Temperatures in the 90s and high moisture in the low levels led to diurnally driven thunderstorms on Friday, June 11th. Weak upper level support kept these storms relatively isolated and short-lived.
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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 DVN wrote it up.
Temperatures in the 90s and high moisture in the low levels led to diurnally driven thunderstorms on Friday, June 11th. Weak upper level support kept these storms relatively isolated and short-lived. Another focus area for convection was along a remnant outflow boundary from an MCS that morning, which led to some further storm development later in the day. One storm reached severe limits, which was seen in Burlington, Iowa. This storm resulted in strong downburst winds over 70 mph, that lead to multiple damaged trees and some buildings damaged.
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 Quad Cities, IA wrote its last area forecast discussion before the first event at Jun 11, 12:25 PM CST, 1 hour 7 minutes earlier.
Area Forecast Discussion National Weather Service Quad Cities IA IL 125 PM CDT Fri Jun 11 2021 .SYNOPSIS... Issued at 117 PM CDT Fri Jun 11 2021 A hot a humid airmass has acted similar to past days in developing small scale deep convection shortly after reaching convective temperature, in this case, a bit warmer than previous days, at 89. This is occurring in all areas, in isolated nature, while upstream and now entering our northwest, an outflow boundary from overnight storms is enhancing coverage of storms in our northwest and western CWA. While these are not acting on an aggressive cold pool, it's helping organize some of the activity into a line. This feature is not handled by any current model but non the less is occurring. && .SHORT TERM...(This Evening through Saturday) ISSUED AT 117 PM CDT Fri Jun 11 2021 The outflow and isolated storms will rule the afternoon, and bring at least temporary relief from heat index readings which are in the 95 to 100 range this afternoon. We'll need to watch for strong cells, which would be capable of producing 40 mph winds, especially in the northwest, and northeastern CWA, where stronger winds aloft are in place. Tonight, the cold front, or at least dry air front, will arrive. There is a signal that some new convection may form alone the front in the Midnight to 6 AM time frame. Like today's storms, the atmosphere will be capable of heavy rains and gusty winds, but not really favorable for severe storms. These are most likely in the north half of the area and by Saturday morning, will be exiting the region to the east. Saturday will be warm, breezy, and gradually seeing dry air spread in. Thus, the late afternoon will be the best part of the day for outdoor activity, with dewpoints crashing as low as the upper 40s in Iowa, and 60s in Illinois. This the beginning of a drier air high pressure looking to be in place much of the week. .Previous LONG TERM...(Saturday through Thursday) ISSUED AT 330 AM CDT Fri Jun 11 2021 New long term section will still be sent this afternoon. Saturday and Sunday...Post-frontal LLVL flow to continue to veer and deepen on Saturday, but lingering boundary layer moisture and based CAPE levels build enough for the chance of isolated buoyancy pop up type showers or even a thunderstorm in the southeast third to half of the DVN CWA from late morning and to late afternoon, before ridge bulge aloft/increasing height fields shunt activity off to the east and south by Sat evening. But most areas to be dry during the day, and increasing north breeze to scour out the higher DPTs from north- to-south with noticeable decrease during the afternoon and evening period...upper 60s in the morning decreasing well down in the 50s by late afternoon. Ambient high temps still to be more toward the hot site withe another deep mix day making for widespread upper 80s to low 90s. Sat night cool down with incoming sfc ridge lobe, temps into the low to mid 60s in many areas, with a chance for some upper 50s north of Hwy 30. On Sunday, a deep mix into a dried out airmass under the strongest sun angle of the year will still lead to very warm temps even post-frontally, with highs back into the upper 80s to around 90. But sfc DPTs mixed down into the 50s or even upper 40s, afternoon humidity levels to be low in the 30s or even 20s. Sunday night lows in the 60s. Monday through next Thursday...Monday a similar day to Sunday, before continued steering flow amplification to near meridional extent from the western Hudson Bay region down the western GRT LKS and to the western OH RVR Valley brings about back-door style cooling high pressure re-enforcement Tue into Wed. Monday night lows may be more widespread upper 50s to low 60s, Tue highs in the low to mid 80s, and then the Wed thermo-signal cools down low level temp pool enough for more widespread lower 80s. Northeasterly LLVL flow fetch may keep some areas closer to LK MI in the 70s on Wed. Anyway, some ideal WX temp-wise or the mid week period. Flattening mid CONUS flow pattern and sfc high migration to the southeast of the region to allow return flow warming on Thu and boosting temps back above normal. Some longer range signals suggesting a northern stream wave to help shunt a boundary down through the region from the upper MS RVR Valley either Thu night or Sunday and that may be the next best chance for a more organized precip chance at the end of the period. && .AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon) ISSUED AT 1218 PM CDT Fri Jun 11 2021 A large, decaying area of showers and thunderstorms over central Iowa will push east, largely only resulting in a wind switch to west winds over eastern Iowa and Illinois, and a few isolated thunderstorms. Isolated storms will be possible through late tonight, until a cold front arrives, with dry air behind it towards 12Z. A somewhat better chance for thunderstorms will exist overnight when the front gets here, and that's handled with a prob30 period during the overnight hours in sites along and north of Interstate 80. ERVIN && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && SYNOPSIS...Ervin SHORT TERM...ERVIN LONG TERM...12 AVIATION...Ervin
Hazardous Weather Outlook National Weather Service Quad Cities IA IL 403 AM CDT Fri Jun 11 2021 IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007- 009-015>018-024>026-034-035-MOZ009-010-120915- Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson- Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson- Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll- Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson- Warren-Hancock-McDonough-Scotland-Clark- 403 AM CDT Fri Jun 11 2021 This Hazardous Weather Outlook is for portions of north central Illinois...northwest Illinois...west central Illinois...east central Iowa...northeast Iowa...southeast Iowa and northeast Missouri. .DAY ONE...TODAY AND TONIGHT There is a chance of thunderstorms this afternoon and tonight. The main threats from any storms will be lightning, gusty winds, and torrential downpours. It will remain hot and humid today with afternoon heat indices topping out in the mid 90s to near 100 degrees. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not anticipated today or tonight.
Special Weather Statement National Weather Service Quad Cities IA IL 1038 AM CDT Fri Jun 11 2021 IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007- 009-015>018-024>026-034-035-MOZ009-010-112000- Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson- Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson- Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll- Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson- Warren-Hancock-McDonough-Scotland-Clark- Including the cities of Independence, Manchester, Dubuque, Vinton, Cedar Rapids, Anamosa, Maquoketa, Marengo, Iowa City, Tipton, Clinton, Muscatine, Davenport, Bettendorf, Sigourney, Washington, Wapello, Fairfield, Mount Pleasant, Burlington, Keosauqua, Fort Madison, Galena, Freeport, Mount Carroll, Sterling, Moline, Rock Island, Geneseo, Princeton, Hennepin, Aledo, Oquawka, Monmouth, Carthage, Macomb, Memphis, and Kahoka 1038 AM CDT Fri Jun 11 2021 ...Heat Index of 95 to 100 this Afternoon... Hot temperatures in the lower 90s will combine with dewpoints near 70 today to bring heat index readings of 95 to 100 through this afternoon. If you plan to be outside, avoid prolonged exposure to the heat or strenuous activity. Drink plenty of fluids to avoid dehydration.
Special Weather Statement National Weather Service Quad Cities IA/IL 218 PM CDT Fri Jun 11 2021 ILC067-071-IAC057-111-111945- Hancock-Henderson-Des Moines-Lee- 218 PM CDT Fri Jun 11 2021 ...A STRONG THUNDERSTORM WILL AFFECT NORTHERN HANCOCK...SOUTHERN HENDERSON...SOUTHERN DES MOINES AND NORTHEASTERN LEE COUNTIES UNTIL 245 PM CDT... At 217 PM CDT, a strong thunderstorm was located over West Burlington, or near Burlington, moving southeast at 10 mph. Winds in excess of 40 mph and penny size hail are possible with this storm. Locations impacted include... Burlington, West Burlington, Dallas City, Danville, Stronghurst, Middletown, Carman, Gulf Port, Iowa Army Ammunition Plant, Lomax, Shokokon, Spring Grove, Beaverdale, Decorra, Lone Tree, Carthage Lake, Heapsville, Starr's Cave Park and Preserve, Burlington Regional Airport and Prairie Grove. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. LAT...LON 4086 9132 4097 9112 4075 9085 4060 9114 TIME...MOT...LOC 1917Z 324DEG 10KT 4086 9117 Ervin
Special Weather Statement National Weather Service Quad Cities IA/IL 226 PM CDT Fri Jun 11 2021 ILC161-IAC163-112000- Rock Island-Scott- 226 PM CDT Fri Jun 11 2021 ...A STRONG THUNDERSTORM WILL AFFECT SOUTH CENTRAL ROCK ISLAND AND SOUTH CENTRAL SCOTT COUNTIES UNTIL 300 PM CDT... At 226 PM CDT, a strong thunderstorm was located over Rock Island, moving southeast at 15 mph. Winds in excess of 40 mph and penny size hail are possible with this storm. Locations impacted include... Davenport, Moline, Rock Island, Bettendorf, East Moline, Silvis, Milan, Riverdale, Carbon Cliff, Blackhawk State Park, Silvis Heights, West Lake Park, Fruitland, Rock Island Arsenal, Indian Bluff Golf Course, Mississippi Valley Fairgrounds, Moline Quad-City Airport, Credit Island and Rock Island County Fairgrounds. This includes the following highways... Interstate 74 in Iowa near mile marker 5. Interstate 74 in Illinois between mile markers 1 and 5. Interstate 280 between mile markers 5 and 18. Torrential rainfall is also occurring with this storm. Minor flooding of low lying areas, creeks, streams and urban areas is possible. If you encounter water over a roadway, do not drive through it. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. LAT...LON 4152 9071 4155 9066 4151 9039 4141 9054 TIME...MOT...LOC 1926Z 302DEG 11KT 4150 9059 Ervin
The Quad Cities radar (KDVN), 101 km away, was scanning. The volume nearest the first event began at 19:30 UTC.
7 thunderstorm wind. Local standard time, as filed.
The roof of a church was damaged.
A wooden fence was partially damaged at Menards in West Burlington.
A large garage door was blown in at a factory.
A partial cinderblock wall collapsed at a small business on East Agency Road.
A large tree limb was blown down at Notre Dame High School.
A tree was partly down in Crapo Park.
A large tree limb was blown down onto a house.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2021Every state in 2021This day in weather historyWarnings in Iowa, 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: 957180, 957181, 957182, 957183, 957184, 957185, 957186.