textproduct: Central Illinois

KEY MESSAGES

- Scattered showers and a few thunderstorms are possible this afternoon and evening. Locally gusty winds over 30 mph are possible near showers and storms.

- Patchy frost is possible late tonight into Saturday morning, primarily for areas north of I-74. Additional patchy frost can't be ruled out for early Sunday morning in portions of east-central Illinois.

- Isolated strong to severe thunderstorms are possible Sunday afternoon and evening. The main concerns would be locally damaging winds and hail. Additional strong to severe storms can't be ruled out for Monday as well.

DISCUSSION

Issued at 211 PM CDT Fri May 1 2026

*** Short Term (This afternoon through Saturday) ***

The synoptic pattern remains dominated by an expansive long-wave trough centered over the Great Lakes and Southeast Canada. Several shortwaves continue to rotate through this flow, with the next impulse progged to arrive this afternoon and evening. Forecast soundings reveal a notably dry boundary layer with dewpoints in the 30s; however, steep low-level lapse rates will compensate for the lack of deep moisture. Mesoscale models suggest SBCAPE values topping out between 100-200 J/kg with equilibrium levels near 600 mb. This instability is sufficient to support scattered showers and a few embedded thunderstorms, though the meager CAPE and lack of significant shear in this layer will preclude any severe threat. Evaporative cooling could yield localized wind gusts exceeding 30 mph with any convection. PoPs are around 30% for this feature.

By Saturday morning, the primary concern shifts to frost potential. While lows will dip into the upper 30s to lower 40s, lingering cloud cover should limit temperature falls for much of the area. The best chance for patchy frost will be relegated to the far northern counties, specifically north of the I-74 corridor, where clearing is most likely. Saturday will be a cool, brisk day with highs struggling to reach the upper 50s under continued cyclonic flow.

*** Sunday-Tuesday (Frontal Passage & Severe Wx Potential) ***

A transition to a more active and warmer regime begins Sunday as a cold front approaches from the northwest. Return flow will boost highs into the upper 60s to lower 70s. While Sunday morning could see some patchy frost in east-central Illinois, increasing southerly winds and thickening cirrus should mitigate widespread frost development. By Sunday afternoon, ensemble probabilities for SBCAPE>500 J/kg and 06 km Bulk Shear >30 kts are nearing 50%. This environment has prompted a Marginal Risk (Level 1 of 5) from the SPC for much of Central Illinois, as isolated severe thunderstorms cannot be ruled out. PoPs reach 20-40 percent by Sunday evening.

The front is expected to stall or move sluggishly across the region Monday into Tuesday as the eastern CONUS trough deepens. Monday appears to be the warmest day of the period, with highs reaching the mid-to-upper 70s. Despite the SPC currently carrying sub-15% severe thunderstorm probabilities, CSU Machine Learning guidance shows over 5% probabilities for severe weather. Given the forcing and favorable parameter space, Monday will need to be monitored for a severe thunderstorm threat. PoPs peak at 50-60 percent Monday night.

By Tuesday, the front should be suppressed into southern Illinois. While the severe threat will likely shift south of the CWA, high PoPs (50-70%) remain for the area as cyclonic flow and a shortwave are progged, bringing widespread rainfall. Highs should trend down, and are currently forecast in the 60s.

*** Midweek Outlook ***

Turning cooler in the wake of the front on Wednesday. Highs will retreat back into the 60s, with some locations potentially staying in the upper 50s. Cyclonic flow continues, keeping the door open for scattered light showers (PoPs 20-40%). Main trough axis moves east Thursday into Friday limiting chances for precipitation to 20 percent or less, but below normal temperatures continue.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 612 PM CDT Fri May 1 2026

VFR conditions continue. An upper wave will promote scattered showers for a couple hours this evening, ending between 02-04Z. North-northwest winds will be in place to start the period then will turn light and variable overnight. Winds return to the northwest by late morning with speeds around 10 kts or less.

ILX WATCHES/WARNINGS/ADVISORIES

None.