A slow-moving cold front interacting with a warm and very humid airmass resulted in scattered thunderstorms during the afternoon and evening of June 27th. One cluster of storms dropped heavy rainfall of 2 to 4 inches in Mattoon in Coles County, causing localized flash flooding and a few road closures.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS ILX wrote it up.
A slow-moving cold front interacting with a warm and very humid airmass resulted in scattered thunderstorms during the afternoon and evening of June 27th. One cluster of storms dropped heavy rainfall of 2 to 4 inches in Mattoon in Coles County, causing localized flash flooding and a few road closures.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Lincoln, IL wrote its last area forecast discussion before the first event at Jun 27, 7:16 PM CST, 2 hours 5 minutes earlier.
Area Forecast Discussion National Weather Service Lincoln IL 816 PM CDT Sun Jun 27 2021 .SYNOPSIS... Issued at 816 PM CDT Sun Jun 27 2021 Periods of showers and thunderstorms will continue across central and southeast Illinois through mid week. The warm and humid air mass will favor heavy rain in the stronger storms. Expect highs in the 80s the next few days, but closer to 90 degrees south of I-70. && .UPDATE... Issued at 816 PM CDT Sun Jun 27 2021 A weak boundary extends from near Jacksonville to Hoopeston this evening, with earlier outflows triggering the convection just north of I-70. Activity has been weakening as we get to sunset, after localized rainfall of 1 to 3 inches in the heavier storms earlier. Luckily this largely fell outside of the areas that were hammered over the last couple days, and there was enough of a northward drift to avoid excessive training echoes. Additional convection expected to form later as the boundaries lift northward, with the higher rain chances shifting into the northern CWA which has mostly stayed dry thus far. Updated zones/grids sent, mainly concentrating on the rain trends. && .SHORT TERM...(This evening through Monday night) ISSUED AT 316 PM CDT Sun Jun 27 2021 An omega block remains in place over the western CONUS with a large trough/southwest flow positioned over the Midwest states. A quasi- stationary cold front is stretched from a surface low located over MI southwestward across west-central IL and into the southern Plains states. To the west of the front westerly winds and slightly lower dewpoints are present, with southerly winds and dewpoints in the 70s to the east of it. SPC mesoanalysis as of 3 PM depicts MLCAPE of 1500+ J/kg across a good chunk of the CWA, though values quickly drop off closer to the aforementioned quasi-stationary cold front where a CAP is in place. The best shear is located across our northwest counties and points north/west of there, nearest to the upper trough. Scattered storms have developed across parts of southeast IL where the best instability is, though with limited shear these storms will struggle to stay organized. Further north, a remnant outflow boundary stretched from roughly Jacksonville to Rantoul will be the focus going into this evening where a few stronger storms could occur. This area also is co-located with a gradient of instability and bulk shear of 25-30 kts. Main threats look to be damaging winds and heavy rainfall. Weak 0-1 km shear will limit the tornado threat today, but with a boundary present will need to watch for any localized backing of winds within storms. The quasi-stationary front lifts north tonight as a subtropical high builds further westward. Shower and storm chances will follow suit and lift north into northwest counties of the CWA overnight into Monday. Dewpoints in the 70s and diurnal heating will allow instability to climb to near 1000+ J/kg by afternoon, though limited shear will keep the severe weather threat low. Heavy rainfall is of concern though with current thinking plotting anywhere from 1-2" along and northwest of the IL River through Monday night. Although this area can take some rain, will need to keep rainfall rates in mind with forecast models indicating PWATs upwards of 2" and warm cloud depths of 4 km. && .LONG TERM...(Tuesday through Sunday) ISSUED AT 316 PM CDT Sun Jun 27 2021 Little movement in the upper pattern keeps southwest flow positioned aloft and a warm and humid airmass in place at the surface. A shortwave trough in the large upper trough will swing through the Great Lakes Region later on Tuesday into Wednesday, reinforcing shower and storm chances along the stationary boundary draped across the Midwest southwestward through the southern Plains. This shortwave will also work to deamplify the subtropical high going into midweek and finally allow the pattern aloft to break the block and bring a change in airmass by the end of the week. The stationary front looks to drop south of the local area later Thursday into Friday, putting an end to daily shower/storm chances. High pressure builds in it's wake with what looks to be a great Fourth of July weekend with drier, less humid, and near to slightly below normal temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 626 PM CDT Sun Jun 27 2021 Main aviation concerns recently have been with convection at KDEC/KCMI, though this has been weakening recently along the northern edge. Scattered showers/storms are expected to spread northward with time this evening, potentially reaching KBMI toward 04-05Z. While some thunder may linger past 06Z, currently there is not enough confidence to keep the mention going that long. Most places are expected to remain VFR outside of any storms. The exception will be at KPIA, which will be on the edge of a lower cloud deck after 06Z. Will continue with a mention of MVFR ceilings overnight into Monday morning there. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && UPDATE...Geelhart SYNOPSIS...Geelhart SHORT TERM...NMB LONG TERM...NMB AVIATION...Geelhart
Hazardous Weather Outlook National Weather Service Lincoln IL 321 PM CDT Sun Jun 27 2021 ILZ027>031-036-037-040-041-281100- Fulton-Knox-Marshall-Mason-Peoria-Schuyler-Stark-Tazewell- Woodford- 321 PM CDT Sun Jun 27 2021 This Hazardous Weather Outlook is for portions of central Illinois and west central Illinois. .DAY ONE...TONIGHT... Scattered thunderstorms are possible later this evening and overnight. These storms are not expected to be severe, but some of the storms may have heavy rain. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY... Thunderstorms are possible Monday through Thursday. The potential for widespread severe weather is low. However, locally heavy rain will be possible. Minor flooding is expected to develop along the Illinois River through Tuesday, then linger into the weekend. Minor flooding is likely near Havana by Thursday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated through tonight. ILZ038-042>057-061-281100- Cass-Champaign-Christian-Coles-De Witt-Douglas-Edgar-Logan-Macon- McLean-Menard-Morgan-Moultrie-Piatt-Sangamon-Scott-Shelby- Vermilion- 321 PM CDT Sun Jun 27 2021 This Hazardous Weather Outlook is for portions of central Illinois and east central Illinois. .DAY ONE...TONIGHT... Scattered thunderstorms are expected through tonight. While there is not a widespread severe weather risk, a few of the storms may produce brief damaging wind gusts this evening. Locally heavy rain will also be a possibility. Minor flooding will continue along portions of the Sangamon River upstream from Decatur. Other smaller rivers and creeks will also see flooding in response to the recent heavy rain. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY... Thunderstorms are possible Monday through Thursday. The potential for widespread severe weather is low. However, locally heavy rain will be possible. Minor flooding will expand along much of the Sangamon River through the week. .SPOTTER INFORMATION STATEMENT... Spotter activation may be required through this evening. ILZ062-063-066>068-071>073-281100- Clark-Clay-Crawford-Cumberland-Effingham-Jasper-Lawrence-Richland- 321 PM CDT Sun Jun 27 2021 This Hazardous Weather Outlook is for portions of southeast Illinois. .DAY ONE...TONIGHT... Scattered thunderstorms are expected through tonight. While there is not a widespread severe weather risk, some of the storms will produce locally heavy rain. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY... Thunderstorms are possible Monday through Friday. The potential for severe weather is unknown at this time. However, locally heavy rain will be possible. Minor flooding is possible along portions of the Wabash River around mid week. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated through tonight. Geelhart
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LINCOLN IL
1008 PM CDT SUN JUN 27 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1000 PM HEAVY RAIN COLES COUNTY AIRPORT 39.48N 88.28W
06/27/2021 M2.89 INCH COLES IL ASOS
1.21 INCHES BETWEEN 4-7 PM, AND ANOTHER 1.68
INCHES FROM 7-10 PM.
&&
GEELHARTThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Portions of IL-16 east of downtown Mattoon were closed due to flooding. IL-316 and US-45 on the north side of town were also closed. Some vehicles were stranded in high water.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2021Every state in 2021This day in weather historyWarnings in Illinois, June 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 962352.