Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

258
FXUS63 KILX 242345
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
645 PM CDT Sun May 24 2026

.KEY MESSAGES...

- After lingering showers depart eastern Illinois this
  afternoon, the next chance of rain will be Tuesday night into
  Wednesday. There is a 50-70% chance of rain south of
  I-72/Danville, and a 30-50% chance to the north. Temperatures
  will generally be above normal this week, with highs in the
  low to mid 80s.

&&

.DISCUSSION...
Issued at 119 PM CDT Sun May 24 2026

*** THROUGH TONIGHT ***

A weak cold front has pushed into Indiana as of late Sun
morning, but lingering scattered showers continue in areas east
of a Rantoul to Shelbyville line as of 1230pm/1730z. Shower
activity was more widespread and persistent earlier this
morning, with locally heavy amounts exceeding 1" in some spots
near the I-55 corridor (north of Lincoln). The remaining precip
activity is less expansive in coverage, and also more
progressive as the associated system steadily shifts east. Thus,
additional rainfall amounts seem unlikely to exceed 0.25" this
afternoon, and this notion is supported by the morning HREF
guidance. Latest observations show minimal lightning activity
with the showers across eastern IL, but with MUCAPEs around 500
J/kg, a few rumbles of thunder can`t be ruled out this
afternoon. Precip should depart SE IL before sunset.

The only other forecast concern for tonight is the potential for
fog development as weak sfc high pressure settles in, skies
clear, and residual moisture persists in the low-levels. Latest
high-res guidance did not change the footprint of the fog signal
from previous forecasts, highlighting areas south of
I-72/Danville and east of Decatur as being the most likely
location for vis below 1 mile (20-30% chance). Given some of the
heavier rains closer to I- 55, would not be surprised if the
fog extended a bit further northwest than guidance is showing.

*** THIS WEEK ***

The upper pattern will be blocky this week, with a central US
ridge gradually amplifying as an upper low becomes cut-off over
the western US. The northeast will also feature troughing to
some degree, setting up an Omega block of sorts that keeps the
pattern slow to evolve this week.

Dry conditions are expected on Mon into Tues, as the frontal
zone settles to the south of the ILX CWA. There is a weak upper
disturbance present over the southern Plains currently, which
guidance shows lifting towards the MO Bootheel by Tues eve. This
will help tug the front northward, providing a rain chance Tues
night into Wed, with chances higher south of I-72/Danville
(50-70%) than to the north (30-50%). With both weak instability
(MUCAPE less than 500 J/kg) and weak mid-level flow (500mb winds
less than 25 kts), the prospects of severe storms is very low.
PWAT values are progged to exceed 1.5", and forecast
soundings/hodographs show a deep warm cloud layer (greater than
10kft) with cloud layer winds around 15 kts. This suggests at
least some potential for slow- moving, efficient rainfall
producing showers/storms. For comparison, today`s showers that
produced localized 1-2" totals were working with lower PWATs
(1.2-1.5") and shallower warm cloud depths (less than 10 kft).
For now, the coarser resolution global ensembles are not bullish
about the heavy rain potential, showing just a 20-30% chance of
over 1" south of I-70 through Thurs AM, with lower probs north
of I-70. As a high-res guidance will likely provide a better
idea of the localized, high-end rainfall amounts that could
occur with this system.

For the latter half of the work week, sfc high pressure shifts
south over the Great Lakes, helping to nudge the frontal
boundary back to the south and introducing persistent E/NE flow
that should advect drier air into the region. While the NBM
keeps some broad (20-40%) PoPs in place across the SW half of
the ILX CWA Thurs and Fri, precip chances on Thurs-Fri will be
higher to the south/west of our area, maximized across far
southern IL and into MO. The exact placement and strength of the
high pressure system will impact just how much rain, if any, we
see locally.

With upper ridging in place over the central CONUS for much of
the week, temperatures will be running a bit above normal
locally, with highs generally in the low to mid 80s.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 645 PM CDT Sun May 24 2026

There is a low-medium probability if MVFR fog over eastern IL
late tonight. This could impact KCMI, so went with a TEMPO for
5SM there. Otherwise, VFR conditions will dominate the terminals
through Tuesday. Light north/northeast winds this evening will
veer southeast on Monday near/under 10 kt.

&&

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

&&

$$

KEY MESSAGES...Erwin
DISCUSSION...Erwin
AVIATION...25