textproduct: Central Illinois

KEY MESSAGES

- Patchy frost is forecast near and north of I-74 tonight. While the chance is low (20-40%), those with tender vegetation should consider covering their plants to prevent damage.

- Scattered thunderstorms (50-60% chance) are forecast Monday into Tuesday. Confidence is low in whether a severe risk will materialize.

DISCUSSION

Issued at 149 AM CDT Fri May 1 2026

***** COOL AND SHOWERY THROUGH SATURDAY *****

At 145am, RAP mesoanalysis reveals a 8820m 300mb trough centered over Ontario. The axis of a mid level shortwave rotating about this upper trough is located just east of roughly I-55. Consequently, precipitation has come to an end across the western two-thirds of the ILX CWA, but showers linger further east. CAMs suggest this activity will depart into Indiana by 4-5am, and then the area should be dry until mid-late afternoon when the next round of light shower activity approaches from the northwest ahead of another shortwave. Forecast soundings suggest that once again low levels will be fairly dry ahead of these showers, so most of this activity likely won't reach the ground. Even so, most CAMs depict at least spotty, light (less than 0.05") precipitation, with the highest chance (15-20%) for measurable rain across areas near and west of a roughly Galesburg to Olney line.

While showers and cloud cover are forecast to linger through much of the overnight period in south and western parts of the area, light winds may favor patchy frost in the north and northeast counties where HREF/NBM suggest a 20-50% chance low temperatures drop below 36 degrees. This was not enough confidence to issue a Frost Advisory, but subsequent shifts will revisit this; for those with sensitive vegetation in areas near/north of I-74, we'd recommend covering those plants just in case.

***** WARMER, FEW STORMS, EARLY NEXT WEEK *****

The Fujiwara effect between a compact trough diving southeast over the Canadian Prairies and the aforementioned, larger trough situated over Ontario will pull the latter back northward on Sunday. This will allow a return to southwest low-level flow across central Illinois, which spells a (brief) return to warmer weather. It will also allow sufficient moisture and instability for a few showers and storms by Monday. In fact, steep mid level lapse rates from forecast soundings and the presence of a warm front (source of lift and increased shear) nearby may promote sufficient instability for a severe storm or two on Monday; various machine learning programs highlight the area with 5-15% severe weather chances.

***** BELOW NORMAL TEMPS RETURN MID WEEK *****

At some point between Monday night and Wednesday, a cold front is forecast to cross the area, bringing a return to cool conditions and an end to the rain. The NBM gives the area a 30-50% chance that high temperatures fall shy of 60 degrees both Wednesday and Thursday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 655 AM CDT Fri May 1 2026

All sites will be VFR excpet for CMI and BMI that are at IFR right now. But this will improve in a few hours. Then broken cigs will return this afternoon at all sites for the late afternoon into the evening hours. Then scattered clouds return for the rest of the night. Winds will be northwest through the day and then become light and variable this evening.

ILX WATCHES/WARNINGS/ADVISORIES

None.