Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

244
FXUS63 KILX 051752
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1252 PM CDT Sun Apr 5 2026

.KEY MESSAGES...

- Freezing conditions will occur across north-central Illinois
  Monday night. There is a 60-80% chance readings will drop
  below 30 degrees along and north of a Macomb...to Lincoln...to
  Paris line.

- Warmer and wetter weather will return by the end of the week.

&&

.DISCUSSION...
Issued at 317 AM CDT Sun Apr 5 2026

Partly to mostly cloudy skies will prevail along and northeast
of a Peoria to Mattoon line at daybreak: however, this cloud
cover will gradually shift eastward out of the area this
afternoon. Despite increasing amounts of sunshine, brisk
northwesterly winds gusting 15-25mph will keep temperatures
several degrees below normal in the middle 50s.

A cold front currently over the Northern Plains will drop
southward through the region tonight. The boundary will have
very little moisture to work with, so am only expecting an
increase in cloud cover and a shift in the wind with FROPA.
Northwesterly breezes behind the front will ensure another cool
day on Monday with highs once again hovering in the lower to
middle 50s.

As Canadian high pressure settles southward into the Upper
Midwest and winds decrease, a very chilly night will unfold
Monday night. Previous thinking suggested all of central and
southeast Illinois would be in for a freeze: however, the last
few model runs have introduced a fly-in-the-ointment that will
likely keep temps a bit warmer across the S/SW KILX CWA. A band
of frontogenetic forcing most evident in the 800-700mb layer
will develop from eastern Nebraska to southern Illinois late
Monday afternoon into Monday night. While the airmass will
initially be quite dry, weak isentropic upglide and low
condensation pressure deficits on the 300k surface will lead to
a band of cloud cover and perhaps light precipitation. The 00z
Apr 5 NAM/GFS/ECMWF all hint that the best chance of measurable
precip will remain further west across northern
Missouri/southern Iowa: however, plenty of clouds will develop
further E/SE into parts of central Illinois. In addition, with
the surface ridge axis extending from Minnesota southeastward to
Ohio, am expecting NE winds of 5-10mph to persist through the
night. The combination of cloud cover and wind will prevent a
widespread freeze. Based on the expected parameters, think the
I-74 corridor will be the most likely location to experience a
hard freeze. As such, the latest LREF highlights locations
along/northeast of a Macomb...to Lincoln...to Paris line with a
60-80% chance of dropping below 30 degrees by dawn Tuesday.

After a chilly day with highs only in the middle to upper 40s on
Tuesday, southerly return flow will develop on the back side of
the departing high and temperatures will quickly moderate by
the middle and end of the week. Highs will return to the upper
60s to around 70 degrees by Wednesday, then will climb well
into the 70s Thursday through Saturday. Along with the warmer
weather, showers and a few thunderstorms will return to the
forecast. The severe weather risk will remain low through the
end of the week, but may increase by next Saturday/Sunday as
moisture becomes more prevalent and a stronger system arrives.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1251 PM CDT Sun Apr 5 2026

A weak upper level disturbance is expected to dig across
northern  Illinois this evening and overnight. Across central
Illinois northwest winds currently in place are expected to back
to the southwest this evening ahead of the feature, then veer
to the northwest again overnight in its wake. VFR conditions are
expected through the period.

&&

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

&&

$$

KEY MESSAGES...Barnes
DISCUSSION...Barnes
AVIATION...Deubelbeiss