644
FXUS63 KILX 131850
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
150 PM CDT Sun Sep 13 2026

.KEY MESSAGES...

- Pleasant sleeping weather is expected tonight, with low
  temperatures in the 50s. Some lows near 50 can`t be ruled out
  in a few areas north of I-74.

- A significant temperature range is expected Tuesday through
  Thursday, based on placement of a stationary front. South of
  the front, highs in the mid 90s are likely, while low-mid 80s
  are more common north of it.

- Rainfall will be most widespread north of this front as well.
  Chances of more than an inch of rain range from 50-70% near
  Galesburg and Peoria, to around 20% near I-72. Locally strong
  to severe storms can`t be ruled out on Tuesday as well.

&&

.DISCUSSION...
Issued at 150 PM CDT Sun Sep 13 2026

Short Term (Tonight through Monday Night):

High-based showers and scattered storms currently stretch from
central Lake Michigan into southwest Iowa, associated with a
shortwave moving across the upper Mississippi Valley. Morning
high-res guidance does bring these showers into northern parts
of the forecast area by mid afternoon, primarily north of a
Macomb-Bloomington line. Some erosion is likely by late
afternoon, and these should largely be done by early evening.

Drier air is pushing southward, as high pressure moves in from
the northwest. 1 pm dew points are in the 50s north of I-72, and
these will continue to steadily push southward through tonight,
allowing for pleasant sleeping temperatures in the 50s. In
fact, morning HREF guidance has a 30-50% chance of lows in the
40s from about Galesburg-Bloomington northward. Winds shift
around to the southeast on Monday as the high moves eastward
into Ohio. Some recovery in dew points expected by late
afternoon from Galesburg to Jacksonville, though still a
comfortable day overall with highs in the upper 70s to mid 80s.


Long Term (Tuesday through Sunday):

Main forecast challenges will be in Tuesday-Thursday portion of
the forecast, as a cold front becomes stationary over central
Illinois. Another surge of heat will take place Tuesday with
highs in the 90s over much of the forecast area, lingering south
of the boundary Wednesday-Thursday. Much of the guidance has
this front somewhere between I-72 and I-70, and any waffling of
the front may result in forecast temperature busts. Box and
whiskers plots of the NBM members show about a 10-12 degree
high temperature spread along I-72 for the 25-75th percentiles
Wednesday and Thursday, widening further next weekend as upper
level high pressure builds across the Mississippi Valley.
Potential for a heat advisory on Tuesday will need to be watched
closely, but concerns for clouds/rain Tuesday preclude issuing
one this far in advance.

Periods of showers and thunderstorms will occur during this
same time span, especially near and north of the boundary.
Precipitable water values near the top end of mid-September
climatology continue to result in concerns for heavy rain.
Morning guidance has continued to focus the heaviest rain out
across Iowa and northwest Missouri, with probabilities of more
than 2 inches of rain around 50% as close as Galesburg. Chances
for more than an inch are around 50-70% near Galesburg and
Peoria (per morning NBM), dropping to around 20% near I-72. The
heat on Tuesday should help keep a good part of the day quiet,
though the cap may erode enough by late afternoon to get strong
to locally severe storms going. Latest SPC Day3 outlook has a
level 1 severe risk over most of the area, which seems
reasonable.

Late in the week, as the ridge builds northward, the front will
lift back north with it, with some indications of it returning
later in the weekend. Blended guidance keeps 20-40% PoP`s going
with the uncertainty in timing and placement.


&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1204 PM CDT Sun Sep 13 2026

Diurnal cumulus around 3000 feet has recently developed near
KDEC/KCMI. Can`t rule out a brief period of MVFR ceilings before
cloud heights rise over the next hour or two, but probabilities
are too low (about a 20% chance at both sites, per morning HREF
guidance) to justify a TEMPO mention at this point. Otherwise,
any ceilings over the next 24 hours should mainly be around 8000
feet or higher.

North winds around 10 knots this afternoon will gradually turn
northeast as high pressure builds into northern Illinois. Later
in the period, a switch to the east/southeast will take place
as the high slides toward northern Ohio.

&&

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

&&

$$

KEY MESSAGES...Geelhart
DISCUSSION...Geelhart
AVIATION...Geelhart