Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

180
FXUS63 KILX 201112
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
612 AM CDT Tue Oct 20 2026

.KEY MESSAGES...

- Dry and mild weather is expected through this weekend along
  with a fair amount of sunshine and fairly light winds. Highs
  will climb into the 70s with lows in the 40s and lower 50s
  today through Sunday.

&&

.DISCUSSION...
Issued at 315 AM CDT Tue Oct 20 2026

Delightful fall weather will likely continue through at least
early next week across central and southeast IL. The 08Z/3 am
surface map shows large 1031 mb high pressure over eastern
Ontario Province and ridging SSW across the Great Lakes region
and IL/IN. Aloft a mid/upper level ridge was over the MS river
valley with cutoff upper level lows/trof off the mid Atlantic
Coast and West Coast/CA. Nighttime Microphysics satellite
imagery shows a swirl of scattered to broken mid/high clouds
over central and southern IL, and more widespread high clouds
in southern/sw IL. Temperatures not as cool as past few nights,
with current mercury levels in the 40s, ranging from 38F at NWS
Lincoln to 51F at the Bloomington airport and 50F at Peoria
airport. Light to calm winds with dewpoints in the low to mid
40s, with a few spots having upper 30s at Lincoln and Lacon.

Surface high pressure strengthens to ~1033 mb as it drifts
eastward into Quebec by sunset while still ridging back over IL
and upper level ridge staying over IL. Strong subsidence over IL
today, with high clouds decreasing during this morning, lasting
longest in southeast IL where partly to mostly cloudy skies
early this morning gives way to sunny skies by late morning.
With dewpoints a bit higher and with light to calm winds and
high clouds decreasing, could see patchy shallow ground fog
early this morning near rivers/creek beds and other water areas
but coverage limited and whatever fog develops will lift quickly
after sunrise. Highs today in the lower 70s with very light
winds with high pressure ridge overhead. Fair tonight with lows
40-45F. Little change with weather on Wed as surface and upper
level ridge stay over IL. Some clouds increasing over the IL
river valley/western CWA on Wed but still a fair amount of
sunshine Wed. Temps 1-2 degrees warmer with highs 70-75F and
very light to calm winds.

Another high pressure drifts eastward across southern Ontario
Wed night and pushes a weakening cold front southward into the
southern Great Lakes by early Thu morning and will have little
affect on our weather with nearby high pressure ridge and light
ne flow developing over CWA on Thu. Ample sunshine Thu with
highs in the low to mid 70s. The large high pressure system
strengthens to 1036 mb or stronger as it moves over PA/NY by
Saturday morning and stays near the mid Atlantic States through
the weekend and surface ridging sw into the lower MS river
valley pinching off gulf moisture from returning to IL.
Circulation around high pressure gives a light se flow on Friday
with sunny skies, and highs in low to mid 70s. Strong mid/upper
level ridge into the Eastern Plains on Friday shifts east into
IL on Saturday ensure dry and mild weather. A bit stronger SSE
winds Saturday and some increasing clouds overnight Fri night
into Saturday as skies become partly cloudy. SW winds on Sunday
with partly sunny skies and highs in the mid to upper 70s.

GFS model is most aggressive with pushing a cold front and some
rain chances se into central IL late Monday afternoon and
Monday night while GEM and Ecmwf models keep CWA dry as system
weakens since moving into strong mid/upper level ridge from the
OH/TN river valleys into the Southeast States. Highs 70-75F over
central/se IL Mon and upper 60s nw of the IL river but if front
is slower to move in would likely be warmer there too. Temps
cool closer to seasonable levels next Tue/Wed.

The Climate Prediction Center (CPC) 6-10 Day Outlook for Oct
25-29th has 50-60% chance of above normal temperatures over IL
and 35-45% chance of below normal precipitation (especially
southeast IL). CPC 8-14 Day Outlook for Oct 27-Nov 2 has 55-60%
chance of above normal temperatures over central/se IL and
35-45% chance of above normal precipitation (especially in
western IL). As of Oct 18th, Illinois has 63% of corn harvested
and 66% of soybeans harvested, running 5% ahead of schedule.
Generally looks like favorable weather conditions into next week
for the 2nd half of harvest season. Given the dry and mild
weather pattern for at least next week, and developing moderate
drought in southeast IL, some fire weather concern with possible
field fires. Though lighter winds and RH`s staying above
critical thresholds should help limit field fires.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 612 AM CDT Tue Oct 20 2026

VFR conditions will prevail at all TAF sites next 24hrs with
few cirrus and clear skies. Winds will remain light and
variable under high pressure.

&&

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

&&

$$

KEY MESSAGES...07
DISCUSSION...07
AVIATION...Auten