textproduct: Central Illinois

KEY MESSAGES

- Areas of fog early this morning from Peoria to Lincoln to Robinson northeast will be locally dense especially from Bloomington to Paris northeast.

- Oppressive heat and humidity continue through early evening with heat indices peaking between 105 and 115 degrees and a few spots higher this afternoon.

- Multiple thunderstorm complexes will move across IL into this evening, presenting a conditional threat for severe weather. Damaging winds and heavy rains are a risk especially early this morning in southeast IL, and across central and southeast IL this afternoon and early evening.

- A cold front will bring relief from the high heat and humidity on Tuesday, transitioning us back to near normal temperatures and humidity levels during mid week.

DISCUSSION

Issued at 345 AM CDT Mon Jul 27 2026

We have expanded the extreme heat warning over rest of central IL except having Vermilion, Edgar and Clark counties in a heat advisory until 9 pm today. Heat indices this afternoon and early evening to peak from 105-115 with a few spots getting to 120 or higher.

Areas of fog have developed past few hours from Peoria to Lincoln and Decatur to Robinson northeast, with dense fog recently forming at Bloomington and Danville. A dense fog advisory until 8 am from Livingston and LaSalle counties north. The fog should lift and push northeast of central IL between 7-8 am.

MCS over western parts of TN/KY has a tail of convection extending northward into southeast IL (eastern Shelby, western Cumberland, Effingham, Clay and western Jasper counties). Flash Flood warning for eastern Effingham county until 5 am and for southern Clay county until 6 am. A personal weather station on north side of Effingham measured 3.6 inches of rain at 315 am and wind gust 40 mph. Very high PWATs were 1.9-2.25 inches from Decatur SSE and cells moving SSE but backbuilding to the north toward DEC airport. This boundary extends northward into DeWitt and western McLean county so may see some cells develop here too early this morning. CAMs not handling this convection the best though ARW is closer to reality and also Canadian REG latching on to this convection longer. So this narrow band of convection may last a few more hours until 13Z/8 am over parts of east central and especially southeast IL with heavy rain and frequent lightning the main threats. Though a few stronger cells could have wind gusts over 40 mph.

MLCAPEs currently 2500-4000 j/kg and MUCAPES are 4000-5000 j/kg over central/IL with a cap in place at dawn. This very unstable air mass to likely continue through the afternoon when CAPES likely top 4000 j/kg and effective bulk shear values of 30-40 kts. Challenging forecast today with convection chances since triggers are not very obvious. Consensus of models was showing MCS developing over WI this morning and moving southward over central IL during this afternoon/early evening. Though this convection has been slower to develop in east central WI. SPC Day1 outlook has upgraded to a slight risk over central and sw CWA and enhanced risk over ne CWA this afternoon/early evening. There is 15-30% risk of damaging winds, with a level 1 for winds of over 75 mph over much of CWA. There is a 2% to less than 5% risk of tornadoes over CWA. The enhanced risk in ne CWA has 5-15% risk of large hail.

Highs today in the low to mid 90s combined with dewpoints in the upper 70s/lower 80s to give afternoon heat indices of 110-115 and few places reaching 120 or higher. Dewpoints got into the mid 80s late yesterday afternoon at SPI and Macomb with Springfield 84 degrees setting a new record high dewpoint. We expanded the extreme heat warning across rest of central IL except have heat advisory for Vermilion, Edgar and Clark counties until 9 pm. If thunderstorms materialize and move in during the afternoon and early evening, it would cool temps/heat indices and would likely end the heat headlines earlier than 9 pm.

Main synoptic cold front to push southward across central IL overnight and could produce isolated convection with better chances east of IL where better forcing expected. Muggy lows tonight in the low to mid 70s, warmest in southeast IL. Modest northerly breezes on Tue bring in cooler and gradually less humid air as dewpoints slip into the upper 60s/lower 70s Tue afternoon. Highs Tue in the mid to upper 80s with heat indices Tue afternoon peaking in the mid to upper 80s from Springfield and Robinson sw. Quiet weather expected during mid week (Tue- Thu) as weak high pressure ridge settles into IL on Wed with more comfortable temperatures and humidity levels. Highs in the low to mid 80s Wed and mid 80s Thu with lows in the low to mid 60s Tue and Wed nights.

Medium range models show a northern stream short wave trof moving into IL on Friday into Saturday likely bringing next chance of showers and thunderstorms. Highs in the low to mid 80s Fri/Sat and mid 80s Sunday.

The Climate Prediction Center (CPC) 8-14 Day Outlook for Aug 3-9th has 50-60% chance of above normal temperatures over central and southern IL (45-50% chance above normal temps in northern IL) with precipitation trending near normal across IL.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 622 AM CDT Mon Jul 27 2026

Area of IFR ceilings/visibilities extends from KBMI-KCMI early this morning, though it will continue to lift over the next hour or two. Main forecast challenge will be with timing of additional storms. Upstream storm evolution (or lack thereof) introduces great uncertainty with timing, aside from storms currently nearby to KCMI. Will mention PROB30 groups at all sites from 21-24z. Late in the period, winds shift to the northwest and north as a cold front pushes through the area.

ILX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 9 PM CDT this evening for ILZ027>031-036>038-040>045-047>056-061-062-066>068-071>073. Heat Advisory until 9 PM CDT this evening for ILZ046-057-063.