780
FXUS63 KILX 181743
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1243 PM CDT Fri Sep 18 2026

.KEY MESSAGES...

- Unseasonable Heat & Temperature Contrast: Areas south of the
  front will see heat indices near 100 F through Saturday. This
  is primarily near and south of Interstate 72.

- Thunderstorms & Microburst Risk: Scattered showers and storms
  are forecast through Sunday. On Saturday, stronger storms
  could produce localized damaging wind gusts up to 60 mph and
  quarter-sized hail.

- Significantly Cooler Next Week: High confidence that the hot
  air will be pushed south by Monday. Expect comfortable, dry
  conditions with highs in the upper 60s to mid-70s areawide
  Tuesday through Friday.

&&

.DISCUSSION...
Issued at 1231 PM CDT Fri Sep 18 2026

An anomalous 594-mb heat ridge continues to hold firm over the
central U.S. early this afternoon. Positioned along the northern
periphery of this heat dome, a weak surface low rests near
Sioux City, Iowa, with an associated warm front stretching
southeastward through Columbia, Missouri toward Terre Haute,
Indiana.

As weak shortwave energy ejects out of the Desert Southwest, it
will ride over the frontal boundary, offering sufficient
synoptic lift to drive scattered shower activity today. These
shortwaves will also push the frontal system slightly north
from tonight into Saturday.

Near the warm front, pooling surface dewpoints in the lower 70s
will help support MLCAPE around 2000 J/kg, keeping the
potential for an isolated thunderstorm in place. Poor mid-level
lapse rates will limit any severe threat today. However, as the
front drifts northward on Saturday, increasing bulk shear (2535
kts) may compensate for the weak lapse rates, allowing for
occasionally organized storms capable of producing localized
severe microburst winds and quarter-sized hail. Brief heavy
downpours resulting in 1"/hr rates are a low (10-20%)
probability, but could accompany the more organized convection.
This potential is best highlighted by the HREF LPMM QPF, which
hints at localized amounts up to 1.5".

Beyond the scattered showers and isolated storm potential
through Saturday, the primary forecast difficulty centers on the
sharp temperature contrast across the region. With the boundary
draped across central Illinois, locations to the north will be
capped in the 80s, whereas areas to the south will climb back
into the 90s with heat indices approaching 100 F. Outflow from
passing precipitation could lead to sharp local variations in
temperatures through Saturday.

By Sunday, model guidance and ensemble suites exhibit high
confidence that a closed upper-level trough will track east
across the Plains and into the Mid-Mississippi Valley by Monday.
This system will dismantle the heat ridge and push the frontal
boundary south and east of the forecast area. In its wake,
expansive high pressure will settle in under a blocking split-
flow regime aloft, bringing a period of drier and significantly
cooler conditions. Daytime highs from Tuesday through Friday are
expected to remain in the upper 60s to mid 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1157 AM CDT Fri Sep 18 2026

Broken MVFR to IFR ceilings persist early this afternoon across
KPIA, KBMI, and KCMI, positioned just north of a surface front
situated south of Interstate 72. However, satellite imagery and
recent high-resolution guidance indicate rapid clearing to VFR
conditions over the coming hours as boundary layer mixing
expands.

Ceilings are expected to deteriorate back to MVFR overnight
along the frontal boundary, particularly near the Interstate 74
terminals (KPIA/KBMI/KCMI). Furthermore, a low (2030%) risk of
scattered thunderstorms exists along the front Saturday
morning. To account for this potential, a PROB30 group has been
introduced for TSRA across the I-74 corridor sites.

For the remainder of the TAF period, surface winds will
gradually shift from easterly to southerly as the frontal system
slowly lifts across the region.

&&

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

&&

$$

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