textproduct: Central Illinois

KEY MESSAGES

- Mostly cloudy and cool weather will prevail the next several days before a pattern change brings unsettled conditions, including the potential for thunderstorms, by the middle of next week.

DISCUSSION

Issued at 115 PM CDT Thu Sep 24 2026

Surface analysis early this afternoon shows an expansive area of high pressure centered over Quebec, stretching west through the Middle Mississippi Valley. The surface high will remain steadily anchored in place through the weekend as a developing nor'easter impacts the Mid-Atlantic and Northeast US. Here locally, east- northeast winds have kept a continuous feed of low stratus trapped beneath a subsidence inversion, holding temperatures several degrees below normal. Aside from occasional breaks in the clouds, mostly cloudy conditions will continue the next few days with little change in the surface flow. Because of this, temperatures will remain cooler through the weekend with highs peaking in the upper 60s to middle 70s.

Further west, an upper trough over the southwest US will lift northeast, weakening as it approaches central US ridging. An associated plume of tropical moisture ahead of this feature currently extends across the Plains states and will gradually shift east through the weekend, entering west-central IL by Friday morning. Despite the lack of large scale forcing, occasional shortwaves in the upper flow will promote isolated to scattered light rain showers west of I-55 through early Sunday. Little to no accumulation will result from these.

By early next week, broad ridging will take shape over the central US as the nor'easter/surface low eventually moves into Newfoundland. A Pacific low will move onshore the coast of California Sunday night/Monday and work into the central US by midweek. Forecast guidance differs on the strength and track of this system with the ECMWF favoring a slower closed wave vs. the GFS's faster open wave. Despite the differences, a wetter and more active weather pattern is favored by the middle to late parts of next week. Although the severe weather threat appears low at this time, the potential for heavy rain does exist.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 650 PM CDT Thu Sep 24 2026

Stratocumulus cloud decks of 3-6k ft early this evening over central IL will likely lower overnight, with MVFR ceilings 2-3k ft more common from 09-15Z mainly from BMI and DEC westward. Ceilings to lift back to VFR late Fri morning or early Fri afternoon, though could linger longer at PIA where we have VCSH starting at 14Z/9 am Fri. East to NE winds to likely stay below 10 kts next 24 hours through 00Z/7 pm Fri as large high pressure over southeast Canada (Quebec and southeast Ontario provinces) ridges into the western Great Lakes including northern IL through Friday.

ILX WATCHES/WARNINGS/ADVISORIES

None.