except in and around Knox County
where proximity is closer to slightly more favorable conditions.
WPC has a Marginal Risk for excessive rainfall on Sunday into
Monday in central/SE IL. Timing for initial storms ahead of the
front looks to be in the afternoon or early evening west of the
Illinois River, then gradually shifting southeastward toward the
I-70 corridor through the night. With the front over the area
Sunday, we should see scattered storm re- development as daytime
heating occurs, diminishing Sunday night.

Behind the late weekend system, the upper level pattern over the
region looks to transition to a weak zonal flow with embedded
shortwaves. This will keep chances for precipitation in the forecast
for much of next work week, pending better timing information that
will not be apparent until much closer range. Severe weather
probabilities look to be on the low side, unless local enhancement
of shear profiles develops in the vicinity of any shortwaves or
convective systems.

Temperatures and dewpoints will be above climatological normals
through Saturday (Sunday in southeast IL) ahead of the cold front as
warm and moist southerly flow continues. Expect heat index values
from mid 90s to near 100 with dewpoints near 70 degrees during
afternoon periods. Highs in the lower to mid 90s, lows lower to mid
70s. Following the cold front, temperatures and humidity look to
decrease slightly to near climatological norms (but still quite warm
and humid) for next work week. Highs mid 80s to around 90, lows
mainly upper 60s.

37

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 631 PM CDT Fri Jul 4 2025

A ridge of high pressure will once again ensure VFR conditions
for most, if not all, of the flight period. Near the end of the
forecast period (00z Sun, or 7pm Sat), isolated convection will
approach from the northwest, posing the greatest chance (20%) of
a shower or storm at PIA. The only other noteworthy mentions will
be the return of diurnal cu around FL050 (PIA) to FL060
(elsewhere) and southwest winds gusting to nearly 20 kt after
around 16z (11am) tomorrow.

Bumgardner

&&

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

$$