textproduct: Central Illinois

KEY MESSAGES

- There is a low to medium (30-50%) chance of light rain Friday into Friday night.

- Dangerous heat builds Sunday through Tuesday, with peak afternoon heat indices of 100 to 110 degrees.

- Isolated severe storms are possible late Sunday through Monday night, though forecast certainty remains low.

DISCUSSION

Issued at 154 PM CDT Thu Jul 23 2026

Surface analysis shows high pressure centered over the lower Great Lakes Region, which has resulted in a brief period of seasonally cool weather. Temperatures early this afternoon are sitting in the middle 70s with dewpoints in the low 50s. Similar conditions are expected on Friday, though southerly return flow will advect moisture back northward later in the day as the surface high pushes off to our east.

An upper shortwave will track from the Central Plains into the Ohio Valley region through Friday night, bringing increased cloudiness beginning tonight. Scattered chances for rain return late Friday morning into Friday night as the shortwave works across southwest parts of the area. Activity will be working against somewhat drier air initially, likely resulting in virga or sprinkles at the onset with total QPF looking to be on the order of a few tenths of an inch. Light rain chances may linger into Saturday morning as a weak shortwave glides along a warm/stationary front positioned just to our south.

Upper ridging becomes amplified over the western US by the weekend, resulting in mid-level height rises here locally. Temperatures will warm back into the 80s on Saturday then surge into the 90s by Sunday. Similar temperatures will stick around through Tuesday for some with the Extreme Forecast Index showing values of 0.9-1, indicating that there is high confidence in an anomalous event. This paired with dewpoints in the 70s will lead to heat indices peaking between 100 and 110 degrees each afternoon. Heat headlines will likely be coordinated in the coming days.

Outside of the heat, isolated chances for severe storms exist late Sunday into Monday night as several shortwave impulses glide along the eastern periphery of a strong upper ridge. A highly unstable and moderately sheared airmass will be in place ahead of the upper waves. If storms manage to initiate, severe hazards and heavy rainfall will be likely. However, forecast certainty remains low until mesoscale features become clearer.

Temperatures will cool back to near typical summertime values behind of cold front by the middle of next week. The CPC 8-14 day outlook favors near to slightly above normal temperatures and below normal precipitation for the end of July/beginning of August.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 601 PM CDT Thu Jul 23 2026

A weather system will bring increasing cloudiness and lowering ceilings through the upcoming 24 hours. Rain is possible, mainly at KSPI after 20Z and PROB30 has been included in the KSPI TAF. Otherwise, VFR conditions are expected to continue for the next 24 hours. Winds E-NE 4-8 kts becoming light and variable this evening. South winds 4-8 kts developing after 15Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.