577
FXUS63 KILX 221050
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
550 AM CDT Fri Aug 22 2025

.KEY MESSAGES...

- There is a 15-20% chance for visibilities less than 1/2 mile in
  patchy fog this morning. Drivers and pedestrians should use
  extra caution, leaving extra time for the morning commute.

- After isolated showers and storms on Saturday (20% chance),
  conditions will turn dry and seasonably cool with overnight
  lows dipping into the upper 40s to low 50s by next work week.

&&

.DISCUSSION...
Issued at 105 AM CDT Fri Aug 22 2025

***** FOG THIS MORNING *****

At 1am, clear skies were evident on nighttime microphysics
satellite, with light winds also contributing to favorable
radiational cooling. Dewpoint depressions at surface obs are
running 1-3 degrees, and with lots of night left thinking is these
will diminish further - to 0 in many locations - by sunrise when
HREF suggests 20% chances for sub 1/2 mile visibility, highest
chances I-74 corridor and north. We`ll continue to monitor
visibilities at these sites and satellite (for extent of fog), and
if necessary issue a Dense Fog Advisory.

The upper ridge axis will shift across the region today, maintaining
dry mid to upper levels but also sufficient subsidence to keep in
place the low level inversion - maintaining shallow mixing. The
result: a pleasant day featuring scattered to numerous low clouds,
light winds, and afternoon high temperatures in the low 80s.

***** FEW SHOWERS/STORMS SATURDAY? *****

Tomorrow, westerly winds will advect a slightly more humid airmass
into the region ahead of an encroaching cold front associated with a
seasonably strong upper level trough centered over Hudson Bay.
Dewpoints will rise into the mid to upper 60s ahead of the front,
resulting in 1500-2000 J/kg SBCAPE. This may foster a couple
showers/storms, but most guidance is dry, perhaps because the best
forcing - associated with a prefrontal trough - will actually be
ahead of this more humid airmass. Nevertheless, with a couple CAMs
showing a storm or two, we elected to maintain ~20% PoPs area wide.
By definition, this suggests the probability of not having
measurable precipitation is 4 times as high as the probability of
having it; in other words, most folks will not see rain.

***** COOL AND DRY NEXT WEEK *****

After a second day of high temperatures in the low to mid 80s
Saturday, conditions turn cooler behind the front on Sunday and
even more so behind a secondary surge of cold air advection on
Monday. High temperatures Sunday will be mainly in the mid to
upper 70s, while on Monday the forecast has highs barely touching
70 along the I-74 corridor. Monday and especially Tuesday nights,
surface high pressure will favor lows in the low 50s to upper 40s;
NBM probabilities for sub 50 degree lows is 20-30% and 30-40%
each night, respectively. All the while, the dry airmass is
slated to keep the area precipitation-free with less than a 10%
chance for rain each day.

Bumgardner

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 549 AM CDT Fri Aug 22 2025

Patchy fog has made for a complicated forecast this morning, as
it`s developed rapidly and HREF guidance suggests it will be
at its worst around 11-13z (6-8am), then quickly dissipate. Added
TEMPO groups to each TAF through 13z to account for potential
visibility drops during this time. As this fog lifts into stratus,
there will be a 30-50% chance for MVFR ceilings for a few hours
this morning, before cloud bases rise into the VFR category.
Thereafter, VFR flight conditions should be predominant throughout
the remainder of the TAF period.

Bumgardner

&&

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

$$