895
FXUS63 KILX 210541
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1141 PM CST Thu Nov 20 2025

.KEY MESSAGES...

- Widespread fog will persist through Friday morning. The lowest
  visibilities of less than 1/2 mile will be focused across the
  heart of central Illinois from Rushville/Jacksonville
  northeastward through Champaign/Danville.

- Rain will lift into the region Friday morning, with the highest
  rainfall totals expected to be south of a Quincy to Terre Haute
  line where there is currently a high (60-90%) chance of
  exceeding 0.50"; source 06z REFS.

- A sharp cold front will push through by the middle of next week,
  sending overnight temperatures into the 20s by Thursday morning;
  source 13z NBM.

&&

.UPDATE...
Issued at 737 PM CST Thu Nov 20 2025

Thanks to a very moist boundary layer and only very light S/SE
winds to the north of a stationary frontal boundary, widespread
fog is noted across central Illinois early this evening. While
visibilities have generally ranged from 1 to 3 miles, two
persistent pockets of visbys under 1/2 mile have developed. One is
focused along I-74 from Bloomington to Champaign and the second is
further west around Quincy and Pittsfield. The forecast for the
remainder of the night is a bit tricky as CAMs are not handling
the current situation particularly well: however, given the
synoptic set-up north of the front, think fog will continue to
thicken across the heart of central Illinois and the two areas of
lowered visbys will eventually congeal. As a result, have opted to
issue a Dense Fog Advisory for locations along/north of a
Jacksonville...to Decatur...to Danville line...and along/south of
a Macomb to Bloomington line. Visbys within this area will drop to
1/2 mile or less and remain low until showers developing further
south across Missouri eventually spread northward into the
southern half of the KILX CWA after midnight. Outside the
Advisory, 1-3 mile fog will persist.

Erwin

&&

.DISCUSSION...
Issued at 121 PM CST Thu Nov 20 2025

Low clouds and patchy drizzle will persist through this evening
across central and southeast Illinois as we get spurious periods
of sufficient upward omega through an otherwise non-uniformly
saturated near-sfc layer (0-1.5 km). The primary impact will be to
general aviation, though motorists may experience damp pavements
and occasional reductions in visibility.

Our main weather story comes tonight into Friday.

New guidance trends indicate a tighter gradient in Quantitative
Precipitation Forecast (QPF) along the northern edge of our
approaching frontal system, alongside a slightly delayed onset of
precipitation. The reasons for this shift are evident in this
afternoon`s mid-level Water Vapor (WV) imagery, which highlights
the impending clash of two notable features over the Midwest late
tonight.

The first feature is a negatively-tilted trough pivoting across
the Big Bend region of Texas. This trough is drawing both Pacific
and Gulf moisture northward into the Southern Plains and will be
the primary driver of rain chances into Friday as it lifts toward
our area. The second is a dry, subsident air mass pushing
southeastward into the Great Lakes region.

As these two air masses phase together late tonight, a sharp
north-south rainfall gradient is expected to develop, roughly near
or just south of a Quincy-to-Terre Haute line. Recent LPMM QPF
output from both the REFS and HREF ensembles strongly supports
rainfall totals between 0.25"-1.25" south of this line, with
amounts quickly diminishing to 0.10" or less with northward
extent.

The upcoming weekend will see a return to dry and mild weather as
the departing frontal system gives way to high pressure building
across the central US. Expect afternoon temperatures to warm into
the mid-to-upper 50s on both Saturday and Sunday, driven by low-
level warm advection beneath an amplifying ridge axis.

Our attention then shifts to the Monday night-Wednesday timeframe
with the arrival of another frontal system ejecting out of the
Southern Plains and lifting across the area. Convective chances
and moisture return ahead of this system appear limited, which may
keep Quantitative Precipitation Forecast (QPF) totals in the
0.1"-0.5" range. The more significant aspect of this system will
be the dramatic temperature shift. A sharp cold front is expected
to move through on Wednesday, ushering in blustery northwest winds
and causing overnight lows to bottom out in the 20s, just in time
for Thanksgiving Day.

MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1141 PM CST Thu Nov 20 2025

IFR conditions will persist across the area overnight. The latest
guidance suggests ceilings will climb back to MVFR at KPIA by
late morning/early afternoon then further south to the I-72 sites
by late afternoon/early evening. Visibilities at most terminals
are below 1 mile late tonight, with little improvement until rain
spreads northward later this morning. Winds will be light through
tonight, becoming northeasterly with speeds around 10 kt or less
during the daytime hours.

Barnes/NMA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CST Friday for ILZ031-036>038-
040>057-061.

&&

$$