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FXUS63 KILX 240450
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1050 PM CST Sun Nov 23 2025

.KEY MESSAGES...

- Dense fog reducing visibility to a quarter mile or less is
  possible (50-80% confidence) overnight into Monday morning
  across most of central Illinois.

- There is a greater than 90% chance for rain Monday evening and
  overnight. 25th-75th percentile rainfall ranges from 0.05-0.35
  in the northwestern counties to 0.25-0.75 in the southeast.

- Winds gusting 30-40 mph Wednesday will usher in cooler
  temperatures to end the week with widespread lows in the lower
  to mid 20s Thursday morning with Wind Chill Values in the teens.

&&

.UPDATE...
Issued at 806 PM CST Sun Nov 23 2025

A large area of stratus cloud cover with embedded pockets of dense
fog stretches from south-central IA to central KY, according to
difference channel and RGB satellite imagery, expanding northward
toward central and southeast IL. Across central IL, clear skies
remain, however dewpoints from the mid 30s to lower 40s should be
supportive of fog development as well, given the clear skies and
light winds. Have already seen patchy fog develop, especially in
southeast IL. As low pressure moves into the Plains tonight,
southerly winds should gradually increase, which would tend to
limit radiational fog, but also spread the deeper stratus/fog
region northward. The overall evolution of stratus/fog overnight
remains somewhat uncertain, but given rich moisture, decreasing
visibility, and numerous model guidance products suggesting dense
fog, have issued a Dense Fog Advisory from Knox County to Marshall
County southward until 10 AM Monday. Will watch for trends, and
may need to expand this advisory northward. Will also keep an eye
on potential for increasing winds to disrupt the dense fog
character and favor stratus with better surface visibility.

Lows ranging from mid 30s along and north of I-74 to lower
40s southwest of a Springfield-Effingham line look on track. These
temperatures should be reached late this evening, with little
additional cooling overnight as winds, stratus, and fog develop.

37

&&

.DISCUSSION...
Issued at 124 PM CST Sun Nov 23 2025

This afternoon, water vapor imagery reveals a closed upper low
over the Four Corners region which is progged to lift across the
central Great Plains tonight, then across central Illinois late
Monday night. At the surface, high pressure is analyzed over the
mid Mississippi Valley with ridging extending north across the
Upper Midwest. The ridge axis will shift east across central
Illinois this evening, with a modest southerly gradient
overspreading central Illinois from the west in its wake. Despite
the 5-8kt southerly wind developing late tonight, guidance is once
again hinting at widespread fog potential overnight into Monday
morning. 12Z HREF probabilities for dense fog (quarter or mile
less visibility) runs roughly 50-80% with the highest confidence
along the I-74 corridor and across portions of east central
Illinois (closest to the ridge axis).

Meanwhile, as the upper low approaches the region through the day
Monday, expect cloud cover to be on the increase followed by
precip chances starting late in the afternoon. PoPs peak Monday
evening and overnight in the 80-95 percent range within the
strong warm air advection ahead of the low. A few additional
scattered showers (30% coverage) Tuesday morning and early
afternoon are expected as the main upper wave passes over central
Illinois.

A northern stream shortwave trough is expected to move onshore
over the Pacific Northwest Monday and dig across the Upper
Midwest and Great Lakes late Tuesday into early Wednesday. A
surface low will deepen in response and push a strong cold front
across central Illinois Tuesday night. Warm air advection ahead of
the low may drive some very light rain or drizzle Tuesday but
precip is not expected with the cold front. Instead, a tight
pressure gradient associated with the deepening low and steep low
level lapse rates from the cold air advection will result in
moderately strong winds across central Illinois Tuesday night and
Wednesday. NBM probability of 24-hr peak gusts exceeding 30 mph is
greater than 90% and around 50-60% to exceed 40 mph. Much cooler
air will overspread central Illinois with highs near 60 degrees
Tuesday giving way to highs only in the upper 30s to mid 40s the
remainder of the week. Overnight lows in the 20s are likely with
wind chill values dipping into the teens at times Thursday through
Saturday mornings.

Next weekend, a very dynamic setup may take shape across the
region which would be capable of producing impactful winter
weather across portions of central Illinois. While it`s a bit far
out to get into details, accumulating snow changing to freezing
rain/rain through the day Saturday are advertised by some of the
latest models, so this period will bear watching as the details
come into better focus.

Deubelbeiss

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1050 PM CST Sun Nov 23 2025

Fog and low clouds are expected to spread over the area overnight,
with areas of dense fog possible. This should take place in the
next few hours as dewpoint depressions are small and an area of
deeper fog/stratus can be seen on satellite just south of KSPI,
moving northward. Conditions should deteriorate to LIFR by around
09Z. Improvement should begin after sunrise, but MVFR or worse
conditions are likely to continue through the period. There is a
low chance for rain showers to begin after 18Z, but mentionable
chances don`t start until after 21Z. By around 02Z, rain should be
predominant across the area. Winds S-SE around 5 kts overnight,
increasing to 10 kts by 15Z-17Z.

37

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST Monday for ILZ027-029-036-037-
040>042-047>054-056-061>063-066>068-071>073.

&&

$$