During the evening of the 9th strong to severe storms initiated in parts of southern and western Minnesota near a surface low pressure center and attendant boundary and proceeded to move SE towards Iowa. Eventually, prior to their entry into northern Iowa, the storms generally congealed and formed an MCS and rode the MUCAPE gradient S/SE into northern Iowa and produced numerous damaging wind…
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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 DMX wrote it up.
During the evening of the 9th strong to severe storms initiated in parts of southern and western Minnesota near a surface low pressure center and attendant boundary and proceeded to move SE towards Iowa. Eventually, prior to their entry into northern Iowa, the storms generally congealed and formed an MCS and rode the MUCAPE gradient S/SE into northern Iowa and produced numerous damaging wind reports and a couple for severe hail in the hours after midnight/early morning on the 10th. The general environment was highly supportive for strong storms with MUCAPE values in excess of 2000 J/kg, and effective bulk shear in excess of 50 kts.
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 9, 11:02 PM CST, 3 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 1202 AM CDT Mon Jul 10 2017 ...Updated Aviation Discussion... .SHORT TERM.../Tonight through Monday/ Issued at 319 PM CDT Sun Jul 9 2017 As a mid-level shortwave drops southeast across MN and WI, height falls and associated lift will result leading to showers and storms across the upper midwest. With decent instability and shear severe potential is expected with many of these storms across MN and WI. This shortwave will also bring showers and thunderstorms overnight to northeastern and east central Iowa. Main concerns as far as severe weather in the northeastern portion of our CWA overnight are damaging winds and possibly small hail. Locally heavy rainfall will also be possible within stronger storms. Confidence for severe potential over the northeastern part of the CWA is low. By the early morning hours, the shortwave will move off to the east with a ridge of high pressure beginning to build in behind it. Storms are expected to initiate by early evening along a boundary across central MN associated with an area of low pressure over central SD. Area of storms expected to develop into an MCS with a bow echo type line of storms moving through northeast IA likely clipping northeastern portions of the forecast area. Storm chances to push south and east through the state as the area of low pressure over SD drops southeastward through the period. The associated boundary will sink southward through Iowa tonight into Monday. Low confidence on where this boundary will get hung up, with the potential from central IA southward into northern MO. Areas to the south of this boundary will be hot and humid, with chances for pop- up afternoon thunderstorms expected near the boundary Monday afternoon. As an area of high pressure builds southward, this should push the boundary further south along with the thunderstorm chances as well, thus have the highest pops further south along the IA/MO border toward early evening. Temperatures likely to push into the lower to mid 90s across the south where very warm air will be in place south of the aforementioned boundary. Additionally moisture will be increasing across the state and pooling along the boundary with dewpoints pushing up into the lower 70s. This will send heat index values into the low 100s. At this time heat index values approach heat advisory criteria, but will refrain from issuing given the uncertainty with the boundary placement and potential for storms in the area through the afternoon hours as well. .LONG TERM.../Monday night through Sunday/ Issued at 319 PM CDT Sun Jul 9 2017 Potentially active period depending on where boundaries end up and which model you believe. In the big picture, the upper ridge flattens over the Upper Midwest allowing for a series of fast moving shortwaves to pass across the region. At the surface, a low over the Plains will slowly drift east through Wednesday. A frontal boundary will extend from the low southeastward across the Upper Midwest. The location of this boundary will be key as to the exact location of the biggest storms/heaviest rainfall. Medium range models all vary a bit on the location of this front, ranging from northern MO into southern IA. South of this boundary will also be oppressive heat and humidity whereas along and north of it...not as bad. Monday night...The frontal boundary Monday night looks to be in far Southern IA and as a result locations everywhere but the far south, while hot, should fall below heat advisory. Thunderstorms are probable along and South of the front and should be severe as well as heavy rain producers. PWAT's in this area approach/exceed 2 inches. Deep shear is somewhat questionable at least with the GFS but given the instability and the location of the boundary, should be sufficient for severe storms with large hail and damaging wind. For a brief period, LCL's are near 800m so cannot rule out a tornadic potential early on but all of this will depend on what happens with the MCS tonight/Monday and what boundaries it lays out and where. Tuesday and Tuesday night the boundary lifts north across the state as a warm front but the surface low shifts into MN so a trailing cold front will enter the far northwest. Additional storms with severe potential/heavy rain will be possible again Tuesday Tuesday night initially from the warm front lifting northeast then later from the cold front entering from the northwest. Needless to say, the instability and shear through the period remain sufficient for strong to severe storms. Heavy rain will still be likely with storms although PWATS by this time are somewhat less...on the order of 1.6 to 1.7 inches (versus 2 inches). Wednesday through Thursday...The surface low finally shifts into the Great Lakes pushing precip east and south of IA however the boundary will still be near southern IA Wednesday so some chance for storms across the south Wednesday. Thursday the front appears to shift south through the day but nor before waffling back north some as the ridge builds back into the rockies. Wednesday and Thursday appear quieter than early in the week. Late Thursday through the end of the forecast period...Ridging over the Rockies increases putting the region back into northwest flow. Temps will be closer to normal but models are having a hard time resolving any shortwave timing and location so pops right now are pretty nebulous. && .AVIATION.../For the 06Z TAFS through 06Z Monday night/ Issued at 1200 AM CDT Mon Jul 10 2017 Storms to impact MCW to ALO and possibly FOD for a short stint. Expect brief MVFR visibility with the heavy rain and gusty winds, possibly severe winds at times. Storms will move east of the area by 10z at the latest. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Beerends/Worley LONG TERM...FAB AVIATION...Podrazik
Hazardous Weather Outlook National Weather Service Des Moines IA 404 PM CDT Sun Jul 9 2017 IAZ004>006-015-016-024>026-036>038-049-050-062-101100- Emmet-Kossuth-Winnebago-Palo Alto-Hancock-Humboldt-Wright- Franklin-Hamilton-Hardin-Grundy-Marshall-Tama-Poweshiek- 404 PM CDT Sun Jul 9 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Tonight Thunderstorms are possible tonight, there is a slight risk for severe storms with damaging winds the main threat. Large hail and a brief tornado are also possible, along with locally heavy rainfall. .DAYS TWO THROUGH SEVEN...Monday through Saturday Strong to possibly severe thunderstorms are possible late Monday night into Tuesday morning. Large hail will be the primary threat. Damaging winds are also possible, along with periods of heavy rainfall. Periodic thunderstorm chances are also forecast late Tuesday through Thursday. The predictability of severe storms remains low at this time. Periods of heavy rainfall cannot be ruled out. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this evening through early tonight. IAZ007-017-027-028-039-101100- Worth-Cerro Gordo-Butler-Bremer-Black Hawk- 404 PM CDT Sun Jul 9 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Tonight Thunderstorms are possible tonight, there is an enhanced risk for severe storms with damaging winds the main threat. Large hail and a brief tornado are also possible, along with locally heavy rainfall. .DAYS TWO THROUGH SEVEN...Monday through Saturday Strong to severe thunderstorms are possible Tuesday into early Wednesday. Large hail will be the primary threat. Damaging winds are also possible, along with periods of heavy rainfall. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this evening through early tonight. IAZ023-033>035-044>048-057>061-070>075-081>086-092>097-101100- Pocahontas-Sac-Calhoun-Webster-Crawford-Carroll-Greene-Boone- Story-Audubon-Guthrie-Dallas-Polk-Jasper-Cass-Adair-Madison- Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello- Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 404 PM CDT Sun Jul 9 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Tonight An isolated strong to severe storm is possible tonight. Large hail or damaging winds would be the main severe threats with any stronger storm that develops. .DAYS TWO THROUGH SEVEN...Monday through Saturday Strong thunderstorms are possible late Monday into Tuesday morning. Large hail will be the primary threat. Damaging winds are also possible, along with periods of heavy rainfall. Periodic thunderstorm chances are also forecast late Tuesday through Thursday. The predictability of severe storms remains low at this time. Periods of heavy rainfall cannot be ruled out. Hot and humid conditions will lead to high heat index values in the afternoon hours Monday into Wednesday. Current heat index values top out in the low 100s. .SPOTTER INFORMATION STATEMENT... Spotter activation is not likely tonight, but may be needed late Monday
The Minneapolis radar (KMPX), 169 km away, was scanning. The volume nearest the first event began at 05:03 UTC.
12 thunderstorm wind, 2 hail. Local standard time, as filed.
Law enforcement reported a tree blown down on a house in Kensett. This is a delayed report and time estimated from radar.
Emergency manager reported trees uprooted and a grain bin blown down in Hanlontown. This is a delayed report and time estimated by radar.
Law enforcement reported trees and power lines down at Crystal Lake. This is a delayed report and time estimated from radar.
Law enforcement reported power lines down on the northwest side of Britt. The is a delayed report and time estimated from radar.
Emergency manager reported significant wind-driven hail damage to corn and bean fields between Britt and Klemme. Golf ball or larger hail and 70 to 80 mph winds pulverized 5 to 6 foot cornstalks to stubble. Trees and power lines also downed.
Storm chaser video depicted extensive wind damage to power poles, including series of snapped poles. This is a delayed report and time estimated from radar.
Storm chaser video depicted extensive wind damage and likely wind driven hail damage in the town of Klemme. Damage included numerous car, home, and business windows broken and trees downed on homes. This is a delayed report and time estimated from radar.
Public reported golf ball sized hail. Time and location estimated from radar.
Trained spotter reported large trees downed from the winds. This is a delayed report and time estimated from radar.
Trained spotter reported golf ball sized hail, also estimated winds at 60 mph.
Trained spotter reported 4 large trees downed from the winds. This is a delayed report and time estimated from radar.
Law enforcement reported power lines down in Latimer. This is a delayed report and time estimated from radar.
Iowa DOT reported power lines down along Highway 63 at mile marker 144. Time estimated from radar.
Law enforcement reported power lines blown down onto a semi trailer. This is a delayed report and 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: 711467, 711468, 711469, 711470, 711471, 711472, 711473, 711474, 714593, 711475, 711476, 711477, 711478, 711479.