Strong thunderstorms initiated well to the west of the area the previous night, primarily in western South Dakota, and proceeded to track east southeast through the morning towards northern Iowa. By the afternoon, instability had picked up to around 3000-4000 J/kg MUCAPE with 50+ kts of effective bulk shear.
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.
Strong thunderstorms initiated well to the west of the area the previous night, primarily in western South Dakota, and proceeded to track east southeast through the morning towards northern Iowa. By the afternoon, instability had picked up to around 3000-4000 J/kg MUCAPE with 50+ kts of effective bulk shear. The result was a strong and damaging wind producing MCS that moved across north-central and northeast Iowa which produced a number of wind damage and wind gust reports.
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 Jul 19, 2:52 PM CST, 3 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 352 PM CDT Wed Jul 19 2017 .SHORT TERM.../Tonight through Thursday/ Issued at 352 PM CDT Wed Jul 19 2017 Thunderstorms over South Dakota early today moved southeastward into southern Minnesota this afternoon and attained an eastward trajectory while producing severe wind gusts. These storms have started to take a little more east-southeast turn recently as it follows the warm front from near the southwest Minnesota/northwest Iowa border and stretches back to north of Waterloo. Have also noted some failed attempts at convective initiation with orphan anvils per GOES-16 imagery in the last hour or so between Carroll and Des Moines. This is likely due to very warm 700mb temperatures around 14C. Otherwise, as the current storms over southern Minnesota move east-southeast, question remains on redevelopment later today and tonight. Best opportunity appears to be along boundary, with thunderstorm development near the South Dakota/Nebraska border. Expect additional storms to be able to form near the boundary this evening, but will be limited by warm temperatures aloft. However, development may become a bit more numerous as LLJ intensifies to 35 to 40 knots. Storms will be mostly east of the area by Thursday morning and the boundary will shift southward to south of the Highway 20 corridor. This will help to continue to focus the heat over the southern half or so of central Iowa tomorrow. Challenge continues to be dewpoints. With the dry conditions that have been occurring with D0 and D1 drought over parts of the southwestern half of the state, don't have as much moisture available to evapotranspirate. Have seen observations this Wednesday afternoon of dewpoints mixing out into the middle 60s. This has kept heat indices less than anticipated. However, the tradeoff can be higher temperatures and the net result is similar heat indices. Will maintain headlines as is as Thursday and Friday are expected be the highest temperatures days of the week. .LONG TERM.../Thursday night through Wednesday/ Issued at 352 PM CDT Wed Jul 19 2017 The aforementioned boundary will begin to lift northward Thursday night into Friday. Expect most of the thunderstorm development to hold off until Thursday night as a shortwave trough approaches from the west and LLJ increases with the focus for the storms mainly over northern Iowa. Storms with possible severe weather will be possible into Friday as the shortwave trough moves along the Iowa and Minnesota border. A stronger shortwave moving across southern Manitoba and Ontario will slowly push a cold front through the state on Saturday. However, rainfall looks quite limited despite the front. This is due to warm air aloft with 700mb temperatures of 11- 13C persisting that will keep the atmosphere mostly capped while the cooler air will be shallow. Depending on the speed of the front, future amendments to the heat headlines may need to be considered. Cooler air will continue to filter in on Sunday with seasonable temperatures lasting into early next week as high pressure moves through the western Great Lakes. As the high moves away, return flow will bring chances for storms back into the state. && .AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/ Issued at 1224 PM CDT Wed Jul 19 2017 Main focus is on thunderstorm chances at KMCW with complex of thunderstorms moving southeastward through SE SD likely to move toward KMCW by mid afternoon. Highlighted potential timing with a VCTS and will refine as storm track becomes more apparent. High winds and hail potential with the complex of storms. Could see MVFR CIGs at KMCW with the storm potential and low level CU field developing currently as well. Otherwise overall threat of thunderstorms limited at the TAF sites through the period, with southerly winds becoming more light and variable to southwesterly into Thursday. && .DMX WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM CDT Saturday for IAZ033>035-044>050- 057>062. Excessive Heat Warning until 8 PM CDT Saturday for IAZ070>075- 081>086-092>097. && SHORT TERM...Ansorge LONG TERM...Ansorge AVIATION...Beerends
Hazardous Weather Outlook National Weather Service Des Moines IA 324 PM CDT Wed Jul 19 2017 IAZ070>075-081>086-092>097-201000- Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas- Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 324 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight An Excessive Heat Warning is in effect for the area through Saturday. Please refer to the National Weather Service website at weather.gov/desmoines for further details. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday An Excessive Heat Warning remains in effect for the area through Saturday. Please refer to the National Weather Service website at weather.gov/desmoines for further details. An isolated thunderstorm is possible Friday night through Sunday. An isolated storm may occur. .SPOTTER INFORMATION STATEMENT... Spotter activation is not likely at this time. IAZ023>028-036>039-201000- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Hamilton-Hardin- Grundy-Black Hawk- 324 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight An isolated strong to possibly severe thunderstorm is possible late tonight. Damaging winds would be the main severe threat, with a secondary threat of large hail. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Additional thunderstorms are possible Thursday night through Sunday. A few severe storms and locally heavy rainfall are possible. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed at times this week. IAZ033>035-044>050-057>062-201000- Sac-Calhoun-Webster-Crawford-Carroll-Greene-Boone-Story-Marshall- Tama-Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek- 324 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight A Heat Advisory is in effect for the area through Saturday. Please refer to the National Weather Service website at weather.gov/desmoines for further details. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday A Heat Advisory remains in effect for the area through Saturday. Please refer to the National Weather Service website at weather.gov/desmoines for further details. A few thunderstorms are possible Thursday night through Friday night and again Sunday. A severe storm is possible. .SPOTTER INFORMATION STATEMENT... Spotter activation is not likely at this time. IAZ004>007-015>017-201000- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- 324 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Thunderstorms are possible through early evening and again late tonight. A few severe storms are possible. Half dollar sized hail, damaging wind gusts in excess of 70 mph and isolated tornadoes are all possible through early evening. The threat of severe weather is lower late tonight, with damaging winds and possibly large hail the main threats. Locally heavy rainfall may also occur. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Additional thunderstorms are possible Thursday night through Sunday. A few severe storms and locally heavy rainfall are possible. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed through early evening, and at later times this week. MJB
The Minneapolis radar (KMPX), 174 km away, was scanning. The volume nearest the first event began at 20:57 UTC.
21 thunderstorm wind. Local standard time, as filed.
Trained spotter estimated winds at 60 to 65 mph. Also report lots of small tree branches down.
Public relayed pictures via twitter of trees snapped and other tree damage in the Ledyard area. Time estimated by radar and this is a delayed report.
County dispatch reported trees and power lines down. This is a delayed report and times is estimated from radar.
County dispatch reported multiple trees down and power line damage in town. This is a delayed report and time estimated from radar.
Trained spotter reported an evergreen tree uprooted in their yard. This is a delayed report and time estimated from radar.
County dispatch reported multiple broken windows, power lines down, and trees downed in town. Time estimated from radar and this is a delayed report.
County dispatch reported multiple trees down and power line damage in town. This is delayed report and time estimated from radar.
County dispatch reported trees down in town. This is a delayed report and time estimated from radar.
County dispatch reported trees down and power outages in town. This is a delayed report and time estimated from radar.
County dispatch reported overturned semis along I-35 around mile markers 203, 205, 207, and 208. This is a delayed report and time estimated from radar.
Forest City Airport AWOS recorded a 66 mph wind gust.
Emergency manager reports semis blown over on I-35 near Highway 9. This is a delayed report and time estimated from radar.
Dispatch reported numerous trees down and power lines down. This is a delayed report and time estimated from radar.
County dispatch reported a transformer blown, power lines and power poles down, and tree damage. This is a delayed report and time estimated from radar.
County dispatch reported significant tree damage in town. This is a delayed report and time estimated from radar.
Iowa DOT RWIS in Hanlontown recorded a 60 mph wind gust.
Emergency manager reported trees down in Manly. This is a delayed report and time estimated from radar.
Mason City Municipal Airport recorded a 63 mph wind gust.
Emergency manager reported multiple locations with trees down in Mason City. This is a delayed report and time estimated from radar.
Amateur radio operator reported trees down in Plymouth. Report came through social media. Time estimated from radar.
KWWL reported via twitter of trees and power lines down in Sumner. Time estimated from radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2017Every state in 2017This day in weather historyWarnings in Iowa, July 2017
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: 711506, 711507, 711508, 711509, 711510, 711511, 711512, 711513, 711514, 711515, 711516, 711517, 711518, 711519, 711520, 711521, 711522, 711523, 711524, 711525, 711526.