Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

416
FXUS63 KILX 251121
AFDILX

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

.KEY MESSAGES...

- A semi-stationary frontal boundary will meander over central
  Illinois through the remainder of the week resulting in a wide
  range of temps that span from the 40s north of the front to 60s
  south. NBM has 70-90% chance of highs above 55 southeast of the
  IL river from Friday through Sunday, with highs in the mid to
  upper 60s likely in southeast IL Friday and Sunday.

- Fog will be widespread across much of central Illinois near and
  north of a warm front into mid morning and again tonight into
  Friday morning. A Dense Fog Advisory is in effect through 10 am
  across central IL, along and north of I-70.

- Another weak disturbance will return chance of light rain
  showers tonight and possibly lingering in eastern IL Friday
  morning. Precipitation amounts will be light with only a 10-20%
  chance to exceed a tenth inch of rain. A stronger storm system
  moving into IL Sunday will likely bring moderate rainfall along
  with isolated thunderstorms. LREF has a 45-70% chance of
  exceeding half inch rain over CWA Sunday and Sunday evening,
  with highest numbers in southeast IL and lowest nw of IL river.
  Much colder temperatures to usher in early next week with strong
  winds behind the arctic front.

&&

.DISCUSSION...
Issued at 345 AM CST Thu Dec 25 2025

A dense advisory is posted along and north of I-70 through 10 am.
We may need to expand the dense fog advisory to our southern most
5 counties. Latest CAMs also showing improving vsbys over our
northern counties next few hours to may be able to cancel dense
fog advisory sooner especially from Macomb to Bloomington north.

The 09Z/3 am surface map shows weak 1017 mb low pressure over nw
Ohio with a cold front extended sw and approaching I-70 in
southeast/southern IL. The front then arches back into central MO
and southern KS. Widespread dense fog has been over central IL
past several hours north of I-70 with patchy dense fog forming in
southeast IL (Lawrenceville and Olney airports vsbys down to 1/4
mile). CAMs showing dense fog spreading southward next few hours
into southeast IL while decreasing in northern CWA as north to NE
winds increase and bringing in some drier air with dewpoints in
the upper 30s/lower 40s in northern IL, versus mid 40s to lower
50s in central IL and mid to upper 50s in southeast IL.

1030-1032 mb Canadian high pressure over west central Ontario and
eastern Manitoba will track eastward to just south of James Bay
Canada by sunset, while helping push the cold front further south
through southeast IL this morning. Another weak low pressure
system over the Central Plains by this evening to help push the
boundary slowly back northward across southern/sw IL during this
evening and lifting northward over central IL overnight, getting
into northern IL by dawn Fri as low pressure tracks eastward
across northern IL on Fri morning. We should likely see more
widespread fog including dense fog with drizzle develop along and
north of this front this evening and lift northward with the
front during the night. Another dense fog appears likely over much
of central IL tonight, especially north of I-70. Chances of light
rain showers will also increase during this evening with highest
pops north of I-74 where likely pops are tonight.

Fog should gradually lift from sw to ne during Friday morning
along with chances of light rain and drizzle ending by late
morning. Low clouds to give way to skies becoming partly sunny
during Fri afternoon and allowing warmer temperatures. Highs Fri
range from mid to upper 50s northern CWA to upper 60s to near 70F
in southeast IL which will approach record highs. The front to
push back se during Fri afternoon with sw winds shifting west to
nw Fri afternoon with gusts to around 20 mph.

Yet another low pressure system ejects from KS and strengthens as
it lifts ne over northern IL by dawn Sunday. So warm front to lift
back ne over area on Saturday afternoon and evening with south to
SE winds. Highs Sat in the mid to upper 50s from I-74 north and
low to mid 60s south. Models have trended slower with polar cold
front pushing se into central on Sunday and should see moderate
rain showers on Sunday with isolated thunderstorms. LREF has
45-70% chance of over half inch rainfall Sunday and Sunday
evening, highest in southeast IL. Sunday highs reached in the
morning form mid to upper 50s from I-55 nw and mid to upper 60s
in southeast IL. Strong nw winds behind the strong cold front to
have temps tumble later Sunday and Sunday night with rain mixing
with snow by Sunday evening nw of I-70 with some light
accumulations possible over the IL river valley. Lows Sunday night
drop into the teens in central IL (wind chills getting into
single digits below zero nw half of CWA) and lower 20s in
southeast IL. Strong NW winds gusting 25-35 mph into Monday to
usher in polar air mass with highs Monday only in the low to mid
20s, with upper 20s far southeast IL. Lows Mon night in the low to
mid teens and wind chills could dip to around or below zero over
central IL though NW winds will be decreasing during Monday night.


We will be controlled by Canadian high pressure from Monday
through Thu with dry conditions expected along with below normal
temperatures. Highs Wed appear to get closer to normal in the mid
to upper 30s but another cold front slipping southward into IL on
Thu to bring some colder air back into the region.

07

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 521 AM CST Thu Dec 25 2025

Visibilities have been improving the last couple hours north of a
KUIN-KDNV line, with 1/4-1/2SM visibility lingering from KSPI-
KCMI. This will also improve soon, as a frontal boundary shifts
winds to the northeast. Low clouds will be going nowhere though,
with ceilings hanging around 500 feet much of the day. Another
round of fog is expected to develop this evening, with HREF
guidance suggesting around a 40% chance of visibilities below a
mile for about a 3-5 hour period toward and after 06Z. Some
improvement expected late in the period, as the front lifts back
north and winds shift to the south.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST this morning for ILZ038-040-
042>057-061>063-066>068-071>073.

&&

$$