Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

901
FXUS63 KILX 150526
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1226 AM CDT Wed Oct 15 2025

.KEY MESSAGES...

- The risk for strong to severe thunderstorms, including damaging
  winds, will increase late Friday night into Saturday. The SPC
  has issued a 15% probability for severe weather along and south
  of the I-72 corridor.

- Isolated pockets of heavy rainfall will be possible Saturday,
  with localized totals exceeding 2 inches where slow-moving
  storms develop and train. The overall chance for heavy rain is
  approximately 10-15 percent.

&&

.DISCUSSION...
Issued at 138 PM CDT Tue Oct 14 2025

High pressure is centered over the Canadian Prairies and Upper
Midwest this afternoon and is progged to inch eastward across the
Great Lakes through Friday. Aloft, a blocky upper level ridge is
centered along the Great Plains while an attendant mid-level
thermal ridge also remains just off to our west. Precip chances
through the remainder of the work week will generally be off to
our west and northwest along the nose of the thermal ridge driven
by mid level warm air advection, through there is an off chance
(10%) that some of these showers could drift east or southeast
along the periphery of the ridge into portions of central/north
central Illinois, especially Wednesday and Thursday mornings.

The upper ridge axis is set to shift east across central Illinois
Friday. This will favor dry weather continuing and temperatures
should peak under the ridge with afternoon highs near 80F.
Meanwhile, a deep upper low over the Desert Southwest today is
expected to lift to the northern Great Plains Thursday night into
Friday with a surface low deepening in response. The surface low
will lift to Hudson Bay over the weekend with a trailing cold
front pushing across central Illinois Friday night into Saturday.
Timing remains a bit uncertain, and slower guidance (ECMWF)
suggests that moderate instability will build across central
Illinois within the warm sector Saturday afternoon. Dew points
pooling in the low to mid 60s ahead of the front will contribute
to SBCAPE of 700-1000 J/kg within a strongly sheared environment
(0-6km shear vectors in excess of 50kt). If we are able to realize
this instability, then a severe threat may materialize with
frontal passage. The SPC 15% contour for severe weather Saturday
comes up to roughly the I-72 corridor. In addition to the severe
threat, 850-300mb flow runs largely parallel to the slow moving
surface cold front which would be favorable for training of
thunderstorms. NBM mean QPF for a 48-hour window ending Sunday
morning runs roughly half to three quarters of an inch for the
entire area. 90th percentile QPF shows a few pockets over 2
inches, and given the training potential, expect that there will
be isolated swaths of heavier rain where 2+ inches occurs.

Following the weekend system, temperatures will cool back to near
the seasonal norms, with highs on Sunday and Monday peaking in
the 60s to around 70 degrees. Additional chances for rain return
around the middle of next week as another area of low pressure
lifts across the region.

Deubelbeiss

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1221 AM CDT Wed Oct 15 2025

A weak mid level disturbance interacting with a stationary frontal
boundary across central IL has resulted in numerous clouds between
FL050-FL120, and even some sprinkles near and north of roughly
I-80. A couple models suggest this precip activity may approach
BMI or CMI between mid morning and early afternoon, but given low
confidence (15% chance) and the lack of potential impacts opted to
leave this out of the TAFs. VFR conditions are expected (90%
chance) to prevail through 06z/1am Thursday, with northeast winds
running 5-10 kt.

Bumgardner

&&

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

$$