733
FXUS63 KILX 010938
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
338 AM CST Mon Dec 1 2025

.KEY MESSAGES...

- A fast-moving storm system will bring another round of snow to
  central Illinois today and tonight. Snow accumulations will
  generally range between 2 and 5 inches. Plan on travel impacts
  this evening into the overnight where the more intense snow
  bands develop.

- Much below normal temperatures will prevail through next
  weekend...with the coldest readings arriving Thursday night when
  12z NBM guidance suggests a 50-70% chance of lows dipping below
  zero along and north of a Macomb to Tuscola line.

&&

.DISCUSSION...(through next Sunday)
Issued at 329 AM CST Mon Dec 1 2025

A broad mid-level trough sweeping across the Upper Midwest
continues to tighten the height gradient over the region, with the
latest QG diagnostics indicating a corridor of pronounced 700-mb
Q-vector convergence centered directly over central and southeast
Illinois between 18z and 06z. This supports a period of enhanced
large-scale ascent, maximized late this afternoon into early
evening. While moisture remains modest, the combination of
synoptic lift and increasing mid-level FGEN (700-600 mb) should be
sufficient to generate moderate to occasionally heavy snowfall,
mainly north of I-70.

The latest 00z HREF/LPMM QPF guidance exhibited a slight shift
southward with the axis of heaviest QPF, and this trend was
reaffirmed by the HRRR/NAMnest guidance, which now focuses the
axis along the I-72/Danville corridor. For this reason, we have
expanded the Winter Weather Advisory further south.

In general, the QPF amounts did not change much, with much of the
region lying somewhere in between 0.1-0.3 inches. Cobb/NAM
mesoscale output continues to suggest a SLR closer to 15:1
throughout the duration of this event. This suggests snowfall
totals in the 2 to 5 inch range. Where the HREF/RRFS LPMM QPF
hints toward 0.4 to 0.5 inches within mesoscale banding, totals
could exceed 6 inches locally.

Confidence is high for an advisory-level snow because the
Q-vector convergence and strengthening FGEN provide a robust
dynamical forcing mechanism. However, actual totals will be
sensitive to the mesoscale placement of banding. A shift of the
band by 30-60 miles changes which counties get the higher totals.

Forecast uncertainty remains an issue for areas near and south of
I-70. Coarser guidance, such as the RAP13 model, suggests a
second band of moderate snowfall could develop across far
southeastern Illinois late tonight. This is associated with an
area of sharpening mid-level FGEN (700-600 mb) and a compact
shortwave pivoting across the Missouri Bootheel, which will
augment forcing. However, the broad synoptic ascent appears weaker
than the initial snow band that moves through central Illinois
earlier in the day.

This uncertainty, which is well-represented in recent CAMs
(Convective-Allowing Models), is why we have paused on extending
the Winter Weather Advisory south of I-70. Since the potential
second push of moderate snow across our southeast counties is not
expected until after 00Z, we have time to monitor the trends and
make adjustments as needed.

Temperatures in central Illinois will oscillate between very cold
and just plain cold this week due to shifting high pressure. A
brief warming trend is forecast for Wednesday afternoon, offering
the best chance for much of the area to finally climb above the
freezing mark. This temporary warm-up is driven by a southwest
wind shift ahead of a weak cold front approaching from the north.

The passage of this front may bring a few snow showers Wednesday
evening, but any accumulation is expected to be limited to a
dusting. Following the front, a period of sharply colder air will
settle in. There is high confidence that overnight lows will dip
into the single digits on both Wednesday and Thursday nights.
While a Cold Weather Advisory is currently unlikely, wind chill
values are still anticipated to fall below zero.

One notable trend in the extended forecast is a southward shift
of the late week winter storm system. It is hard to tell if this
is indeed the trend, or just a one-off with the latest round of
model guidance. Nevertheless, the chance for a 1 inch snowfall
across our area is now limited to a 1 in 7 chance, which is
considerably lower than what we were seeing yesterday.
Consequently, the freezing rain potential also diminished.


MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 940 PM CST Sun Nov 30 2025

A large hole has opened in the MVFR ceilings from KDEC-KCMI.
Unsure how far west this clearing will extend overnight. Areas
that due clear out stand a good chance to see IFR cig/vis
develop, and have added this either as predominant or tempo
conditions at all terminals except KPIA through 13-14z. Main
forecast issue for Monday is an approaching storm system that will
spread accumulating snow over the terminals during the afternoon.
IFR conditions are likely for several hours with snow starting to
taper off toward the end of this TAF period.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon today to 6 AM CST Tuesday for
ILZ027>031-036>038-040>057-061.

&&

$$