Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

880
FXUS63 KILX 060933
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
333 AM CST Sat Dec 6 2025

.KEY MESSAGES...

- A Winter Weather Advisory is in effect tonight along and north
  of a Rushville...to Decatur...to Mattoon line for mixed
  precipitation and the potential for a thin glaze of ice.

- Another storm system will bring warmer conditions and mainly
  rain to central Illinois by Tuesday night into Wednesday.

&&

.SHORT TERM... (Today through Sunday)
Issued at 333 AM CST Sat Dec 6 2025

A short-wave trough evident on 0830z/230am water vapor imagery
over Montana will track southeastward over the next 24
hours...spreading wintry precipitation into central Illinois
tonight into Sunday morning. Model consensus suggests precip
developing along/west of the I-55 corridor by late evening, then
spreading eastward across the remainder of the area overnight. The
track of the wave and its associated weak surface low has trended
further north over the past couple model runs...which has shifted
the heaviest precip into northern Illinois and introduced both
moisture and thermal profile uncertainties across the KILX CWA.

Forecast soundings show a shallower moisture profile than previously
thought...with a lack of ice crystals at times along/south of the
low track. This will likely lead to a mixture of light snow and
freezing rain/drizzle rather than all snow.  As WAA increases
ahead of the approaching system, both the NAM and HRRR are
indicating surface temps rising above freezing everywhere south of
the I-74 corridor overnight. Meanwhile the GFS maintains a
slightly colder boundary layer at or a degree or two below
freezing. Given the existing snow cover, am a bit skeptical that
surface temps will reach the middle 30s as the NAM suggests. Even
if the warmer temps verify, pavement temps will be at or below
freezing due to the frozen ground.

Given these parameters, it is becoming increasingly likely that
light freezing rain/drizzle will create a very thin glaze of ice
along and north of a Rushville...to Decatur...to Mattoon line
where a Winter Weather Advisory has been issued. Do not think
there will be significant ice accumulations: however, any amount
of ice will lead to slick driving conditions on untreated
roadways, bridges, and overpasses. Further north where the
moisture profile will be deeper and surface temperatures will stay
colder, more snow will be noted...with accumulations of 1 to 2
inches north of the I-74 corridor. Any wintry precipitation will
come to an end by midday Sunday.

Barnes

.LONG TERM... (Monday through Friday)
Issued at 333 AM CST Sat Dec 6 2025

Cold and dry weather will be the rule on Monday with highs
remaining in the 20s everywhere north of I-70. As southerly flow
increases ahead of the next storm system, readings will rebound
into the upper 30s and lower 40s by Tuesday. As has been seen by
the past several model cycles, the Tuesday system will track well
north of central Illinois...resulting in rain showers Tuesday
night perhaps mixing with a few snow flakes on Wednesday as low
pressure passes into the Great Lakes and winds veer to
northwesterly. After that, forecast confidence is poor for next
Thursday and Friday as models have not yet properly resolved
another potential clipper system dropping southeastward out of
Canada. Current forecast features low chance PoPs (30%) for snow
on Thursday, but this will likely be adjusted over the next few
days.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1003 PM CST Fri Dec 5 2025

MVFR ceilings will overspread the central IL terminals from the
northwest tonight. These ceilings are expected to lower into the
low MVFR range late tonight and Saturday morning, with low-medium
confidence of IFR ceilings developing at KBMI-KDEC-KCMI. Ceilings
are forecast to hold across the region into Saturday night. A
weather system will approach from the west late in the forecast
with -RASN moving into KPIA. Winds southwest to west through the
period under 10 kt.


25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to 6 AM CST
Sunday for ILZ027>031-036>038-040>048-053>057-063.

&&

$$