392
FXUS63 KILX 091534
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
934 AM CST Sun Nov 9 2025

.KEY MESSAGES...

- Unsettled, breezy, and unseasonably cold over the next 48 hours.
  Wind chill values Monday morning will be around 10 degrees
  above zero.

- Isolated snow showers could develop this evening (20% chance
  between 6 PM and midnight). Any snow showers that do form could
  result in sharp reductions in visibility.

- A narrow band of lake effect snow is expected across eastern
  Illinois late tonight (near or east of I-57 and mainly north of
  I-74). Minor snow accumulations are possible in Champaign and
  Vermilion counties, with a 20-50% chance for over 1".

&&

.UPDATE...
Issued at 934 AM CST Sun Nov 9 2025

Radar imagery late this morning shows a wintry mix of rain and snow
showers across the area. Scattered, more cellular activity is noted
west of I-55 with a recent road camera showing a light dusting on
grassy, elevated surfaces in Canton. Further east, a more defined
band of lake enhanced snow is occuring near/east of I-57. Visibility
at KCMI dropped as low as 1.5 miles so far this morning, with other
reports of very large snowflakes coming in as far south as Mattoon.
More persistent snow activity is expected to shift east over the
next couple of hours with just a few flurries at times possible
through the afternoon.

An upper low will sink south this evening, bringing a bigger push of
colder air and enough forcing to spark the development of scattered
snow showers once again. Models continue to key in on a robust lake-
effect snow band developing from Chicago southward into east-central
Illinois tonight into Monday morning as the winds over Lake Michigan
turn more north-northeasterly. Accumulating snow from this could
extend as far south as Champaign/Vermilion counties. Determining
just how much snow will be our biggest forecast challenge of the
day.

NMA

&&

.DISCUSSION...
Issued at 257 AM CST Sun Nov 9 2025

An early taste of winter is in store over the next 48 hours. As of
08z/2am Sun, a sfc low was located over central IN, with cold air
advection ongoing across much of the ILX CWA. The expected band of
FGEN has developed and extended from near BMI to the northeast at
2am. Temps are generally in the mid 30s along and east of I-55,
although temps have dropped to 32F beneath the most intense
precip. Even in areas that have sfc wet-bulb values above 32F,
mPING and automated sfc stations have reported snow mixing with
the rain at times. At this point, accums should be limited/minor,
but some webcams across Bloomington-Normal show a dusting as of
230am/0830z. Into Sun AM, the wind direction will favor lake
enhanced snow across eastern IL, so maintained 20-50% PoPs mainly
near/east of I-57. A better chance for lake effect snow occurs Sun
night into Mon (more on this later).

While satellite imagery shows some clearing of the cloud deck
across IA, favored a pessimistic sky forecast for today as both
fcst soundings and the NAM CU rule suggest a broken stratocumulus
deck persisting through the day. Kept a mention of flurries in the
forecast through the day, with the better chances being either
early this morning or during the afternoon hours as an upper level
vort lobe impinges from the northwest.

*** SCATTERED SNOW SHOWERS THIS EVENING ***

Deep, anomalous upper level troughing will be in place over the
Midwest/eastern US through Monday night. Associated with this, a
deep upper low digs towards the ILX CWA this evening (between 6
PM and midnight). Fcst soundings show the PBL maintaining a well-
mixed structure after sunset, with steep lapse rates through the
profile (not a surprise given the very cold temps associated with
the digging upper low). With favorable thermodynamics, the DPVA
associated with this wave could kick off some scattered snow
showers tonight (best chance during the 6 PM to midnight
timeframe). There are questions as to how prevalent the showers
will be, with coverage ranging from no precip to scattered showers
depending on which CAM you choose. If snow showers do develop,
RAP fields hint at some `squall` ingredients being in place: 0-2
km winds in excess of 25 kts (around 30 kts), non-zero
instability, high RH, and favorable theta-e lapse rates. This
means that if these snow showers form (20% chance), they could
produce rapid changes in visibility (down to a half mile) and a
quick dusting that leads to slick roadways.

*** LAKE EFFECT SNOW FOR EASTERN IL TONIGHT ***

A lake effect snow band appears increasingly likely to extend well
south of Lake Michigan late tonight, and could lead to snow
accums as far south as Champaign/Vermilion counties. Southern Lake
Michigan water temps are in the low/mid 50s (degF). Typically,
there needs to be a marine air to 850 mb air temp diff of 13 degF
to support lake effect snow. Forecast 850 mb temps for Sun night
into Monday are around 8 to 10 degF, more than 40 degF colder than
the lake. The colder air extends even further aloft, with 500 mb
temps colder than -40 degC/degF. This results in extreme values of
lake-induced instability, with LI CAPEs of 1500 J/kg. These are
highly favorable conditions for lake effect snow, with NWS Chicago
noting in their discussion yesterday that these are "some of the
most impressive lake effect parameters I have personally noted in
my 15 years at WFO LOT".

Within the ILX CWA, we usually see events where the lake enhances
the potential for snow showers or lingering flurries, but it is
quite rate for true lake-effect, accumulating snow to reach this
far south. That`s exactly what some of the latest models are
suggesting though, and given the extreme parameter space it seems
plausible. Winds over the lake will be northwesterly through the
day Sun, then shift to northeasterly tonight, resulting in a lake
effect snow band oriented near or east of the I-57 corridor
(mainly between midnight and 6 AM Monday). CAMs are varied as to
how far south the snow makes it, with the 09.00z HRRR depicting a
narrow band of 2-4" snow depth in Champaign/Vermilion counties.
The NAMNest shows far lesser accums in those counties. Both of
these CAMs seem to mirror the trends of their parent models.

Ultimately, an advisory level snow (2-4") is in the range of
outcomes for Champaign/Vermilion counties, but being this far
from the lake means that subtle shifts in wind direction could
angle the band away from the lake, or impact its ability to extend
this far south from the lake. Given these uncertainties, a winter
weather advisory was not strongly considered at this time.
Probabilistic guidance from the NBM has a 20-40% chance of 1" of
snow for the cities of Champaign and Danville, increasing quickly
as you go northward (50-60% chance at Hoopeston, 70-90% chance
across Iroquois County). The probability of 2" of snow for the
portions of Champaign/Vermilion counties north of I- 74 is
10-30%. Snow could linger in these areas through mid-morning on
Monday.

*** SEASONABLY HARSH CONDITIONS ***

Below normal temperatures will persist through Monday, with little
change to the temperature/wind chill forecast. Normal high
temperatures are in the mid 50s, but highs will be in the 30s
today and Monday. Brisk northwesterly winds, sustained around 20
mph and gusting to 30 mph, will keep wind chills in the low 20s
during the daytime hours today. As lows fall into the 20s tonight,
wind chill values drop to near 10 degrees Monday morning, with a
30-60% chance for values in the single digits (per the latest
HREF).

*** TURNING WARMER ***

As the upper trough shifts east, and sfc high pressure slides
south, temps will start to rebound by Tues. Out west, a slow-
moving, amplified upper trough builds and gradually moves east
during the work week. By Wed, temps return to near seasonable
values (with highs in the upper 50s). By late week, temps climb
well above normal, with 60s and perhaps even 70s in store for
Friday and next weekend. Record highs are for mid-November are in
the mid/upper 70s.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 515 AM CST Sun Nov 9 2025

An unsettled period with a handful of wintry precip chances. The
first is ongoing pockets of RASN, which could briefly result in
MVFR vis at the I-74 terminals (and KDEC) during the first few
hours of the period. Late this evening (00-08z), isolated SHSN
could result in brief but sharp reductions to visby. Included a
PROB30 group for this, but the chances are closer to 20% than
30%. Finally, near the end of the period (06-12z), a lake effect
snow band is expected to reach KCMI. This could also impact BMI,
but the chances were too low to mention in this TAF. Breezy NW
winds gusting 25-30 kts will persist through the period. Ceilings
are a mix of IFR and MVFR now, with a slow improvement back to
broken VFR ceilings anticipated by midday or early afternoon. The
lake effect snow band expected to impact KCMI is likely to have
MVFR ceilings.

Erwin

&&

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

$$