textproduct: Central Illinois

KEY MESSAGES

- Periodic strong to severe storm chances will persist through early next week...with the greatest probability for convection focusing on Saturday...then again late Monday into Tuesday.

- After a couple more mild days, a preview of summer will arrive by early next week as highs soar into the 80s by Saturday into Tuesday.

DISCUSSION

Issued at 238 AM CDT Fri May 15 2026

An active period of weather is in place through the weekend into early next week. Tonight, a shortwave will pass overhead, bringing a MCS into IL. As of now (2AM), storms have begun to multiply and grow along and west of the Mississippi River then will continue to move east through IL. The system as a whole will be moving into a less supportive environment, so it is expected to be elevated and sub severe. Rainfall amounts are forecast to be generally less than half an inch through 18z.

This evening into tonight may have additional showers and thunderstorms, of which could be strong to severe. Most of the day after noon should be pretty dry for much of central and southeastern IL. Hefty capping (500-800 CIN) will be in place during this time, which may stunt the development of any storms. Bulk shear of 30-40 knots. MUCAPE values of 1000-2000 J/kg. SPC has a marginal risk (level 1 of 5) for damaging winds and large hail during this time for west of I-57. The CAMs show the system moving in from Iowa to be decaying as it approaches the forecast area around midnight.

Saturday, another marginal risk for severe weather is in place for all of central IL and most of southeastern IL. Sufficient deep- layer shear and 1000-2000 J/kg of MUCAPE as another weak shortwave passes overhead should support an isolated severe threat with damaging wind gusts. The storms may struggle to develop since the lift source won't be very strong. However, any that do develop have a very supportive environment to become severe.

Beyond Saturday, there looks to be the potential for more waves of severe weather into the new week, including Knox, Fulton, and Stark counties having a marginal risk Sunday. There is a 15% chance (equal to a slight risk) for severe weather from SPC for Monday along and west of I-55 and Tuesday for most of the forecast area. We will continue to monitor but will need to make it through the next 3 days of severe weather before pinning anything down for Sunday-Tuesday.

Today is the coolest day for a few days with highs only in the mid to upper 70s. Otherwise, temperatures are going to be warm through early next week with highs in the 80s and lows in the 60s, near 70.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1245 PM CDT Fri May 15 2026

Skies have cleared everywhere west of the I-57 corridor and will clear at KCMI by 19z. The remainder of the afternoon and evening is expected to be dry before scattered convection develops late tonight into Saturday morning. Exact timing of the convection remains in question: however, the HRRR/RRFS consensus suggests showers arriving at KPIA by around 08z, along I-55 by 09z, then further east to KCMI by 10z. The precip will gradually come to an end from west to east by mid to late Saturday morning. Thunder chances appear highest at the western terminals with much lower probabilities further east. Based on the latest data, have opted to include a PROB30 for thunder at all sites except KCMI between about 08z and 13z. Winds will initially be S/SE with gusts of 20-25kt this afternoon, then the gusts will drop into the 15-20kt range toward sunset. Some CAMs suggest an outflow boundary will cause winds to temporarily veer to NW after the 08z/09z time frame, but have omitted that detail from the TAFs until better model/observational information becomes available.

ILX WATCHES/WARNINGS/ADVISORIES

None.