textproduct: Central Illinois

KEY MESSAGES

- Patchy frost is forecast near and east of I-57 tonight. While the chance is low (20-40%) and frost should be relatively brief, those with tender vegetation should consider covering their plants to prevent damage.

- Scattered showers and thunderstorms are forecast Sunday evening into Wednesday. There is a Marginal Risk of severe thunderstorms Sunday evening for parts of central and southeast IL, and again Monday evening throughout central IL.

DISCUSSION

Issued at 219 PM CDT Sat May 2 2026

A cool air mass lingers over central and southeast IL and should allow for another cool night as diurnal cumulus diminishes and at least a period of clear skies and light winds develops as a shortwave ridge crosses the area. Concerns for frost continue for tonight, however increasing pressure gradients and high clouds ahead of an approaching cold front should limit the duration of strong temperature falls as well as increase near surface mixing late in the night. Have lows of 36 to 38 in southeast/east-central IL, just to the brink of frost formation, and lower 40s from I-72 north where more high clouds and wind are expected. HREF (High Res Ensemble Forecast) system depicts a 30-50% chance of briefly reaching 36 degrees at 6 AM in southeast IL, which isn't quite enough to tip the scales to a frost advisory (would want a few hours worth of frosty conditions and higher probabilities), but will include patchy frost in forecast.

Ahead of the aforementioned cold front Sunday, we could see areas of showers Sunday morning as an upper shortwave traverses the area, mainly north of I-70. By early afternoon, showers should mostly depart, however diurnal heating should eventually allow for a few storms to overcome a cap and realize a few hundred to around 1000 (SW portions of CWA) J/kg. With up to 50 kt sfc-500 mb shear, a few strong to severe storms could eventually form, and SPC depicts a Marginal Risk for severe thunderstorms in Central IL's sw tier of Counties arcing from Scott/Morgan County to Shelby County southward to Clay County. Timing of any severe storms would most likely be around 5 to 10 pm.

The front will stall out and weaken overnight, while the next front approaches from the north, progged to arrive in central IL Monday night. Models depict relatively low coverage of precipitation through Monday afternoon, but increasing coverage should take place in the evening as a low level jet strengthens and the front nears the area. Enough instability, on the order of 1000-1500 J/kg and sfc- 500 mb shear around 40 kts should support a few strong to severe storms. SPC has a Marginal Risk for severe storms across central and southeast IL for Monday evening.

The front looks to linger over the area Tuesday and just south of the area Wednesday as a couple of additional disturbances propagate along the front. Severe weather should be confined to the south by Wednesday, but at least low severe weather probabilities linger into Tuesday. Occasional rainfall can be expected into Wednesday, before the main trough axis shifts east and northwesterly flow and lower chances for precipitation ensue for late in the week into next weekend.

Temperatures will trend strongly upward Sunday into Monday with highs in the upper 60s to lower 70s Sunday and mid to upper 70s Monday before temperatures trend much below normal again Tuesday through Thursday. Upper 50s to 60s can be expected through midweek.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1253 PM CDT Sat May 2 2026

BKN coverage of diurnal cumulus around 6000 ft AGL will continue until this evening, then dissipate as high clouds approach ahead of a weather system that could bring scattered showers around 13Z-18Z Monday. VFR conditions expected through the period, with very low probabilities of below 5 mile vsby or 3000 ft cigs in shra Monday. Winds NW-NE under 10 kts this afternoon, becoming light and variable by 01Z. SW winds increasing overnight and becoming 10-15 kts with gusts 20-25 kts by 15Z.

ILX WATCHES/WARNINGS/ADVISORIES

None.