Normal, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

776
FXUS63 KILX 252335
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
535 PM CST Thu Dec 25 2025

.KEY MESSAGES...

- A frontal boundary will oscillate across central and southeast
  IL through Saturday, resulting in periods of nighttime fog.
  Visibilities dropping below 1/2 mile at times will require
  motorists to reduce speed and drive with extra vigilance.

- Scattered showers and thunderstorms will shift east across the
  area ahead of a cold front on Sunday. Along that front, we may
  (30-50% chance) see a brief wintry mix, with a few snow showers
  behind it Sunday night into early Monday.

- Expect an abrupt return to winter behind the cold front Sunday
  evening, with northwest winds gusting over 30 mph and
  temperatures plummeting into the teens by early Monday morning.
  This rapid drop in temperatures may result in a flash freeze
  (icy conditions) on untreated sidewalks and roadways.

&&

.DISCUSSION...
Issued at 104 PM CST Thu Dec 25 2025

***** PERIODS OF FOG CONTINUE *****

A stout 500mb ridge remains across the Tennessee Valley and portions
of the Midwest, favoring seasonably mild conditions across central
and southeast IL. At the surface, a quasistationary frontal boundary
has settled across roughly the I-64 corridor. North of that front,
east-northeast winds are advecting a drier and slightly less mild
airmass into central IL, with temperatures currently in the mid
to upper 40s along the I-74 corridor to low-mid 50s along/south of
I-72.

This evening and through tonight, the aforementioned boundary will
lift back northward as a warm front, likely resulting in another
period of fog from 10pm to 4am. Confidence in sub 1/2 mile
visibilities spans at 40-70% across areas north of the I-70
corridor. The transient nature of this fog, with CAMs depicting
around 2-4 hours of poor visibilities at any given location, makes
it difficult to issue a proactive advisory highlighting the
potential. For now, we`re holding off on issuing, but stay tuned
through this evening as we and our neighboring offices reassess
upstream observations and new model data to coordinate potential
headlines.

Weak low pressure developing in southern Iowa tonight will drift
across northern IL Friday morning, dragging a weak cold front west-
east across the area. As a result, temperatures, which will warm
into the upper 50s to low 60s with the warm front overnight east of
the IL River, will slowly drop during the day tomorrow - reaching
the 40s in most locations north of roughly I-70 by 6pm. Making it
feel slightly cooler will be west winds gusting 15-25 mph late
morning through mid afternoon.

Those winds will ease tomorrow night into Saturday morning as
surface high pressure settles into the region behind a reinforcing
cold front. This may result in yet another period of fog or low
ceilings, with the HREF highlighting the highest probabilities (30-
50%) for visibilities under 1/2 mile west of roughly I-55 by 6am
Saturday. At some point Saturday afternoon into Saturday night,
global models suggest the cold front, which will stall across far
southern IL tomorrow night, will lift back northward as a warm
front, with temperatures behind it warming once again into the upper
50s to mid 60s Saturday night into early Sunday morning.

***** SHOWERS AND STORMS SUNDAY *****

Though there`s not a particularly strong disturbance lifting through
the area at the time, global models and their respective ensembles
are hinting we may have several hundred J/kg of elevated CAPE to
support a few thunderstorms by Sunday morning. In fact, the ECMWF
depicts a an EFI of 0.8 to 0.9 and shift of tails for instability,
indicating relatively high confidence in unusually high CAPE for
this time of year, and an at least 10% chance for extreme values
(above the 99th percentile from previous model forecasts for late
December). This instability will linger ahead of the cold front
during the afternoon, but uncertainty in the timing of the front`s
passage lends low confidence in where a possible second round of
storms will fire; chances appear highest east of a Hoopeston to
Shelbyville line where CSU paints a 15% severe risk. We suspect this
may be overdone, but given the 40-55 kt effective bulk shear evident
on soundings even this small amount of instability could favor a
marginally severe storm or two with hail being the main concern.
Beneficial rainfall will accompany Sunday`s showers and storms, with
amounts varying widely from nothing in spots that get entirely
missed (15-30% of our area) to over an inch (20-40% chance east of I-
55) beneath thunderstorms.

Outside of thunderstorms, expect a seasonably warm and humid start
to the day with temperatures in the upper 50s west of the IL River
to mid-upper 60s south of I-70 and dewpoints in the mid 50s to low
60s. Global models still don`t quite agree on the arrival time of
the cold front, though things have generally trended slower over the
past couple days. At this point, the GFS, ECMWF, and their
respective AI versions bring the cold front through the area
sometime between early Sunday afternoon and mid evening. Along that
front, a band of precip starting as rain and transitioning to snow
is depicted in some global models. Forecast soundings suggest a
pretty significant dewpoint depression will materialize beneath the
DGZ as dry air punches into the region along that front, with
graupel looking more likely, but there`s plenty of time to monitor
that.

***** TURNING ABRUPTLY COLDER *****

Behind that front, expect an abrupt drop in temperatures and uptick
in winds out of the northwest. The combination of plummeting
temperatures and evaporational (from pre-frontal rain) cooling of
surfaces may result in a flash freeze on untreated surfaces Sunday
night into Monday. We`ll be interested to see what the CAMs come in
with for wind gusts Sunday night into Monday. Given it`s cold
advection, we wouldn`t be surprised if the PBL remains sufficiently
well mixed for gusts to 40 mph as GFS forecast soundings advertise,
but it`s also during the overnight period so confidence in how gusty
we get is fairly low. More than anything, the combination of
temperatures falling into the teens by Monday morning with winds
gusting at least 30+ mph will make it feel like 5 below to 5 above
0. In fact, with highs in the low-mid 20s and sustained winds of 15
to 20+ (gusts 30+) mph on Monday wind chills are unlikely to climb
out of the single digits. In addition, forecast soundings are
showing steep low level lapse rates, weak instability, and (near)
saturation in the DGZ during the early-mid morning, so we may wind
up with some snow showers during this time as well. Thankfully, the
limited moisture will preclude much in the way of accumulations with
LREF/NBM giving less than a 20% chance for more than a half inch.

Conditions are forecast to turn less cold Tuesday and beyond as the
upper level trough shifts into Quebec and ridging slowly expands
northeastward out of the Plains. Forecast highs generally run in the
mid to upper 30s (near climatological normal) with less than a 20%
chance for precipitation through Thursday, New Years Day.

Bumgardner

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 535 PM CST Thu Dec 25 2025

IFR cigs will likely decrease to LIFR this evening, and a period
of dense fog will likely bring quarter mile/VLIFR vsbys to the
central IL terminals between 01Z-06Z as a warm front lifts across
the area. Improvement in conditions is expected to begin gradually
late in the night, with dense fog shifting north of the area after
around 08Z. MVFR cigs expected by 18Z-21Z along I-74, but as early
as 09Z at KSPI and KDEC. Winds E-SE 7-12 kts, shifting to S by
08Z-12Z and W-NW by 17Z-20Z.

37

&&

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

$$