textproduct: Central Illinois

KEY MESSAGES

- A late season heat wave is forecast to impact central and southeast IL much of this week. Afternoon heat indices are projected to reach upper 90s to around 100 Monday, 100-105F Tuesday through Friday, and peaking during mid week around Wed.

- Precipitation chances are low for the next several days, as an active storm track is forecast just to our north through mid week. Isolated showers and thunderstorms are possible over the IL river valley today, especially this morning. There is a 20-30% chances of showers and thunderstorms Friday into Saturday.

DISCUSSION

Issued at 345 AM CDT Sun Aug 30 2026

The 08Z/3 am surface map shows 1022-1024 mb high pressure across the mid Atlantic States and ridging into the mid MS river valley. 1002 mb low pressure was over central SD with a frontal boundary extending eastward over far southern MN into southern WI. South to SSE winds was starting to bring in warmer air into central/se IL. Temps were in the mid 60s to lower 70s with mildest readings from I-55 west. Dewpoints were in the low to mid 60s. Patches of mid level clouds were over central IL and more widespread over IL river valley and ne CWA. A 40-50kt sw low level jet from OK Panhandle ne across central parts of KS and Iowa into southern WI was aiding in development of convection over northern IL into southeast WI, far eastern Iowa and central/southern lower MI. Isolated light showers/sprinkles were over the IL river valley with a heavier shower over far ne tip of Vermilion county east of Hoopeston.

Strong mid/upper level ridge over the Southern Plains and mid/lower MS river valley to nose into central IL during today as 500 mb heights rise to 592-594 decameters by sunset. Latest CAMs show isolated convection over the IL river valley and north of I-74 today, mainly this morning. More widespread convection to be over northern/ne IL today. Most areas should continue to be dry today. Increasing SSW winds to 10-15 mph and gusts 18-24 mph to bring warmer temperatures into the area, with highs in the lower 90s, except upper 80s in cloudier areas from I-74 ne. Mild lows overnight around 70F in eastern IL and lower 70s from I-55 west.

Strong 500 mb ridge builds further north into IL on Mon as 500 mb heights rise to 594-595 decameters and continues holding firmly in place Tue/Wed, keeping ring of fire of storms generally north of central IL. This will also bring hotter temperatures into the area with highs Mon in the low to mid 90s and afternoon heat indices in the upper 90s to around 100F. Highs Tue-Thu in the mid to upper 90s with areas from Springfield to Robinson sw approaching 100F. Heat indices Tue afternoon of 100-105, approaching 105 Wed afternoon and 100-105 Thu and Fri afternoon. The long duration of anomalously warm temperatures for early Sep and lack of overnight relief with lows in the 70s starts pushing the area into Major (Level 3 of 4) to Extreme (Level 4 of 4) Heat Risk Tue-Fri, and remains elevated as the holiday weekend begins. Heat advisories will likely be needed Tuesday through Friday for much of the area especially if the stronger upper level ridge holds over the area.

Medium range models continue to retrograde the strong mid/upper level ridge west/sw with IL getting into a nw upper level flow late this week. Frontal boundary staying north of IL much of this week, could start dropping southward into ne IL late this week, and bring low convection chances into central IL Fri- Saturday. Temperatures trending a bit lower late this week with highs Friday low to mid 90s, upper 80s/lower 90s Saturday and and Sunday. These temperatures are still above normal highs in the low to mid 80s for early Sep.

The Climate Prediction Center (CPC) 8-14 Day Outlook for Sep 6-12th has 55-65% chance of above normal temperatures with 33-40% chance of below normal precipitation over central and southeast IL and near normal over nw/northern IL. So the very warm and drier wx pattern looks to continue next two weeks.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 627 AM CDT Sun Aug 30 2026

VFR conditions will prevail at all sites next 24hrs. Broken clouds will be present this morning and through the afternoon hours, but then these clouds should dissipate early this evening. Scattered showers will move across CMI this morning so have added a TEMPO group for them, though not expecting reduction in vis or cig. Another line of showers and storms has developed northwest of the IL river and am expecting this to hold together for a time this morning and afternoon. Have added VCSH for all sites for late morning through afternoon, but no restrictions in vis or cig expected. Winds will be southerly with gusts around 20kts from late morning through afternoon.

ILX WATCHES/WARNINGS/ADVISORIES

None.