textproduct: Central Illinois

KEY MESSAGES

- Another round of mild weather will start the work week, with high temperatures in the 60s Monday through Wednesday.

- The highest chances of any precipitation will be Wednesday afternoon (as high as 60% near and north of I-74), though odds of seeing more than a quarter inch of rain are only around 20-30%.

- Significantly cooler weather is expected late week, with a 60-80% chance of high temperatures below 45 degrees on Friday.

DISCUSSION

Issued at 105 PM CST Sun Nov 8 2026

Short Term (through Tuesday):

Midday surface map shows a weak front approaching the Illinois River valley. Not much to note with this feature, aside from a wind shift to the northwest, with just a few high clouds streaming south well ahead of the boundary. During the early part of the forecast, this trend will continue, despite another weak boundary arriving Monday night. Temperatures Monday and Tuesday will reach the 60s, with some potential for nudging 70 degrees in areas south of I-70 on Tuesday.

Long Term (Wednesday through Sunday):

Main forecast concerns for this cycle are in the long term, regarding rain chances mid week and temperatures late week.

Morning synoptic models continue to develop a shortwave trough over the Pacific Northwest Monday night, deepening over the central Plains Tuesday night. Getting past Wednesday, additional waves will drop southward out of Ontario, resulting in a sprawling upper low dominating the eastern CONUS by Friday. This will provide the region with significantly cooler air, with LREF guidance highlighting a 40-50% chance of highs below 45 degrees near/north of I-74 Thursday, and 60-80% chance in most areas north of I-70 Friday. NBM temperatures toward the end of the period (next weekend) were lowered due to biases near the Great Lakes, though the morning GFS ensembles suggest some temperature recovery by Sunday just to our northwest.

Regarding precipitation trends, chances continue to increase Wednesday (now about 60% near/north of I-74) as the shortwave digs over Iowa/Missouri. Much of this will fall during the afternoon. A few hundred joules of CAPE may be enough to trigger a few rumbles of thunder as well. With this storm system intensifying in the general vicinity on Thursday, some lingering showers are most likely over eastern Illinois. Getting into Thursday night, surface flow becomes more oriented off Lake Michigan, with a mixture of rain and snow showers downstream over northeast Illinois and northwest Indiana. Depending on the ultimate wind orientation off the lake, a few of these may sneak into east central Illinois near Danville late Thursday night or early Friday morning. This threat should become more focused over Indiana later Friday, as a ridge of high pressure edges into the mid-Mississippi Valley.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1122 AM CST Sun Nov 8 2026

Breezy conditions will continue through the afternoon, with 10-15 knot winds gradually switching from southwest to northwest with the passage of a weak front. Winds will diminish near or shortly after sunset, gradually becoming southwest late in the period.

Little in the way of cloud cover is expected through much of the period. Some of the model guidance has been hinting at some ground fog early Monday morning, though NBM probabilities of MVFR-level visibilities are currently only 20% at all the terminals.

ILX WATCHES/WARNINGS/ADVISORIES

None.