108
FXUS63 KILX 192317
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
617 PM CDT Tue Aug 19 2025

.KEY MESSAGES...

- The recent intense heat has come to an end...as readings drop
  back to near normal in the middle to upper 80s for the remainder
  of the week.

- A second cold front may trigger an isolated shower on Saturday,
  followed by even cooler highs in the 70s by early next week.

&&

.DISCUSSION...
Issued at 1253 AM CDT Tue Aug 19 2025

18z/1pm surface analysis shows a cold front approaching the I-70
corridor. The airmass ahead of the front remains oppressively hot
and humid with heat index values above 100 degrees. Meanwhile to
the north, winds have veered to the N/NW and air temps have fallen
into the lower to middle 80s. A band of enhanced Cu currently
accompanies the boundary, and this will be the area to watch for
widely scattered convection this afternoon. CAMs have consistently
focused the greatest areal coverage of showers/storms further
upstream across Indiana...and this seems reasonable given latest
satellite/radar trends. As a result, am carrying just 20-30 PoPs
along/south of a Paris to Taylorville line over the next couple of
hours, then lingering south of I-70 until about 02z/9pm. Skies
will partially clear and winds will decrease to 5mph or less
tonight. With ample boundary layer moisture still in place as
shown by surface dewpoints hovering in the middle to upper 60s,
the stage will be set for patchy fog development...particularly
where recent rainfall has been the heaviest. The models (other
than the GFSLAMP) are not advertising much fog: however, think
they are underdoing it and have thus added patchy fog to the
forecast along/north of the I-72 corridor toward dawn Wednesday.

Skies will initially be mostly sunny Wednesday morning: however,
the NAM Cu-rule becomes strongly negative as a trough axis
currently upstream across Minnesota/South Dakota drops southward
into Illinois. Based on forecast soundings, skies will become
partly to mostly cloudy for a time from late Wednesday morning
into the afternoon...and isolated showers cannot be ruled out by
peak heating. Several CAMs suggest a few showers during the
afternoon, especially along/west of the I-55 corridor. Areal
coverage will be minimal and any rainfall that occurs will be
light. Once the trough drops south of the region and high pressure
builds in from the north, dry and seasonably warm readings in the
middle 80s are anticipated for Thursday and Friday.

Further out, models are in excellent agreement that a vigorous
short-wave trough evident on current water vapor imagery off the
coast of British Columbia will track eastward over the next couple
of days, then dig into the Great Lakes over the weekend. This will
push a re-enforcing cold front into central Illinois on Saturday.
While recent runs of the NBM have been dry, several models are at
least hinting at widely scattered showers/thunder along the front.
Given favorable timing during peak heating, think a low probability
(20% chance) for convection is warranted with FROPA Saturday
afternoon.  Once the front passes, an even cooler/less humid
airmass will arrive by early next week...with highs dropping into
the 70s Sunday through Tuesday.

Barnes

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 617 PM CDT Tue Aug 19 2025

Area of MVFR ceilings is approaching KPIA-KBMI early this evening,
and will continue for a few hours. While this breaks up for a
time, ensemble guidance suggests another period early Wednesday
morning where ceilings drop below 3000 feet at these sites (50-70%
chance). Further south, any MVFR conditions would be more favored
as the diurnal cumulus field first develops around 15Z.

North winds will gradually turn more northeast overnight, picking
up to about 10 knots over eastern Illinois by midday Wednesday.


Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for ILZ066>068-071>073.

&&

$$