textproduct: Central Illinois

KEY MESSAGES

- Flooding continues across portions of central IL in a corridor from Fulton and southern Knox County to Vermilion County due to 4 to 7 inches of rain that fell yesterday and additional rain moving through this morning.

- Additional clusters of thunderstorms are forecast again late this afternoon into the overnight hours. SPC has a slight risk (level 2 of 5) south of I-70 and a marginal risk for areas east of the IL River Valley for damaging winds.

- Cooler and less active weather is on deck after today. Monday will have highs in the 80s and dry weather in place.

UPDATE

Issued at 1047 AM CDT Sun Aug 16 2026

Most of the precip has ended or decreased significantly; however, widely scattered showers and t-storms will continue across most of central IL as a boundary slowly shifts south across the area this afternoon into this evening and the remnants of an MCS/MCV move out of northeast MO into IL.

Watching this MCV over MO and several things to note for it decreasing. 1. Tops have trended warmer as it moves east. 2. Lightning has decreased. 3. Current HiRes guidance suggests a continuing weakening trend. However, there are trends for it continuing. 1. HiRes models have been doing a poor job over the last several days, so confidence in them is not as high as desired. 2. It is moving into a moist environment with SBCAPE over 3000, MLCAPE around 1000 and forecasted to be between 1000 and 1500 this afternoon. 3. Weakening CIN. 4. Mid level lapse rates near 6.5 C/km. and 5. Satellite showing some ACCAS at the mid levels in west central IL.

So, summing this all up. I think this convection will continue to move into central IL around noon and continue into this afternoon. So have increased pops/wx over this area to account for said convection, but did trend toward weakening as it move further east into central IL and as it continues east due to increasing cloud cover that should limit instability this afternoon. Have also made adjustment to pops/wx for this evening into tonight and increased pops as boundary to north will slowly drop across central IL. Models are all consistent with additional convection developing west and moving across central IL this evening from west to east, mainly along and south of I-72/Danville.

In addition, have already cancelled flood watch as not additional flooding is expected in that area. Heat Advisory does continue in southeast through early this evening.

DISCUSSION

Issued at 153 AM CDT Sun Aug 16 2026

Tonight more showers and storms will be moving across central IL. The main concern is the flash flooding risk. WPC has a small area of eastern IL in a moderate risk (level 3 of 4) and near and north of I- 72 in a slight risk (level 2 of 4) for excessive rainfall for the overnight hours (valid until 12z). The 00z sounding shows the environment having PWATs of 2.2-2.4 inches again. Flooding is already ongoing in many places, left over from last night's event. It will not take much to exacerbate the situation overnight if the new convection decides to set up over that stripe of central IL (Fulton Co to Vermilion Co) again. LPMM is suggesting that we could see another localized stripe of 4-8 inches somewhere in the area north of I-72.

There is a slight risk (level 2 of 5) south of I-70 and a marginal risk for areas east of the IL River Valley for damaging winds again today. The NAMNest is depicting a more widely dry, nearly no activity, solution. The HRRR has an area of convection developing late afternoon in west central IL, progressing eastward into the overnight hours with the cold front. After how much rain north of I- 70 has received over the last several days, the hope is for the drier solution, but plan for the stormier solution. With the HRRR version of events, it is showing pockets of 2-4 inches of rainfall from 21z-09z today into tomorrow. The good news though would be that if this activity were to develop, it would be fairly progressive and less of a training set up, unlike previous days.

Temperatures remain hot and humid for one more day. The heat advisory for south of I-70 is valid through 8pm (01z) this evening. Heat indices of 100-105 degrees are expected.

A brief break in the active weather and the heat is looking likely for Monday into Tuesday. A high pressure center will set up over the Upper Mississippi Valley / Great Lakes region behind a cold front that will move through central IL during the day today. Temperatures starting Monday into much of the next week will be mainly in the upper 70s to 80s for highs and 60s to low 70s for lows.

More showers and thunderstorm re-enter the forecast by Tuesday evening into Wednesday. SPC has central IL in a marginal risk for severe weather for Tuesday west of I-55, which would be for the late day convection. There are additional chance for rain through Thursday before returning to a mostly dry forecast into the late week.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 556 AM CDT Sun Aug 16 2026

VFR conditions are expected outside of any heavy shower or thunderstorm activity. If a heavier shower/storm moves through a site this morning, MVFR ceilings/visibilities are possible. Light northwesterly winds are expected the entire period becoming calm overnight tonight. Another round of storms are forecast for late this evening into the overnight hours, but time/location are uncertain so PROB30 was used between 02z to 08z.

ILX WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM CDT this evening for ILZ066>068- 071>073.