375
FXUS63 KILX 292351
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
651 PM CDT Thu Oct 29 2026

.KEY MESSAGES...

- Beneficial rain showers will return Friday afternoon through
  the weekend as an active weather pattern sets up. Isolated
  pockets of 0.50 to 1.00 inch of rain are possible, though most
  areas will see under half an inch.

- Mild temperatures in the 70s and periodic rain chances will
  continue through midweek next week. A sharp cooldown arrives
  late next week, dropping high temperatures into the 40s and
  50s.

&&

.DISCUSSION...
Issued at 100 PM CDT Thu Oct 29 2026

Near Term (Rest of Today into Tonight)...
Our prolonged period of dry weather will become more active in
the days ahead as a series of disturbances cross the region.
First in the series is a weak cold front currently bisecting the
ILX forecast area, stretching roughly from Bloomington to
Jacksonville early this afternoon. Very modest instability is in
place ahead of the boundary, with short term RAP forecasts
indicating around 300-500 J/kg MLCAPE superimposed beneath weak
deep-layer shear of 20-25 kt. While parameter space is
unfavorable for organized severe weather, an isolated
thunderstorm or two remains possible into early evening. Overall
precip coverage will remain isolated (15-20%) given weak low-
level convergence along the tail end of the cold front. Rainfall
will focus primarily along and southeast of the BMI to IJX
line. HREF LPMM guidance indicates localized rainfall amounts of
0.25 to 0.33 inches in stronger convective cores, though most
locations will receive little to no measurable rain. Coverage
will wane rapidly around sunset with the loss of diurnal
heating.

The frontal passage will establish a sharp north-to-south
temperature gradient today and Friday. Highs north of the
boundary will top out in the upper 60s to lower 70s, while
locations to the south warm into the upper 70s to around 80
degrees.

Short Term (Friday through Weekend)...
A surface ridge axis shifts into the Great Lakes tonight,
allowing low-level return flow to develop from the west across
central Illinois by Friday afternoon. Isentropic upglide and
mid-level warm air advection will generate shower and
thunderstorm activity over the Great Plains on Friday, with
steering flow carrying remnants into west-central Illinois
Friday afternoon and eastern Illinois Friday evening. Weak
elevated instability rooted near 850 mb will support shallow
convection; however, poor mid-level lapse rates will keep
equilibrium levels near or below the ice-growth zone,
suppressing lightning potential. HREF LPMM shows the potential
for localized rainfall swaths of 0.50 to 1.00 inch, especially
across west-central Illinois.

Broad isentropic ascent across the 300-310K surfaces will
expand east across the Mississippi Valley over the weekend,
bringing additional rain showers. Weak mid-level lapse rates
(<6.0 C/km) will continue to limit thunderstorm activity, but
moisture transport will push precipitable water (PWAT) values up
to 1.00-1.25 inches by Sunday afternoon exceeding the 90th
percentile of GEFS model climatology. NBM 24-hour QPF mean
values average around 0.10 inches through Saturday night,
increasing to 0.10-0.25 inches Sunday and Sunday night. NBM 90th
percentile suggests isolated pockets exceeding 0.5-1.0 inch
will be possible primarily across east-central and southeast
Illinois. Given the antecedent dry conditions, rainfall will be
beneficial with negligible impacts.

Long Term (Monday through Wednesday)...
A closed upper-level low over the West Coast will dig
southeastward into the Central Plains on Monday, inducing
surface cyclogenesis over Colorado and Kansas. The upper low is
projected to stall and slowly meander eastward across the
mid/lower Mississippi Valley through midweek. While timing
differences between the models persist, mild temperatures in
the 70s and periodic shower/thunderstorm chances will dominate
early to midweek. A strong cold front trailing the surface low
late in the week will usher in a significantly cooler airmass,
dropping high temperatures into the 40s and 50s. Given timing
discrepancies among models, the NBM currently broad-brushes the
thermal gradient late in the week averaging out the forecast
highs in the 60s.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 651 PM CDT Thu Oct 29 2026

23z/6pm surface analysis shows a slow-moving cold front dropping
southward toward the I-70 corridor. Any isolated showers
associated with the boundary will remain well south of the
central Illinois terminals through the rest of the evening.
While skies have cleared at both KPIA and KBMI, a band of broken
cloud cover at 5000-7000ft persists at the I-72 sites. Based on
satellite trends and HRRR/NAM forecast soundings, it appears
these clouds will scatter after 02/03z. The front will stall
across southern Illinois tonight, then will begin lifting back
northward as a warm front on Friday. All models develop
showers/thunder across Missouri into southern Iowa late tonight
into Friday morning:however, the eastward extent of the precip
remains in question. Some CAMs such as the HRRR are fairly
aggressive with the eastward push of showers as early as
morning...while others like the RRFS are slower and tend to
dissipate the showers as they try to spread into the area. Given
the consistent dry E/NE boundary layer flow north of the warm
front and very dry soundings below 5000ft, am inclined to side
with the drier RRFS. As such, have limited PROB30 for showers to
just KPIA and KSPI between 18z Fri and 00z Sat.

&&

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

&&

$$

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