textproduct: Central Illinois

KEY MESSAGES

- A storm system will bring showers to central Illinois Wednesday into Thursday. While rainfall will generally remain light, the latest NBM suggests a 30-50% chance of exceeding 0.25, mainly along and northeast of I-74.

- After a stretch of warm weather with temperatures in the 60s, much cooler conditions will arrive for the last part of the week as highs dip into the 40s for Thursday through Saturday.

DISCUSSION

Issued at 1248 PM CST Mon Nov 9 2026

**** Mid-Week Rainfall ****

After a period of quiet weather with high temperatures in the 60s through Tuesday, a storm system will move into the area on Wednesday. All 12z models are in good agreement concerning the strength/timing of the system, with all solutions showing two short-wave troughs phasing into a significant upper trough east of the Mississippi River. All models also suggest the associated precip will not start until after the phasing gets going, which means part of the area will remain mostly dry. The corresponding surface low will track eastward and deepen over central Illinois on Wednesday, leading to the next chance for precipitation. Strong upper dynamics will be in place and the GFS is showing PW values increasing to around 1 inch ahead of the low. Therefore, confidence is growing that showers will become widespread during the afternoon and evening, especially in the northeastern and eastern parts of the CWA. This is reflected with NBM PoPs of 20-40% in the western half of the CWA and 40-60% in the eastern half of the CWA. In addition, a narrow band of instability characterized by MUCAPEs of around 500 J/kg will support the potential for a few rumbles of thunder. Once the low passes to the east, the bulk of the showers will push into the Ohio River Valley Wednesday night. After that, attention will turn to the increasingly cyclonic flow aloft and a band of lake-enhanced showers from Lake Michigan on Thursday. The end result will be a chilly/gloomy day on Thursday with a stiff N/NE breeze and perhaps a few light showers. Storm total rainfall for Wednesday and Thursday has decreased from previous thinking...with the latest NBM indicating only a 30-50% chance of exceeding 0.25, but mainly along and northeast of I-74. This means the remainder of the CWA will either see no precip or much less than one quarter of an inch.

**** End of Week Cool-Down ****

An upper trough is still expected to dig over the Great Lakes/Ohio River Valley by the middle and the end of the week. Colder air will flow southward on the back side of the departing low pressure, and temperatures will temporarily drop below normal for this time this year. The extended models all show 850mb temps dropping to -5 to -8C by Friday. Therefore, after a breezy/chilly day on Thursday with highs in the upper 40s and lower 50s, the coldest day will be Friday when highs only reach the middle 40s. As high pressure builds into the region and winds diminish, the coldest night of the forecast period will arrive Friday night when lows dip into the middle to upper 20s across the board, which should lead to a hard freeze. However, this will be temporary. Once the upper trough shifts eastward and heights begin to rise, temperatures will moderate through the rest of the weekend and into early next week...with readings climbing back to near 60 by next Monday.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1124 AM CST Mon Nov 9 2026

VFR conditions will prevail at all TAF sites next 24hrs with clear skies or a little bit of high cirrus. Winds will be SW the rest of the day and tonight, but then switch to W-NW tomorrow morning as a dry front moves through the area.

ILX WATCHES/WARNINGS/ADVISORIES

None.