textproduct: Central Illinois

KEY MESSAGES

- There is an Enhanced Risk (Level 3 of 5) of severe thunderstorms from Champaign to Pana west for late this afternoon and evening. A Slight Risk (Level 2 of 5) extends as far southeast as a Terre Haute to Olney line. Damaging winds, large hail and tornadoes are all possible.

- Low temperatures in the 30s could lead to frost developing both overnight Saturday night and Sunday night. This could harm any sensitive early season vegetation, as the growing season has started across Illinois.

UPDATE

Issued at 949 AM CDT Fri Apr 17 2026

Latest sfc analysis places a cold front from northern MN southwestward into central KS as of 930am/1430z. 12z RAOB from KILX did not have the most impressive profile in the world, with peak mid- level lapse rates of 7.5 degC/km and PWAT values below 0.75". However, upstream RAOBs tell a different story, with the EML evident at KSGF, where 800-600mb lapse rates were very steep, approaching 9 degC/km. In response to the upper trough over the northwest Plains, mid-level SW flow will advect these steeper mid-level lapse rates towards central IL today. Moisture advection will also occur, with PWATs expected to push towards 1.2-1.3", which is above the 95th percentile for this time of year. Not seeing any drastic changes to the severe storm forecast thus far. The 13z SPC Day 1 convective outlook update increased the hail probabilities west of the IL River, and added an intensity level 1 (hail over 2" possible). The intensity level 1 for tornadoes (EF2 possible) was also expanded east to a Taylorville- Champaign line, due to the potential for strong line-embedded tornadoes. Both of these adjustments are well aligned with our local forecast expectations.

Focusing on the next few hours (10am-noon), regional radar shows that scattered showers have developed over SE IL, near the leading edge of the 850mb moisture gradient. These are not expected to become severe, as they are out ahead of the better instability, but did adjust the gridded forecast to add 20% PoPs along and south of a Shelbyville-Paris line this morning.

DISCUSSION

Issued at 400 AM CDT Fri Apr 17 2026

Areas of dense fog over northeast IL from Morris to Kankakee northeast into Lake Michigan will stay northeast of central IL early this morning as breezy south winds develop today with passage of a warm front/trof during this morning. Southerly wind gusts of 25-35 mph likely over central IL this afternoon. This will bring another unseasonably warm and humid summerlike day with highs in the low to mid 80s and dewpoints in the low to mid 60s.

Latest CAMS show isolated showers/thunderstorms developing over parts of east central and southeast IL by midday/early afternoon due to WAA. The main weather story will be strong 994 mb low pressure over south central Nebraska that tracks northeast of Green Bay WI by 06Z/1 am tonight and pulls a strong cold front eastward over the IL river valley. Moderate to strong instability develops ahead of this cold front over eastern/se Iowa and northern MO during early/mid afternoon with SBCAPES above 3000 j/kg while 2-3k J/kg SB Capes over central and western CWA this afternoon west of I-57. Wind shear values peak form 30-40 kts over central IL late afternoon/evening. Initially supercells will likely develop during this afternoon over eastern IA, northern MO into nw IL with a few supercells possible over the IL river valley during mid/late afternoon. These could contain large hail and possible tornadoes with stronger tornadoes EF2 or stronger west of the IL river, with EF3 or stronger nw of Galesburg mainly during late afternoon/early evening. Expect a squall line to eventually develop and track eastward across central IL during this evening with damaging winds becoming the primary threat and could be winds over 75 mph in the enhanced risk area from Champaign to Pana west. The line of storms is forecast to will impact east central/se IL later this evening and early overnight and could still see severe storms. WPC day1 outlook has a slight chance of excessive rainfall over central and nw IL late this afternoon into tonight, with marginal risk of excessive rainfall in southeast IL tonight. Between three quarter and 1 inch of rain expected overall with some areas seeing 1-1.5 inches especially over the IL river valley.

Rain showers and isolated thunderstorms in east central and southeast IL Sat morning, to diminish by midday. Breezy nw winds behind the cold front on Saturday to bring in much cooler air and will likely see temperatures slipping into 30s overnight Sat night with frost likely over central IL by dawn Sunday especially north of I-72. Upper level trof digging into IL Sat night will continue to influence IL on Sunday with cool conditions. Lows again in the 30s Sunday night with frost likely overnight Sunday night over central and ne CWA as Canadian high pressure settles in with lighter winds.

Warmup in store from Monday through mid week as upper level trof shifts into New England and mid Atlantic States on Monday, and upper level ridge building into IL by Thu. Highs in the low to mid 60s Mon climb into the mid to upper 70s Tue and upper 70s/lower 80s Wed/Thu. Precipitation chances look low during early to mid week, with next storms system forecast to push into the Midwest around next Fri/Fri night with better chance of showers and thunderstorms.

The Climate Prediction 6-10 Day Outlook for Apr 22-26 has a 45-55% chance of above normal temperatures over central/se IL and a 40-45% chance of above normal precipitation.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 558 AM CDT Fri Apr 17 2026

Patchy fog at CMI early this morning with vsbys as low as 3/4SM to 2SM since 0930Z is started to lift above 4 miles with increasing high clouds and SE winds up to 7 kts. Have tempo period of MVFR vsby with light fog at CMI until 13Z. Otherwise south to SE winds under 10 kts early this morning to veer south and increase to 16-22 kts with gusts 25-32 kts by late morning and continue through the afternoon. Scattered cumulus clouds with bases 3-5k ft to appear during this morning with broken high clouds. The 09Z HRRR model keeps isolated showers west of PIA and SPI and south of CMI through early afternoon. An approaching strong cold to likely bring a squall line east to PIA around 01Z, to BMI and SPI by 03Z and DEC and CMI between 04-05Z. Have a 2 hour period of WNW winds 35G45 kts with +1TSRA and MVFR ceilings. Showers diminish between 09Z-12Z behind cold front overnight with MVFR ceilings lingering. West to NW winds remain gusty at 20-25 kts overnight into Sat morning.

ILX WATCHES/WARNINGS/ADVISORIES

None.