Basic Summary: A cluster of storms in northeast Nebraska and southeast South Dakota developed into the destructive derecho that raced eastward across large portions of Iowa, northern Illinois, southern Wisconsin, northern Indiana, and southern Michigan during the morning and afternoon of August 10th. The strongest winds were experienced in central and east-central Iowa where 100+ mph winds were…
Every event with a place to put it. Tap one for its entry below.
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 DMX wrote it up.
Basic Summary: A cluster of storms in northeast Nebraska and southeast South Dakota developed into the destructive derecho that raced eastward across large portions of Iowa, northern Illinois, southern Wisconsin, northern Indiana, and southern Michigan during the morning and afternoon of August 10th. The strongest winds were experienced in central and east-central Iowa where 100+ mph winds were observed. Some of the strongest winds were in an area from roughly Marshalltown, IA eastward along the Highway 30 corridor to the Mississippi River, where estimated winds exceeded 120+ mph and approached 140 mph. A number of QLCS tornadoes were also experienced within the Highway 30 corridor. One of the most remarkable aspects of the derecho was the duration of severe winds, with many areas experiencing at least periodic, if not persistent, severe level (58+ mph) winds over a roughly 30 minute time frame. As the derecho moved eastward out of Iowa, it continued to expand, but weakened from its peak strength. Winds continued to exceed severe criteria (58+ mph) in Illinois, Wisconsin, Indiana, and Michigan and began to produce additional QLCS tornadoes across northern Illinois before fading out across northern Indiana and southern Michigan.
In the wake of the derecho, damage was substantial in many areas, rural and urban. Many agriculture fields, mainly corn, were flattened within the swaths of strongest winds. Initial estimates suggest at least 850,000 acres of partial or complete crop loss occurred from this event. Within urban and wooded areas extensive tree and structure damage was seen, including complete roof failure in a few instances. At its peak, total estimated customers without power exceeded 1.4 million across the affected states. In total, early estimates on losses (agriculture, infrastructure, private property) have exceeded $7.5 billion across the states affected.
Environment: Broadly speaking, it was a ripe day for thunderstorms across the affected area with MUCAPE values often exceeding 3500-4000 J/kg by the mid morning hours concurrent with mid-upper level short wave support, and indications that any cold pool development would be strong (difference between cold pool and ambient air) and potentially long lived. For detailed environmental analysis, including soundings, please view the various local NWS office event review pages: NWS Des Moines, NWS Quad Cities, NWS Chicago, NWS Milwaukee, NWS Central Illinois, NWS Northern Indiana, or NWS Indianapolis.
Additional Details: Numerous injuries occurred during the derecho and in the aftermath during cleanup, including 4 direct and indirect deaths of which 3 occurred in Iowa (two in Poweshiek County and one in Linn County) and 1 in Indiana (Fort Wayne).
Disclaimer: The August 10, 2020 derecho resulted in widespread high-end damage across large portions of central and southern Iowa. Given the size and scope of the event and understanding that final damage and loss estimates (agriculture, infrastructure, and private property) will take months to complete, the NWS is not able to estimate the monetary impact at this time. Values may be added as more data becomes from various sources in future months.
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 Des Moines, IA wrote its last area forecast discussion before the first event at Aug 10, 8:30 AM CST, 0 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 930 AM CDT Mon Aug 10 2020 .UPDATE... Issued at 929 AM CDT Mon Aug 10 2020 Line of severe convection moving into west-central Iowa continues to intensify this morning. Plenty of instability out of ahead of this line and judging by the previous wind reports, there is a well established cold pool. Downdraft CAPE ranges from 1000-1500 J/kg with effective shear 30-40 knots in the vicinity of the convection. Further east however, the 0-6km shear is currently not conducive for sustainable strong storms as it is barely 25 knots as far east as Interstate 35. The outflow from this storm has been producing severe wind gusts in the southwest part of the state and appears the outflow remains connected with the main convection in Crawford County. Expecting the Des Moines Metro to get impacted by this line b/t 11 AM to 12 PM and potentially with severe winds. && .DISCUSSION.../Today through Sunday/ Issued at 245 AM CDT Mon Aug 10 2020 We are anticipating another active morning across portions of the forecast area as an approaching shortwave trough and associated surface front trigger convective development. As of 07z radar returns were quite isolated with small convective complexes noted in northeast Nebraska and near the Twin Cities. Hi-res models initiate more thunderstorm activity in the next few hours as deeper kinematic ascent overspreads the area. Favored corridor this morning continues to be northern Iowa, although convective evolution remains in question especially given the poor performance of the hi-res model suite last night. Sluggish progression of the upper wave keeps some degree of kinematic and thermal support for ascent over the area through much of the day, so expecting additional showers and storms along and behind a southerly sagging cold front. Hi-res models vary from isolated to widespread precip, so potential rainfall coverage and amounts are tough to pinpoint. Ample surface instability builds for a few strong to severe storms along the front later this afternoon and evening, mainly south of I-80. The corridor of stronger winds aloft lags behind the frontal boundary and limits deep layer shear, but should still be strong enough to support some organized updrafts capable of large hail and strong winds. It is worth noting that a faster frontal progression would push the threat south of the state border, but that hinges on the extent morning convection augments the cold front. Precip chances slowly wane across southern Iowa Monday night, giving way to a mainly dry Tuesday as a surface high pressure tracks through the state. Forecast is somewhat muddled over mid to late week. Zonal flow aloft eventually becomes southwesterly as a large trough drops into the northern Rockies. Models show multiple weak shortwaves within the mean flow crossing the region, but provide little agreement on timing/location. Favored areas of ascent and surface convergence are also rather nebulous, which makes it difficult to improve on the broad brushed low chance PoPs in the latest NBM output. Ensemble data continues to cluster highest precip chances around Thursday, but confidence in any sort of widespread precip event is low at this time. High temperatures remain seasonal in the 80s through most of the forecast period. && .AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/ Issued at 617 AM CDT Mon Aug 10 2020 MVFR cigs and tsra associated with a cold front passage are the main forecast challenge through the current TAF period. MVFR cigs currently stretch from KFOD to KMCW, ahead of tsra activity moving out of SD. This is expected to impact terminals in north central Iowa by mid to late morning. Confidence decreases further south toward KDSM, but model guidance suggests tsra holds off until late morning or afternoon. VFR conditions expected to prevail across the area by late this evening into the overnight hours. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && UPDATE...Podrazik DISCUSSION...Martin AVIATION...Martin
Hazardous Weather Outlook National Weather Service Des Moines IA 902 AM CDT Mon Aug 10 2020 IAZ023>028-033>039-044>050-057>062-070>075-084>086-111415- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene- Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper- Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Lucas-Monroe- Wapello- 902 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Severe thunderstorms are expected this morning and afternoon. The storms are likely to be severe with damaging winds. A few storms may also produce tornadoes along with some hail and brief heavy rainfall. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Periodic thunderstorms chances continue though the second half of the week, however at this time the severe threat is uncertain. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed today. IAZ004>007-015>017-111415- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- 902 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms are forecast today as a cool front moves across the state. A few storms could be severe with damaging winds and some hail the main threats. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Periodic thunderstorms chances continue though the second half of the week, however at this time the severe threat is uncertain. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed today. IAZ081>083-092>097-111415- Adams-Union-Clarke-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 902 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms are forecast today as a cool front moves across the state. A few storms could be severe with damaging winds and some hail the main threats. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Periodic thunderstorms chances continue though the second half of the week, however at this time the severe threat is uncertain. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed today. REV
The Omaha radar (KOAX), 129 km away, was scanning. The volume nearest the first event began at 14:32 UTC.
105 thunderstorm wind, 4 tornado, 1 hail. Local standard time, as filed.
Law enforcement reported a semi jackknifed due to strong winds.
Law enforcement reports tree damage in town and throughout the county. A tree also fell on neighbors car. Time estimated.
A trained spotter reported a large tree limb 6 inches in diameter and 20 feet long was downed. Several smaller limbs were downed as well.
Law enforcement reported tree damage occurred all across town.
Law enforcement reported tree damage occurred all across town.
No LSRs were transmitted from within the county during the August 10 derecho event. However, it is estimated by the NWS that areas of the county experienced severe winds and associated damage based on surrounding county LSRs and other available information.
No LSRs were transmitted from within the county during the August 10 derecho event. However, it is estimated by the NWS that areas of the county experienced severe winds and associated damage based on surrounding county LSRs and other available information.
Wind-driven hail caused significant damage northeast of Breda. Winds Estimated to be 60 mph or greater. Delayed Report. Time estimated by radar.
Emergency manager reported an outbuilding had the roof blown off. Time estimated via radar.
A trained spotter reported 8 inch tree limbs down, power lines down, and trees down all over town.
AWOS reported a gust of 64 knots.
Public report of 60 mph wind gust.
Mesonet reported a 56 knot wind gust.
A trainer spotter reported large trees down blocking roads. Wind was still blowing at time of report.
Trained spotter reported trees down. Wind was still blowing at time of report.
No LSRs were transmitted from within the county during the August 10 derecho event. However, it is estimated by the NWS that areas of the county experienced severe winds and associated damage based on surrounding county LSRs and other available information.
A personal weather station reported a 72 knot wind gust. Time estimated via radar.
A personal weather station reported a 72 knot wind gust. Time estimated via radar.
Emergency manager reported 65 mph wind gusts with pea sized hail and heavy rainfall.
Emergency manager reported 65 mph wind gusts with pea sized hail and heavy rainfall.
Emergency manager reported a two foot diameter tree limb down in Perry.
Public report of 70 mph winds with branches down and power out.
A trained spotter reported 70 mph wind gusts with debris on roads.
Trained spotter reported a large tree limb hit a home, causing the home to lose power.
Trained spotter reported a large tree limb hit a home, causing the home to lose power.
Fire department estimated 60 to 70 mph wind gusts.
Public estimate of winds over 60 mph with power flickering.
Public estimate of winds over 60 mph with power flickering.
A trained spotter reported winds over 60 mph with tree damage. Time estimated.
A trained spotter reported 70 mph winds with lots of small trees down and several anchored swing sets toppled over.
No LSRs were transmitted from within the county during the August 10 derecho event. However, it is estimated by the NWS that northern areas of the county experienced severe winds and associated damage based on surrounding county LSRs and other available information.
A trained spotter reported 70 mph gusts at Mills Civic Parkway and Interstate 35.
A trained spotter reported 70 mph gusts in the City of Adel with limbs down and objects blown around.
A public report of a semi blown over at US highway 30 and Highway 17 interchange. Time estimated via radar.
A trained spotter reported several large tree limbs down and power out.
A trained spotter reported damage to home foundation and several large trees down, plus a very large tree trunk down.
AWOS reported a 52 knot wind gust.
Trained spotter reported trees down and roof off building.
A trained spotter reported a 75 mph wind gust.
A trained spotter reported a 75 mph wind gust.
Public report of trees down and power out.
Public report of tree damage at 75th and Diamond in Urbandale.
Trained spotter reported numerous trees and power lines down. Time estimated.
A trained spotter reported 80 mph wind gusts with several large tree limbs down and tree trunks snapped. Roads were blocked.
Mesonet station reported a 60 knot wind gust.
Emergency manager reported numerous trees down along with power outages.
Trained spotter reported several large trees down throughout the town of Cumming. Time estimated by radar.
Public report of 60 mph wind gust.
Des Moines Airport ASOS reported a wind gust of 65 knots.
Public report via social media of roof damage to Buccaneer Arena at 72nd and Hickman Rd. Time estimated.
Trained spotter reported twelve to eight inch diameter trees down.
Mesonet station reported a 51 knot wind gust.
NWS employee reported 70 mph wind gusts and lots of small branches down.
A trained spotter reported 70 mph wind gusts.
A trained spotter reported branches down.
An NWS employee reported and uprooted tree in northwest Johnston. Time estimated.
A trained spotter reported six inch and larger tree limbs down with power outages. Severe winds lasted 30 minutes.
Mesonet station reported a 74 kts wind gust.
Mesonet station reported a 54 knot wind gust.
A trained spotter reported estimated wind gusts over 70 mph.
WOI TV relayed a report of trees down and damage to roofs.
WHO TV relayed a report that part of the Buccaneers Arena roof was blown off.
A trained spotter reported large tree branches down.
A trained spotter reported damage to trees and grain bins. Time estimated.
AWOS measurd a 68 knot wind gust.
Public report of a fence blown down at 128th and Douglas.
Public report via social media of lots of tree damage in Carlisle.
Trained spotter reported a large tree down.
Public report of trees down with power flickering.
Public report of winds gusts between 70 to 80 mph.
A trained spotter reported a large tree blocking both lanes of Highway F48 in Colfax.
A trained spotter reported wind gust on Iowa State University campus of 65 to 75 mph with extensive tree damage and power outages.
Public report of mailboxes, trees, and limbs of undetermined size down.
ASOS at Lamoni airport reported a 54 knot wind gust.
A trained spotter reported damage throughout town with trees down and roads blocked. Time estimated.
Brief QLCS tornado on leading edge of convection through agricultural fields. Path found via high resolution satellite imagery. The tornado impacted no damage indicators, hence the EFU rating.
A public report of 100 to 120 cars with windows blown out at a factory. Time estimated.
Public report of a 77 mph peak wind gust from a Davis home weather station. Tree branches two to three inches in diameter broke and a 4 inch tree broke off at the ground.
A trained spotter reported large tree branches down, street signs blown down in town, and part of a roof blown off a home. Time estimated.
Knoxville airport AWOS reported a 62 knot wind gust.
Brief tornado captured from post event UAS survey. Stayed in cropland with no impacts to damage indicators, hence the EFU rating.
Mesonet station reported a 67 knot wind gust.
Tornado initially found from high resolution satellite imagery and confirmed via UAS overflight. Damage was done to crop and trees. Some minor damage to housing structures as well, but mostly superficial.
Amateur radio report of multiple tree limbs down with the largest eight inches in diameter. Time estimated.
Mesonet station reported a 74 knot wind gust.
Emergency manager reported numerous large trees down with winds estimated at 70 mph.
The Marshalltown mesonet station reported a wind gust of 79 knots.
A trained spotter reported damage to barns and roofs.
Emergency manager reported roof damage to a home. Time estimated.
The ASOS at Marshalltown airport reported a gust of 86 knots with high winds still in progress.
A storm chaser reported several large sections of roofs blown off buildings along old highway 30 on south side of Marshalltown.
A storm chaser estimated winds between 90 to 100 mph.
Public report via social media of numerous trees and power lines downed.
A personal weather station reported a 92 knot wind gust.
Emergency manager reported wind gusts over 70 mph and that a tree fell on the office.
A mesonet station reported a wind gust of 65 knots.
Emergency manager reported significant damage in State Center with numerous cars blown off US 30 and flipped.
A trained spotter reported 75 mph wind gusts.
Public report of significant structural and tree damage. Time estimated.
A trained spotter reported 90 mph wind gusts.
Law enforcement reported a large tree fell on a home.
Tornado associated with QLCS derecho first observed via high resolution satellite imagery. Path was also overflown by UAS confirming convegent path of debris. No damage indicators were impacted, hence the EFU designation.
A coop observer reported a 60 by 90 foot machine shed completely demolished. Neighbors empty grain bins were blown across highway 63. Several large trees are snapped or uprooted. A 78 mph wind gust was reported before the weather station gave out.
A trained spotter reported a semi blown over on Interstate 80 just west of the Grinnell interchange.
Law enforcement reported damage to power lines in the area.
A trained spotter reported trees down across roads all over town. Time estimated.
A trained spotter reported 60 mph wind gusts with pea sized hail.
Public report of grain bins blown in and severely damaged. Widespread crop damage across Tama county. Time estimated.
Public report of grain bins blown in and severely damaged. Widespread crop damage across Tama county. Time estimated.
A trained spotter reported 60 mph wind gusts.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Thunderstorm Wind, Poweshiek | 2020-08-11 | 41 | Female | Permanent Home | Direct |
| Thunderstorm Wind, Poweshiek | 2020-08-10 | 41 | Male | Outside/Open Areas | Indirect |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2020Every state in 2020This day in weather historyThe tornado archive for Iowa, 2020Warnings in Iowa, August 2020
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: 918933, 919231, 918935, 918937, 918938, 919277, 919283, 918926, 918940, 918950, 919248, 919249, 919250, 918942, 918951, 919280, 919251, 919252, 919253, 919254, 918945, 919255, 919256, 918947, 918948, 919257, 919258, 919259, 919260, 919261, 919286, 919262, 919263, 918952, 918954, 918955, 919264, 918956, 919265, 919266, and more.