364
FXUS63 KILX 280746
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
246 AM CDT Mon Sep 28 2026

.KEY MESSAGES...

 - Quiet and Seasonable Early Week: Quiet, mild conditions
   continue through tonight with highs in the mid-70s and lows
   near 50. Warm air pushes afternoon temperatures into the 80s
   for Tuesday and Wednesday.

 - Widespread Rain Thursday into Friday: A slow-moving cold
   front will bring widespread rainfall to central Illinois late
   Wednesday night through Friday.

 - Rainfall Totals and Heavy Rain Potential: Areas north of
   Interstate 70 have a medium (40-60%) chance of receiving over
   1 inch of rain through Friday evening. While the chance for
   over 2 inches is lower (1030%), localized heavy rain bands
   could produce higher amounts.

 - Cooling Down by the Weekend: Cooler, dry air moves in by
   Saturday afternoon, dropping high temperatures into the upper
   60s to close out the week.

&&

.DISCUSSION...
Issued at 245 AM CDT Mon Sep 28 2026

A blocking high anchored over the Great Lakes through tonight
will keep central Illinois quiet under seasonable conditions,
with high temperatures in the mid-70s and lows near 50. The
region remains situated between an upper-level shortwave trough
moving inland from the eastern Pacific and an east coast low off
New England.

By Tuesday, the synoptic setup rapidly changes as the western
trough absorbs the remnants of Tropical Depression Polo.
Shortwave energy downstream will eject across the Plains into
the Mid- and Upper-Mississippi Valleys, pushing the east coast
low out to sea and dismantling the blocking ridge. Associated
thermal and moisture advection will drive afternoon temperatures
into the 80s for Tuesday and Wednesday.

Recent model guidance has pushed back precipitation timing.
Trends show the parent trough phasing with Polo and forming a
closed upper low. This will hold the surface cold front to our
northwest, delaying rainfall chances across central Illinois
until early Thursday morning.

While some uncertainty remains concerning the cutoff low, model
guidance consistently shows it opening up and tracking eastward
along the slow-moving cold front by Friday. High confidence
exists for widespread rainfall from Thursday through Friday;
however, exact accumulation totals and localized mesoscale
banding will depend on the timing and sharpness of the front.
Both blended and ensemble guidance suggest a 4060% probability
of rainfall exceeding 1 inch north of Interstate 70 through
Friday evening. The likelihood of total accumulations exceeding
2 inches is lower (1030%), though localized mesoscale banding
could still produce these higher amounts.

Although low precipitation chances persist through midday
Saturday to account for a potential delay in the northern stream
shortwave and frontal boundary, conditions are expected to dry
out as Continental Polar (cP) high pressure rapidly expands
across the Midwest and Great Lakes region. This airmass shift
will usher in a distinct cooling trend relative to mid-week
temperatures, holding daily highs in the upper 60s as the week
draws to a close. Extended guidance suggests this high-pressure
system will remain entrenched through midweek, maintaining a
stretch of ideal autumn weather.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1147 PM CDT Sun Sep 27 2026

VFR with SCT high clouds through Monday. There is a low chance
(30%) of lowered visibilities in fog early this morning,
particularly at KCMI.  Winds continue light northeast.

&&

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

&&

$$

KEY MESSAGES...MJA
DISCUSSION...MJA
AVIATION...25