080
FXUS63 KILX 281802
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1202 PM CST Fri Nov 28 2025

.KEY MESSAGES...

- Periods of heavy snow will occur on Saturday for portions of
  central and west central Illinois. There is currently a very
  high (80-100%) chance of exceeding 6" of snow along and north of
  a Quincy to Kankakee line, and a high (50-80%) chance of
  exceeding 5" of snow along and north of a Pittsfield to
  Danville line. These hazardous weather conditions will likely
  disrupt travel and commerce. Forecast confidence is lower across
  portions of east central and southeast Illinois where rain may
  mix with snow.

- Unseasonably cold temperatures will accompany a fresh snowpack,
  with overnight lows falling into the single digits both Sunday
  night and Monday night. Wind chill values may approach zero
  wherever there is an appreciable snowpack. Temperatures will
  then remain some 10-15 degF below normal through the middle of
  next week, setting up a prolonged period of cold weather
  impacts.

- Some signal for additional light snow has emerged for later
  Monday into Tuesday. There is currently a low (30-50%) chance of
  exceeding 1" during that timeframe.

&&

.DISCUSSION...
Issued at 436 AM CST Fri Nov 28 2025

Synoptic Pattern:
An area of elongated surface high pressure will continue to build
across the central US today as mid-level heights steadily
increase in the wake of our departed mid-week wind storm.

Further upstream, two notable features can be observed on
satellite this morning. The first is an upper-level trough carving
into the Pacific Northwest. The second is a sub-tropical jet
streak nosing across northern Mexico. Global guidance remains in
firm agreement that these features will phase together over the
Southern Plains overnight, with a moisture-laden, mid-latitude
cyclone pivoting toward the Mid-Mississippi Valley by Saturday.

The expectation is for dry air to quickly erode overnight as
strong warm and moist advection develops north of the surface low,
with upper jet diffluence resulting in an expansive area of
precipitation. Snow will be most likely at the onset with the
thermal profile and surface wet bulb temperature being cold
enough. Then, as the surface low deepens and lifts into central
Illinois by Saturday evening, some transition to a rain-snow mix
will be possible across portions of east central and southeast
Illinois.

Gusty winds (25-35 mph) will accompany this winter storm system at
nearly every turn. This raises some concern not only for blowing
and drifting snow early on in this event, but also sporadic power
outages, particularly across central and west central Illinois
where the heaviest snowfall is favored.


Mesoscale Features:
Heavy banded-snowfall is likely from central Iowa into central
Illinois overnight as loose jet-coupling results in upper-level
divergence and enhanced lift. As the atmosphere responds with
thermally direct ageostrophic circulations, warm air will rapidly
lift over the baroclinic zone displaced to our south. These
coupled circulations will work to strengthen frontogenesis,
enhance isentropic ascent, and saturate the dendritic growth zone,
making them a key driver of mesoscale banding development and
heavy snow potential between Midnight and Noon on Saturday.

A quick glance at model soundings suggests that SLRs may be higher
than 10:1 at onset. This is supported by the increasing potential
for CSI, with steep lapse rates positioned above a saturated DGZ.
Additionally, column temperatures well below freezing will help
limit riming. Furthermore, surface temps in the 20s will reduce
melting at the surface. This all adds up to SLRs above climatology,
perhaps between 12-15:1 at the onset.

The net effect will be a heavy dump of snow before Noon on
Saturday. The latest REFS guidance supports a high (50-80%) chance
for 1"/hr snowfall rates during the morning hours, primarily in
areas north of I-72 and west of I-55, where between 5 and 8 inches
of snow may fall before midday Saturday. Further south and east
of this area, the mesoscale banding potential is less, and
something in the range of 1 and 4 inches is more plausible.


Forecast Uncertainty:
There is still some nagging uncertainty about the exact track of
the surface low into Saturday evening, and this has major
implications on p-type, particularly for east central and
southeast Illinois.

The latest REFS guidance provides a high (60-90%) chance that the
850-mb temperature will warm above 0 degC in all areas east of
the Illinois River Valley and south of I-74 between 3pm-9pm. This
supports at least partial melting of hydrometeors, which will
likely dramatically lower SLRs and take a bite out of additional
snow accumulations. The latest Cobb output suggests SLRs closer
to 6-8:1 by late afternoon and early evening. As sloppy/wet snow
falls atop the fluffy stuff from earlier in the day, compaction
may give the illusion of less snow than what actually fell; just a
word of caution for those not measuring with a snow board.

Another thing weighing down SLRs later Saturday afternoon will be
the wind. As boundary layer winds in the 2-5 kft range increase
to 40-50 kts, dendrites will be more prone to fracture.

Between the uncertainties in exact surface low position and
strength, partial melting, and fracturing snowflakes, we thought
it prudent to keep portions of east central and southeast Illinois
in a Winter Storm Watch for now. We will monitor trends and
adjust accordingly throughout today.


Cold Weather Impacts:
Another area of elongated surface high pressure will build across
the Plains into Sunday and linger into Monday. This cold, dry air
mass will only help to refrigerate our impending snowpack and
help send overnight temperatures into the single digits both
Sunday night and Monday night. Wind chill values may approach zero
each of those nights.

Temperatures will then remain 10-15 degrees below normal through
the middle of next week, giving us a real taste of January.


Additional Light Snow:
Model guidance is now coming into better focus of an additional
snowfall event later Monday into Tuesday. This wave is faster and
less organized than its predecessor, but looks poised to drop
anywhere between a dusting and a couple inches across the region.

MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1202 PM CST Fri Nov 28 2025

Main aviation forecast challenge will be the timing of the
incoming snow and lowered ceilings/visbys. All model guidance
suggests the heaviest snow will hold off until closer to daybreak
Saturday: however, the HRRR continues to show a push of much
lighter snow well ahead of the main precip area during the late
evening into the overnight hours. Have therefore included VCSH at
the terminals starting during the 04z-08z time frame. As the
atmosphere moistens from the top-down, ceilings will lower and
heavier snow will spread into central Illinois from west to east
late tonight into Saturday morning. Based on the latest HRRR/RAP
timing, have introduced MVFR ceilings at KPIA by 09z...at
KBMI/KSPI by 11z, then further east to KCMI by 16z. Given the
strong lift/dynamics associated with the system, think a period of
moderate to heavy snow is likely Saturday morning. Have therefore
lowered ceilings to IFR and visbys to 1/2 mile at the western
terminals after 13z-16z.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from midnight tonight to 6 AM CST Sunday
for ILZ027>031-036>038-040>043-047>053.

Winter Storm Warning from 6 AM Saturday to 6 AM CST Sunday for
ILZ044>046-054>057-061.

Winter Weather Advisory from 6 AM Saturday to 6 AM CST Sunday
for ILZ062-063-066>068-071>073.

&&

$$