textproduct: Central Illinois

KEY MESSAGES

- Warmer conditions with gradually increasing moisture are anticipated for the remainder of this week, with a 10-30% chance of rainfall greater than 1" in the Friday-Saturday time frame, which is the most likely period for precipitation. Severe weather potential appears low.

- Cooler conditions become increasingly likely for Sunday, with a 30-50% chance of high temperatures below 80 degrees along with more comfortable humidity. Some chance of rain continues, particularly south of I-72/Danville.

- Look for warmth and moisture to return early next week, with a 20-40% chance of heat indices above 95 degrees. Low chances of daily rainfall greater than 0.5" exist, increasing to around 30% on Wednesday.

DISCUSSION

Issued at 334 AM CDT Wed Jun 11 2025

Though the air quality index due to wildfire smoke remains in the moderate category at most monitoring stations across central Illinois, impacts appear to be diminishing with only a couple of stations reporting minimal visibility restrictions over the last few hours. The greater driver for visibility restrictions through mid-morning may be the near-saturated low-level conditions along with calm winds near and south of I-70. Patchy fog has been added to the forecast. So far, the closest observing site to our forecast area to detect fog has been Mount Vernon along I-64.

Southwest winds will develop across central Illinois during the day today, helping to further clear the wildfire smoke and also bringing warmer temperatures along with gradually increasing moisture. This evening, a cold front is forecast to stall somewhere near the IL/WI state line, with any associated overnight precipitation remaining north of this front. Outflow from this evening's/Thursday morning's convection largely across WI could push an effective boundary a bit into northern Illinois, likely remaining north of the ILX forecast area.

A closed low over west TX this morning will gradually make its way toward central Illinois as an open wave trough by Saturday morning. Ahead of this feature, precipitation chances will begin to increase somewhat on Thursday, but will be highest on Friday and Saturday. Increasing moisture will supply some instability with CAPE profiles largely of the "long skinny" variety, but with fairly minimal deep layer shear severe storm potential is anticipated to be low. Precipitable water values climb into the 1.5-2 inch range on Friday and Saturday, so any storms that do develop in this environment could be efficient precipitation producers. WPC currently has us in a marginal risk for excessive rainfall on Friday roughly east of I-55. Looking at the period as a whole, the chances of rainfall greater than 1" over the 48 hour period ending 7 am Sunday range from about 10% northwest of Peoria to 20-30% south of I-70.

Deterministic models show somewhat cooler and drier air filtering into central Illinois on Saturday night in the wake of the surface low associated with the aforementioned short wave trough. There are some differences with regard to the magnitude and southward extent of this cool-down that will affect high temperatures on Sunday. For the moment, NBM probabilities of Sunday's max temperature being below 80 degrees are around 30-50%. Some rain chances persist, most notably south of I-72/Danville. For early next week, there is quite a bit of model variability in how rapidly a ridge builds over the Plains, and in how strong/what trajectory various short wave troughs follow that could bring us precipitation chances. 24 hour probabilities of precipitation greater than 0.5" hover around 10-20% for the Sunday-Tuesday period, increasing to around 30% on Wednesday. The most likely maximum heat index values in the Monday-Wednesday time frame will be in the low 90s, with a 20-40% chance of exceeding 95 degrees.

AAT

AVIATION

(For the 06z TAFs through 06z Wednesday Night) Issued at 1208 AM CDT Wed Jun 11 2025

VFR conditions are expected through Wednesday night. Light southwest winds overnight will pick up some during the day, then turn light Wednesday night as they back to the south. Skies will be mostly clear with just a few passing cirrus at times, especially by later in the period.

NMA

ILX WATCHES/WARNINGS/ADVISORIES

None.