032
FXUS63 KILX 070512
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1112 PM CST Sat Dec 6 2025

.KEY MESSAGES...

- A wintry mix is expected tonight into Sunday morning. Snow
  accumulations of 1-3" are most likely north of a Galesburg to
  Pontiac line. Further south, a glaze of ice is possible. This
  includes areas from Galesburg and Pontiac south to a Beardstown
  to Mattoon line. A winter weather advisory is in effect for
  these areas.

- The pattern remains unsettled, with two additional disturbances
  during the middle of the week. The first is expected to produce
  primarily rain Tues night-Wed (30-50% chance), then the second
  could produce light snow Wed night-Thurs (30-40% chance).

- Temperatures moderate by mid-week, with highs reaching the 40s.
  Below normal temperatures return late in the work week.

&&

.UPDATE...
Issued at 902 PM CST Sat Dec 6 2025

Challenging update as air temps are starting to slowly rise this
evening at some sites, especially in the west. Areas in the east
have not bottomed out yet, but believe these areas will see slowly
rising temps overnight as well. More temps at or above 32F would
prevent more freezing rain/drizzle. However, snow still appears
likely in the north overnight.

Speaking of precip. Even though radar is showing some returns over
area northwest of the IL river, surface reports of precip in those
locations has not occurred yet. Model soundings at ILX and DVN do
show some dry air that needs to be overcome before precip starts
reaching the ground. Observations show lowest cigs in the
northwest of around 6kft with sites further east of 10kft or
higher. So, observations indicate there is still quite of bit of
dry air to overcome.

Based on these observation and HiRes model solutions, believe
precip will still not for several more hours, like just before or
around midnight in the north and west, with after midnight in the
northeast. Temps in the north are still below freezing, so think
the winter weather advisory is still valid for now.

Overall the current forecast looks fine, but will try to spruce up
the hourly temps and pops for the remainder of the night. Update
should be out shortly.

Auten

&&

.DISCUSSION...
Issued at 118 PM CST Sat Dec 6 2025

*** THROUGH SUNDAY ***

Temperatures this afternoon exceeded expectations, at least across
the southern half of the CWA, as a period of mostly clear skies
allowed temps to climb into the mid/upper 30s. This has led to
some snowmelt, with melting visually evident in satellite imagery
near I-70, and reduction in the snow depth further north. Snow
depth at NWS Lincoln was down to 3" at midday, compared to 4" over
the last several days.

A clipper system, in the form of a sfc low currently over
Nebraska, remains on track to bring a wintry mix to the area
tonight into Sunday morning. The biggest change this forecast
cycle was a tightening of the QPF gradient, with a continued
slight northward trend in the track of the low. This slight
northward shift also increases the potential fog advection fog
tonight (more on that below).

The precipitation type forecast remains complex with this system.
As precip pushes in from west to east tonight, the temp profile
appears just cold enough to favor snow, but some fcst soundings
quickly develop a weak warm level warm nose which could lead to
freezing rain or just rain mixing in. Latest guidance focuses the
snow accums mainly near/north of a Galesburg to Pontiac line
(1-3", increasing to higher amounts as you approach I-80
corridor). With southward extent, snow probs drop sharply, with
the latest NBM having a 30% chance of 1" at Peoria and just a 10%
chance in Bloomington-Normal.

There is also concern for a period of freezing drizzle as the
column desaturates from top down, leading to a loss of cloud ice.
Sfc temps near freezing further complicate determining whether
drizzle or freezing drizzle will occur. Latest high-res guidance
continued to trend slightly warmer from previous forecasts,
suggesting temps a few degrees above freezing. I share the
previous forecasters line of thinking that the snow cover and
frozen ground will hold temps near or just below freezing, but the
trend toward warmer conditions in the models and the
overperformance of temperatures today decreases confidence in that
assessment. Given the shifts north and the tightening of the QPF
gradient, am least confident in ice occurring in the southeastern
portions of the winter weather advisory (Coles to Edgar County and
south). Those areas may wind up seeing little to no wintry
impacts out of this system. Elsewhere within the advisory area, a
glaze of ice still appears likely, which will result in very
slippery conditions.

Precip should largely diminish into the late morning/afternoon,
although some lingering drizzle or flurries are possible
immediately behind the cold front (mainly across SE IL). Drizzle
will likely occur at first, then transition to flurries as CAA
results in the saturated low-level layer cooling enough for cloud
ice to return.

There is potential for advection fog tonight into Sun morning.
The northward shift in the low track has also resulted in greater
low-level moisture advection, with latest HREF mean indicating
dewpoints of 33 or 34 degF advecting into eastern IL overnight (up
a few degrees from previous cycle). With the existing snow pack
and frozen ground, this could support fog development, including
dense fog, despite plenty of mid/upper level cloud cover
overnight. Areas across SW MO, SE KS, and OK experienced dense fog
Sat AM, although there was less mid/upper clouds in those areas
this morning than is forecast here overnight, so its not a perfect
comparison. The HRRR, RAP, and NAM suite all suggest dense fog
development east of I-55, while other guidance sources have little
to no fog, so this seems like an all or nothing scenario where
there is widespread dense fog east of I-55, or little to no fog.
The latest HREF currently has a 30-50% chance of vis below 1 mile
east of I-55, although as previous shifts noted, the modeled sfc
temps may be a tad too warm due to the existing snowpack.

Following the cold frontal passage on Sunday, bitter cold air
returns by Sunday night, with single digit lows north of a
Macomb- Bloomington line, teens along the I-72/Danville corridor,
and 20s near/south of I-70. Wind chills could fall a few degrees
below zero.

*** MONDAY - FRIDAY ***

As ridging remains anchored out west, a broad northwest flow
regime and baroclinic zone will exist from the Pacific NW to the
Ohio Valley, resulting in continued clipper systems passing by
throughout the week. The next such system is tracking such that
moderating temps are forecast mid-week (highs in the 40s Tues-
Wed). This will favor rain as the primary p-type Tues night into
Wed, although a rain-snow mix can`t be ruled out during the
nighttime hours, especially north of I-74 where it will be
coolest. Another weak clipper will follow quickly behind this one,
and could offer a chance for snow Wed night-Thurs. Currently,
snow accums from this system appear minor, with a 30-50% chance of
a dusting but less than a 20% chance of 1".

The latest guidance has trended towards a deep cut-off low digging
into the Midwest by late in the week, bringing a strong cold front
through and ushering bitter cold air back into the region. Will
note that this has not yet been a consistent feature from run-to-
run, but it certainly bears monitoring. If the latest guidance is
to be believed, high temps may struggle to reach 20 degF on Fri-
Sat, which could be near record cold high temps in some locations.
The LREF has a 30-50% chance of wind chills meeting advisory
criteria (colder than 15 degrees below zero) north of I-72 Friday
night into Saturday. While the exact intensity of the cold remains
in question, the CPC 6-10 day and 8-14 day (valid through Dec 19)
outlooks both favor colder than normal temperatures across
Illinois, so our cold start to meteorological winter appears set
to continue.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1112 PM CST Sat Dec 6 2025

Challenging aviation forecast for all sites next 24hrs. VFR
conditions will start all sites, but MVFR cigs will arrive as a
mix of fzdz and snow arrives at most sites. SPI is the only site
that will see only rain through the period when precip is expected.
BMI and PIA will have winter mix of snow, sleet, and freezing rain
overnight, but should transition to a mix of rain and snow toward
morning. DEC and CMI will also see winter mix or fzdz/sn, but
change to ra/sn mix toward morning, followed by drizzle and snow
mix in the morning. IFR cigs/conditions will also arrive over
night with the precip from the west. However, very low cigs and
vis have begun to advect northward from the south and will affect DEC,
CMI and BMI prior to the precip and during the precip. Once
precip ends tomorrow late morning, IFR & LIFR cigs will continue
tomorrow afternoon, but as the front moves through, clouds will
scatter out at PIA and BMI. Scattering out of clouds is possible
at SPI, DEC, and CMI, but confidence is low and would prefer to be
somewhat pessimistic. So, will go with broken MVFR clouds around
2.5kft for the evening hours.

Winds will be southeast at 10kts or less through the night and
tomorrow morning, but when the boundary moves through, winds will
become northerly and be breezy with gusts around 20kft for late
morning through afternoon at all sites. Wind speeds will decrease
during the evening hours.

Auten

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST Sunday for ILZ027>031-
036>038-040>048-053>057-063.

&&

$$