860
FXUS63 KILX 012026
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
226 PM CST Mon Dec 1 2025

.KEY MESSAGES...

- A Winter Weather Advisory is in effect for all of central and
  southeast Illinois through tonight. Snowfall everywhere north of
  the I-70 corridor will range from 2 to 4 inches...with locations
  further south picking up 1 to 2 inches.

- Much below normal temperatures will prevail through next
  weekend...with the coldest readings arriving Thursday night when
  12z NBM guidance suggests a 60-80% chance of lows dipping below
  zero along and north of a Rushville to Mattoon line.

&&

.SHORT TERM... (Tonight through Tuesday)
Issued at 226 PM CST Mon Dec 1 2025

The light snow event has commenced across central Illinois...with
20z/2pm radar imagery and area obs indicating snow reaching the
I-57 corridor. As a short-wave trough currently over the Plains
approaches, synoptic lift will increase and the snow will become
moderate in intensity for several hours. The initial band of
700-800mb frontogenetic forcing has shifted a bit further south
than originally thought...resulting in accumulating snow beginning
along a Jacksonville to Mattoon corridor a couple hours earlier
than locations from Bloomington to Champaign northward. As a
result, have made some minor adjustments to the accumulation
forecast. Still think all locations along/north of the I-70
corridor will see a general 2 to 4 inches, but there could be
isolated amounts up to 5 inches along the Jacksonville to Mattoon
corridor. Further south, it will take a bit longer for the snow to
start, so am expecting 1 to 2 inches south of I-70. Due to the
expected impact to the evening commute, have extended the Winter
Weather Advisory to include the entire KILX CWA. The Advisory ends
at 12z/6am Tue: however, the snow will end long before that. Based
on the consistent HRRR/RAP signal, it appears snow will taper off
and end in the Illinois River Valley after 8pm...then further east
to the Indiana border shortly after midnight.

While winds will veer to the NW and high pressure will build into
the region behind the area of elevated forcing, skies will remain
cloudy overnight into Tuesday. GFS guidance suggests skies may
partially clear during the day: however, both NAM and RAP forecast
soundings show boundary layer moisture becoming trapped beneath a
strengthening subsidence inversion. Given the time of year and the
fact that there will be no strong CAA inflow from the NW, think
the cloudier solution is correct. As a result, have lowered high
temperatures into the lower to middle 20s due to the cloud cover
over the fresh snow cover.

Barnes

.LONG TERM... (Wednesday through Next Monday)
Issued at 226 PM CST Mon Dec 1 2025

Wednesday appears to be the warmest day of the forecast period as
boundary layer winds become southwesterly ahead of an approaching
cold front. Thickness values support a warm-up well into the 40s:
however, the snow cover and continued cloud cover across much of
the area will curtail the warming. Am still expecting highs to
rise above freezing and lead to some melting of the recent snow.
As the front nears, all models are showing scattered snow-showers
northwest of the I-55 corridor by late Wednesday afternoon, then
further east across the remainder of the area during the evening.
Little to no snow accumulation is expected. Once the front passes,
windy and sharply colder conditions will arrive for Thursday. The
good news is that the sun will finally return at that time, the
bad news is that strong CAA will keep daytime highs in the teens
north of I-70 and the lower to middle 20s to the south. The
coldest period continues to look like Thursday night as winds
diminish over the snow cover. 12z NBM guidance indicates a 60-80%
chance of lows dipping below zero along and north of a Rushville
to Mattoon line.

The southern stream storm system that the models had previously
spread into Illinois by the end of the week has now shifted
southward. Given the presence of the Arctic airmass, the more
southern position of the prevailing baroclinic zone and storm
track makes sense. As such, have removed Friday PoPs...except for
just a slight chance (20%) south of I-70. As high pressure shifts
to the east and boundary layer flow once again shifts to southerly
ahead of the next approaching cold front, temps will briefly
rebound into the lower to middle 30s on Saturday. After that,
cold and dry conditions with highs in the upper 20s and lower 30s
is anticipated for next Sunday and Monday.

Barnes

&&

.AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1157 AM CST Mon Dec 1 2025

1730z/1130am radar mosaic and regional observations indicate snow
has spread as far east as the Mississippi River. Further east
across central Illinois, ceilings have temporarily improved to
VFR. Based on radar trends and HRRR/RAP timing, have introduced
light snow and lowered ceilings to MVFR at KPIA/KSPI by
19z...then further east to KCMI by 21z. About an hour after the
snow commences, think ceilings/visby will lower to IFR at all
sites through mid-evening. CAMs have been consistently showing the
snow ending from west to east across the area toward midnight, so
have removed snow and raised visbys back up to 6 miles or more at
KPIA by 03z...then to KCMI by 07z. Despite an end to the precip,
forecast soundings suggest IFR ceilings will persist into Tuesday
morning before slowly improving to MVFR toward midday. Winds will
initially be E/SE at less than 10kt, then will veer to W/NW at
10kt or less late tonight into Tuesday.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM CST Tuesday for ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

$$