textproduct: Central Illinois

KEY MESSAGES

- There is a 50-80% chance southwest winds gust over 35 mph today near and east of the I-55 corridor, promoting patchy blowing dust especially in areas that have recently missed the rains. This can result in localized, sharply reduced visibilities for motorists.

- Isolated to scattered showers and thunderstorms are forecast through the afternoon, and become more widespread tonight. There is slight to marginal risk for large hail and damaging wind gusts, mainly during the 7 pm to 1 am timeframe. The higher risk of severe storms tonight (slight risk with level 2 of 5) is from Canton to Decatur to Taylorville southwest.

UPDATE

Issued at 1045 AM CDT Mon May 4 2026

Updated the forecast to adjust chances of showers and thunderstorms the rest of today. Continued Blowing Dust Advisory from 11 am to 6 pm southeast of the IL river and north of Effingham, Cumberland and Clark counties. SW winds 10-20 mph and gusts of 20-30 mph to increase this afternoon with gusts 30-40 mph possible especially over east central IL per latest HRRR 10M wind gust forecast. This could lead to blowing dust in recently tilled fields between the IL river and I-70, especially in areas that stayed dry so far since last night.

Radar mosaic shows a band of showers and thunderstorms from Springfield to Decatur to Paris south to near I-70 and tracking eastward quickly at 50 mph. There is a subtle short wave tracking quickly eastward with this convection along with 30-40 kt sw low level jet into central IL. This convection should weaken next few hours as LLJ weakens and short wave moves into Indiana. However more convection expected to develop late this afternoon and early evening mainly se of I-55, and also during this evening over nw CWA as cold front moves into nw IL during this evening. SPC Day1 outlook continues marginal risk of severe storms for large hail and damaging winds over much of IL for mainly late afternoon and evening hours, with areas from Canton to Decatur to Taylorville sw upgraded to a slight risk of severe storms. Breezy sw winds and some sunshine to warm temperatures to 75-80F degrees.

DISCUSSION

Issued at 246 AM CDT Mon May 4 2026

***** BREEZY AND WARM WITH PATCHY BLOWING DUST TODAY *****

At 230am, scattered thunderstorms were ongoing across areas near and south of a roughly Jacksonville to Paris line where 30-40 kt effective bulk shear and 250-500 J/kg MUCAPE rooted around 850mb were apparent on SPC's mesoanalysis page. Radar presentation would suggest the cores of the strongest storms are producing small hail, though the general trend is toward weakening storms as instability continues to wane. CAMs suggest this activity will wane through daybreak, though the leftover outflow boundary may serve as a focus for a few lingering showers through afternoon by which time surface heating will bring a resurgence of instability. The High Resolution Ensemble Forecast (HREF) and Rapid Ensemble Forecast System (REFS) mean SBCAPE climb to 1000-1500 J/kg by late afternoon, though forecast soundings also advertise a capping inversion which should inhibit realization of that instability until LLJ ramps up during the evening.

With enough sunshine, deep mixing will promote temperatures warming into the upper 70s to low 80s by mid afternoon. It will also result in gusty southwest winds, with Bufkit soundings showing winds approaching 40 kt (46 mph) at the top of the mixed layer - a reasonable estimate for peak gusts - in east central Illinois. Given we had blowing dust yesterday afternoon with similar wind speeds, we elected to issue a Blowing Dust Advisory for areas north of I-70 and east of the Illinois River, where the risk appears greatest due to soil type and expected winds. (While several of the counties in this Advisory received rain from storms early this morning, the spotty nature of that rainfall and tendency for the near surface topsoil to quickly dry out made us think the potential is still significant enough, particulary along highways, to issue.)

***** STRONG STORMS TONIGHT, RAINY AND COOL TUESDAY *****

As a 40-50 kt LLJ ramps up ahead of a cold front this evening, scattered storms are forecast to develop, posing primarily a risk for locally damaging winds and large hail given steep mid level lapse rates and dry air in both the mid levels and below cloud bases (around 850mb). Given high LCLs, the tornado risk appears low (less than 2%), but SPC maintains a level 1 of 5 (marginal) risk for wind and hail. After midnight, coverage of storms is slated to increase while instability gradually wanes, lowering the risk for severe weather but bringing more widespread rain, which will continue in waves into tomorrow night. While this rainfall will be spread out over 24+ hours, we can't fully rule out hydrological issues south of I-72/Danville where some spots received up to 5 inches last week and where NBM gives a 5-15% chance for more than 2 inches; WPC has a level 1 of 4 (marginal) risk for excessive rainfall near and east of a roughly Shelbyville to Danville line. Behind the cold front tomorrow into Wednesday, it'll be quite chilly with afternoon highs in the mid to upper 50s.

***** STAYING COOL WITH LOW PRECIP CHANCES LATE WEEK *****

The parent upper level trough will linger over Ontario late week, with shortwaves orbiting it and offering the local area with periodic, low (15-30%) shower chances and shots of chilly Canadian air through the early part of the weekend. While global models and their respective ensembles differ in how long it will take for this upper level trough to retreat to the northeast, NBM's probabilistic distribution for daily high temperatures shifts up each day Thursday through Saturday. For example, the 25th percentile (75% chance of warmer temperatures) in Lincoln increases from 57 Thursday to 65 Friday to 70 Saturday.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 630 AM CDT Mon May 4 2026

All sites will start as VFR this morning with scattered to broken mid clouds around 8-10kft. The mid clouds will hang around for SPI, DEC, and CMI during the day while PIA and BMI will see scattered clouds continue. SPI, DEC, CMI may see some scattered showers late this morning through the after noon, but then have a break late afternoon. All sites will see convection develop around 00z and be on and off through the evening and then again around midnight. Will have PROB30 for all sites for thunder and reduced vis to 4sm. Cigs should remain VFR. Winds will be southwest most of the period, but then as the front moves through winds will shift to more westerly. Speeds will be light this morning but then increase with gusts reaching to around 30kts for this afternoon which could bring blowing dust to BMI, SPI, and CMI...sites that have some farm fields around. Speeds will decrease during the evening but still be around 12kts.

ILX WATCHES/WARNINGS/ADVISORIES

Blowing Dust Advisory until 6 PM CDT this evening for ILZ031- 037-038-041>048-050>057-061.