Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

999
FXUS63 KILX 211105
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
505 AM CST Sun Dec 21 2025

.KEY MESSAGES...

- Seasonable temperatures today are forecast to warm well above
  normal into mid week across central and southeast IL, and remain
  above normal through at least Saturday. There is a 40-80% chance
  (per NBM guidance) of temperatures reaching 65 degrees or
  warmer on Christmas Day along and southwest of a Macomb to
  Lincoln to Terre Haute line.

- There`s a 20-50% chance of light showers in southeast IL Monday
  night. There is a 20-30% chance of light showers across much of
  the area Wednesday afternoon and Wed night along with some
  drizzle into early Thu morning. Rainfall amounts should stay
  less than a tenth inch if they occur.


&&

.DISCUSSION...
Issued at 330 AM CST Sun Dec 21 2025

The 09Z/3 am surface analysis shows 1027-1029 mb Canadian high
pressure over central Iowa and north central MO and ridging into
sw/southern IL. NW winds 5-10 mph have brought in cooler
subfreezing temperatures back into the area, with temps in the
mid 20s to lower 30s, with lower 20s at Galesburg and Macomb.
Band of mid/high clouds was southeast of a Danville to Taylorville
line while a smaller band of mid/high clouds was streaming
eastward across northern MO into west central IL. A semi-zonal
mid/upper level flow prevailed across much of the country with an
upper level trof near the Quebec/Ontario province line and into
the Great Lakes region. A subtropical ridge (500 mb heights of
585-588 dm) was over Mexico and Baja of California.

High pressure is forecast to strengthen to 1030-1032 mb by midday
as it drifts over IL then 1033-1035 mb during this evening as it
settles eastward over the Ohio river valley. Mid/high clouds to
decrease over southeast IL during this morning while mainly just
some passing cirrus clouds over sw CWA today. So a fair amount of
sunshine and lighter winds generally under 10 mph. Seasonable
temperatures today with highs in the mid to upper 30s (coolest
from I-74 ne) in central IL and lower 40s in southeast IL from
I-70 south and over west central IL from Jacksonville west/sw.
Mid/high clouds to increase later this evening and overnight
especially northern CWA. Lows this evening of 22-28F (coolest east
central IL) to slowly increase to around 30/lower 30s by daybreak
Monday as SSE winds gradually increase.

Large high pressure will be over the mid Atlantic States Monday
while weak low pressure moves eastward across northern Nebraska,
lifting a warm front ne into northeast MO and sw IL by sunset
Monday. A weak disturbance lifting up the lower MS river valley
and into the lower Ohio river valley by Mon evening, to bring
slight chance of light rain showers to se IL Mon afternoon and
20-50% chance of light showers to southeast IL Monday night from
Danville to Effingham southeast. Rainfall amounts should stay
under a tenth inch if they occur. Breezy southerly winds gusting
20-25 mph on Monday with milder highs in the mid to upper 40s,
with southeast IL around 50F with a fair amount of low cloud cover
spreading into CWA during Monday morning.

Isolated light showers could linger in far southeast IL early Tue
morning, otherwise Tue is looking like a nice day with more
sunshine and lighter winds expected along with warmer
temperatures as strong mid/upper level ridge starts to build into
the eastern plains and MS river valley Monday night/Tue. A weak
cold front to push se through central IL Tue afternoon and into
southeast IL Tue evening but should pass through dry with limited
moisture and CAA. Highs Tue range from upper 40s/lower 50s
northern CWA to upper 50s to around 60F in southeast IL. This will
be the start of well above normal temperatures expected the rest
of the week.

A warm front to lift back northeast over central IL Wed afternoon
and evening and combined with a weak short wave ridging top of
upper level ridge into central/northern IL Wed afternoon and Wed
night to bring chance of light rain showers. More low clouds
expected Wed into Thu morning and could see some drizzle too.
Temps on Wed will be dependent on movement of warm front and
likely late day highs with mid 50s from I-74 ne and 60-65F from
Springfield to Paris south. Warm front should pass ne of IL by
daybreak Thu with Christmas Day likely enjoying record warmth with
highs in the 60s and even approaching 70F in southeast IL and sw
of Springfield. Low pressure to pass north of area Thu night and
bring a cold front southward into central IL overnight Thu night
into Fri along with low chances of rain showers Thu night, with
highest chances to our northeast. Some cooling Fri/Sat though
models have trended a bit milder with latest runs as mid/upper
level ridge holds longer over the area. Highs could still reach
the 50s over much of area Fri/Sat, even lower 60s in southeast IL
Friday. A deeper upper level trof and storm system to move into
the eastern US next Sunday/Mon (Dec 28-29) and likely brings
colder temperatures and possible chance of precipitation.

Climate Prediction Center (CPC) 6-10 Day Outlook for Dec 26-30th
has a 70-80% chance of above normal temperatures over central/se
IL and near normal precipitation. CPC 8-14 Day Outlook for Dec
28-Jan 3 continues trend of above normal temperatures (60-70%)
with near normal precipitation central IL and 33-40% above normal
precipitation in southern/southeast IL.

07

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 505 AM CST Sun Dec 21 2025

VFR conditions will prevail the next 24 hours, with mainly periods
of high-based clouds. Winds will become light and variable this
morning as high pressure drifts overhead, before becoming more
southeasterly and increasing again by evening. Some potential for
LLWS late in the TAF period near KPIA, though core of the jet
looks to stay just west of there at this point.

Geelhart

&&

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

$$