116
NOUS43 KILX 181614
PNSILX
ILZ027>031-036>038-040>057-061>063-066>068-071>073-190414-

Public Information Statement
National Weather Service Lincoln IL
1114 AM 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. Locations to the north will stay cooler in the 80s, though localized rain can cause sharp temperature swings.
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

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 moves out of the Desert Southwest, it will lift over the frontal boundary, offering sufficient synoptic lift to drive scattered shower activity today. This wave 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.

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.

$$