Area Forecast Discussion

KEY MESSAGES

- Pleasant Mid-Week Weather: Expect calm weather with below- normal temperatures Wednesday and Thursday, with afternoon highs remaining in the mid-to-upper 70s.

- Heat Returns This Weekend: High temperatures rebound into the 90s by Sunday and Monday. There is a 20% chance of periodic thunderstorms returning late Friday into early next week.

DISCUSSION

Issued at 1219 PM CDT Tue Jul 21 2026

Near Term Forecast... The current surface analysis places a cold front along the I-70 corridor, with expected progression southeastward and out of our CWA by mid-afternoon. RAP analysis continues to highlight an unstable airmass ahead of the boundary, characterized by MLCAPE values near 3000 J/kg and deep-layer shear profiles of 30-40 kt. Given this overlap, a brief window of opportunity for severe thunderstorm development exists through mid afternoon before the front exits the region. Behind the boundary, a cooler and drier air mass is filtering into the region on gusty northwest winds. Dew points have already begun a downward trend, eventually bottoming out in the 50s across the northern tier of the forecast area tonight, with ambient temperatures settling into the 60s under mostly clear skies.

Wednesday through Friday... The middle of the week will feature a transition to a more tranquil regime as a robust Canadian high-pressure system builds southeast across the Midwest. This will facilitate a trend toward below-normal temperatures, with afternoon highs confined to the mid to upper 70s. Dry conditions are anticipated to prevail through Thursday night. By Friday, guidance suggests the potential for warm air advection-driven convection originating to our west. While confidence remains low, there is a non-zero potential for these showers and thunderstorms to encroach upon portions of central Illinois; however, the lack of significant moisture return currently limits more robust PoP inclusion.

This Weekend into Next Week... As the surface ridge translates toward the Atlantic Coast over the weekend, the return of low-level southerly flow will initiate a noticeable warming trend. Temperatures are progged to rebound significantly, with widespread 90s returning to the forecast by Sunday and Monday. The synoptic pattern remains anchored by northwest flow aloft, with periodic, lower-amplitude shortwaves expected to traverse the region. These disturbances may serve as catalysts for convective initiation, though timing and placement remain difficult to resolve this far out. Have capped precipitation chances at approximately 20% during this timeframe until better agreement is reached among short-range guidance.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 607 PM CDT Tue Jul 21 2026

After the smoke and haze of the last couple days, VFR conditions will prevail the next 24 hours, with good visibility. Scattered diurnal clouds will fade with sunset, though a feed of moisture off Lake Michigan will keep a scattered deck near 4-5kt over eastern Illinois. Gusty northwest winds will subside a bit and trend toward the northeast late this evening, with the lake breeze persisting into late Wednesday morning.

ILX WATCHES / WARNINGS / ADVISORIES

None.