Area Forecast Discussion

KEY MESSAGES

- Scattered thunderstorms are possible through this evening north of Interstate 72. A few storms could become strong, posing a risk for heavy rain and damaging winds.

- An upper system slowly lifting through the Midwest states will bring widely scattered showers and storms Sunday through Monday. There is a 40 to 60% chance for total rainfall to exceed 1 inch.

- A stronger warming trend arrives Tuesday through the end of the week, pushing heat index values near 100 degrees.

DISCUSSION

Issued at 154 PM CDT Sat Jun 6 2026

Water vapor imagery early this afternoon shows a 500 mb shortwave ridge approaching from the southwest with a closed low spinning over the southern Plains. Surface analysis has a cold front draped over northern Illinois with steady west-southwest winds in place south of there across central Illinois. Temperatures as of 1 pm have climbed into the middle to upper 80s with dewpoints in the upper 60s to low 70s, and feel-like temperatures in the low 90s. A couple lingering outflow boundaries from overnight storms are evident over northern and central parts of the state and will be the focus for thunderstorm development north of I-72 through this evening. SPC mesoanalysis shows strong instability (2-3k J/kg) and very steep low-level lapse rates (7-8 C/km) in place. Weak wind shear and lack of large-scale ascent should limit overall storm organization, but collapsing updrafts could generate locally gusty winds that may come close to severe limits. Climatologically high PWATs, deep warm cloud depths, and somewhat slow storm motions could also support locally heavy rainfall especially if storms repeat over the same areas. The 12Z HREF 24 hour LPMM shows isolated pockets of QPF exceeding 2 inches near the I-74 corridor through this evening.

Upper ridging gets pushed east of here by Sunday as the previously mentioned closed upper low becomes an open trough and lifts into the Midwest states. The surface cold front will approach our northern counties by Sunday morning, becoming stationary before lifting north of here Monday. Several shortwave impulses embedded within the main trough will promote widely scattered showers and storms Sunday through Monday. Although the threat for severe weather appears low, beneficial heavy rain appears increasingly likely with high PWATs in place. There is currently a 40-60% chance of exceeding 1 inch of rainfall across the entire area with lower chances for exceeding 2 inches. WPC has a slight risk of excessive rainfall in parts of the area both Sunday and Monday for the outside chance of localized flooding.

Mid-level heights rise heading into midweek as upper ridging builds over the east-central US, bringing a stretch of hot and humid conditions. Air temperatures look to climb into the upper 80s to low 90s Tuesday through the end of the week, with heat indices approaching 100 degrees. The LREF (ENS, GEFS, GEPS) shows a 20% chance for heat indices to exceed 100 degrees during this period. Long range guidance depicts an upper trough breaking down the ridge and sending a cold front through the area late in the week or early next weekend, though timing remains highly uncertain. If this moves through sooner than later, a shorter period of prolonged heat would be favored due to increasing precipitation chances with the frontal passage.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1241 PM CDT Sat Jun 6 2026

MVFR ceilings in spots to start the period should lift here shortly, with VFR conditions largely expected the remainder of the period. A couple periods of showers and storms may impact the terminals this afternoon (KPIA, KBMI, KCMI) and Sunday morning. Confidence in timing and exact placement of storms remains low, so PROB30 groups remain in place to cover this probability. West-southwest winds with speeds between 10-15 kts will become light tonight as they back to the south-southeast by morning.

ILX WATCHES / WARNINGS / ADVISORIES

None.