Ahead of a cold frontal boundary temperatures throughout Iowa were able to reach into the upper 80s to around 90 along with dew points into the mid 60s. Along with accompanying vertical temperature profiles, MUCAPE values were able to reach into the 3000+ J/kg neighborhood in many spots with low end supportive effective shear around 30-35 kts initially.
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.
Ahead of a cold frontal boundary temperatures throughout Iowa were able to reach into the upper 80s to around 90 along with dew points into the mid 60s. Along with accompanying vertical temperature profiles, MUCAPE values were able to reach into the 3000+ J/kg neighborhood in many spots with low end supportive effective shear around 30-35 kts initially. As storms triggered in eastern and southeastern Nebraska, they quickly merged into a series of MCSs and tracked northeast into Iowa. The strongest storms predominantly were located northwest of the Des Moines metro roughly along a line from Omaha to Mason City. Numerous severe wind gusts in excess of 60 mph were reported along with wind damage and occasional severe hail.
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 May 16, 5:34 AM CST, 26 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 634 AM CDT Tue May 16 2017 .SHORT TERM.../Today through Tonight/ Issued at 326 AM CDT Tue May 16 2017 08z Satellite and sfc obs analysis depicts a somewhat disorganized, fast-moving shortwave passing north- northeastward through Nebraska this morning...making it into north-central Minnesota by this afternoon. Pressure gradient tightens to around 3mb/110 km. With no additional localized wind- boosting mechanisms of note, winds should stay below advisory criteria. Strong southerly winds to boost WAA once again. Overall, have kept max temps for today close to where they were yesterday. Severe threat mainly confined to western/northwestern Iowa...with an arrival time in the 00z Wed - 03z Wed timeframe. Models in good agreement with attendant boundary to the aforementioned shortwave draping through this area to serve as focusing mechanism. MLCape values reach 2500 J/kg. Low-level lapse rates reach 8 C/km. DCAPE values exceed 1000 j/kg...with the highest values seeming placed well to our west. In all, tornado parameters not too impressive...so primary svr mode will be large hail, with damaging winds as a distant secondary threat. Additionally...PWATs look to exceed 1.65 inches per the GFS. Interpolating between KOAX and KMSP on the SPC climatology page, this value would be near the top of the charts. In short, heavy rainfall is possible and flash flooding cannot be ruled out...though NW Iowa can typically handle higher rainfall amounts better than most other portions of the DMX CWA. .LONG TERM.../Wednesday through Monday/ Issued at 326 AM CDT Tue May 16 2017 Wednesday PM-Thursday PM... Conditional svr threat, but if storms become severe, mini-outbreak cannot be ruled out. Models coming into good agreement with pushing parent upper low located near the Four Corners region of the CONUS at 09z Tue, to the upper Midwest. By 00z Thu, models place this upper low over the IA/SD/MN/NE area. with sfc low slightly lagging to the south. As of now, central to SE Iowa looks to be the focus for the potentially worst weather. 0-3km Bulk shear values approach 50 kts, which is off the charts. 0-6km MUCape is only 1000 J/KG which is not great, but sufficient. Tornado setup is what could be interesting. LCL heights below 1000m, KDSM and KOTM hodographs very much "sickle-shaped", 0-1km helicity approaching 200 m2/s2. Top 15 CIPS analog events tend to show a few tornadoes, damaging wind reports, and isolated large hail reports basically along and east of I-35, along and south of I-80... which seems reasonable. Much uncertainty, however, as to how morning/early afternoon will pan out with cloud cover + ongoing rain possible. Next forecast discussion should pin down a little better... if timing lines up, SPC upgrade to enhanced- moderate risk cannot be ruled out in our southeast. Friday into the weekend... Another slow-moving upper low/broad longwave trough will dig through the Plains states. 00z Tue GFS and ECMWF in good agreement with reinforcing moisture making it into Iowa...raising PWATs into the 1.25 to 1.5 inch range through Saturday. 850mb temps drop to around +10C by Saturday...so with cloud cover and rain potential, highs will struggle to make it into the 60s...a stark contrast from 90 degree wx yesterday and today. Thunder potential there, though svr threat not impressive at this time. && .AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/ Issued at 634 AM CDT Tue May 16 2017 Strong south surface flow is expected today with widespread VFR conditions. Ceilings will be at or above 12kft through today with unrestricted visibilities. Showers and thunderstorms will move into the state tonight with MVFR to IFR conditions in vicinity of the storms. Winds will remain from the south overnight but not as strong. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Kotenberg LONG TERM...Kotenberg AVIATION...Cogil
Hazardous Weather Outlook National Weather Service Des Moines IA 458 AM CDT Tue May 16 2017 IAZ004>007-015>017-023>026-033>036-044>047-057>059-070>072-081- 082-092-093-171000- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Sac-Calhoun-Webster-Hamilton- Crawford-Carroll-Greene-Boone-Audubon-Guthrie-Dallas-Cass-Adair- Madison-Adams-Union-Taylor-Ringgold- 458 AM CDT Tue May 16 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Strong to severe thunderstorms are possible this evening into tonight. Large hail will be the primary threat, with damaging winds a secondary threat. Flash flooding/periods of heavy rainfall cannot be ruled out at this time. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorms are likely Wednesday. A few storms may be strong, with severe weather potential not ruled out. All modes of severe weather are possible. Non-severe thunderstorms are possible Friday through Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this evening into tonight. Spotter activation cannot be ruled out for Wednesday. IAZ027-028-037>039-048>050-060>062-073>075-083>086-094>097-171000- Butler-Bremer-Hardin-Grundy-Black Hawk-Story-Marshall-Tama-Polk- Jasper-Poweshiek-Warren-Marion-Mahaska-Clarke-Lucas-Monroe- Wapello-Decatur-Wayne-Appanoose-Davis- 458 AM CDT Tue May 16 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Strong thunderstorms are possible late this evening into tonight. Though it cannot be ruled out, the threat for severe weather is low at this time...with large hail the main threat and damaging winds a secondary threat. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Strong to severe thunderstorms are possible Wednesday. The primary threat will be isolated tornadoes, with damaging winds a secondary threat, and large hail a possibility. As of now, the greatest threat for severe weather will be in southeastern Iowa. Non-severe thunderstorms are possible Friday through Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not likely this evening into tonight, but may be needed Wednesday. Kotenberg
Special Weather Statement National Weather Service Des Moines IA 442 AM CDT TUE MAY 16 2017 IAZ004-005-015-161100- Palo Alto IA-Kossuth IA-Emmet IA- 442 AM CDT TUE MAY 16 2017 ...Strong winds expected in far northern Iowa early this morning... At 439 AM CDT, several reports of strong wind gusts in northwest Iowa had been received. These winds are expected to impact locations in Palo Alto, Emmet and Kossuth county through 6 AM. Wind gusts up to 55 mph can be expected. Locations impacted include... Estherville, Emmetsburg, Swan Lake, Armstrong, Graettinger, Ruthven, Swea City, Ringsted, Wallingford, Ayrshire, Ledyard and Gruver. LAT...LON 4350 9398 4293 9491 4350 9491 TIME...MOT...LOC 0939Z 228DEG 36KT 4368 9528 4325 9508 4292 9507 Cogil
The Des Moines radar (KDMX), 136 km away, was scanning. The volume nearest the first event began at 12:00 UTC.
42 thunderstorm wind, 6 hail, 1 heavy rain. Local standard time, as filed.
Coop observer recorded heavy rainfall of 2.24 inches over the last 24 hours.
Emergency manager reported golf ball sized hail in the city of Manilla.
Trained spotter reported wind gusts up to 70 mph.
Local fire department reported 60 to 70 mph wind gusts.
Trained spotter reported at least 3 large trees down in their neighbor's yard. Time estimated by radar and previous reports.
Carroll AWOS reported sustained winds of 48 mph and gusts to 71 mph.
Large tree branches down in the yard.
Public reported quarter sized hail in Fonda.
Amateur radio operator reported wind gusts to 60 mph. Time estimated by radar.
Trained spotter reported quarter sized hail.
Trained spotter reported wind gusts to 60 mph.
Rockwell City RWIS recorded 73 mph wind gust.
Trained spotter reported strong winds and heavy rainfall. Many streets in town had tree branches down ranging from small sticks to big, round branches. A tree was snapped at one of the cemeteries on the east side of town. Standing water throughout town.
Amateur radio operator reported wind gusts to 60 mph.
Public reported strong winds, blowing dust, and a tree had fallen on a car.
Trained spotter reported a metal garage destroyed.
Amateur radio operator reported a transformer blown down/over.
Amateur radio operator reported wind gusts to 70 mph.
Trained spotter reported tree limbs down in Manson. Size unknown at the time.
Trained spotter reported lots of tree damage. Sizes unknown at the time.
Trained spotter reported widespread power outages, upwards of 40 foot tall trees down, and estimated at least 70 mph winds. This is a delayed report.
Trained spotter reported pea sized hail. Numerous large trees are down all across the city. More detailed damage report in similarly time stamped LSR.
Trained spotter reported multiple tree limbs down along with a few transformers throughout town. Power out in many locations.
Emergency manager reported a 4-plex apartment building had its roof blown off. Time estimated by radar.
Amateur radio operator reported 6 inch diameter tree limbs down and blocking the road.
A 50.2 kt gust was recorded by the Fort Dodge RWIS station.
A trained spotter reported quarter sized hail.
Widespread tree limbs down and a few trees in town. South of town a windmill was bent over and a residential TV/Radio tower was bent over, and grain bins were bent in as well.
Trained spotter reported a window blown in at their home. Estimated 60 to 70 mph winds.
Numerous downed trees some up to 18 inches in diameter across the county, some buildings damaged and numerous power lines down. A railroad crossing arm was snapped off and a garage was destroyed in Whittemore, some outbuildings and a house were damaged near town as well. Agricultural impacts as well with machinery blown over, bent up and also seed loss.
Trained spotter reported 5 to 6 inch diameter tree limbs down.
Trained spotter estimated wind gusts to around 60 mph ongoing at the time.
Trained spotter reported wind gusts around 55 to 60 mph along with pea sized hail. Several tree limbs down roughly 2 to 3 inches in diameter.
Algona RWIS measured wind gusts to 70 mph.
Trained spotter reported several tree limbs of various size down and one large tree about 5 to 6 feet in diameter down. Numerous power outages as well. Time estimated by radar.
Trained spotter reported strong winds, including tree branches down, wind broken out, and power out. No estimate on wind speed at the time.
Trained spotter reported wind gusts to around 70 mph.
Trained spotter reported quarter sized hail ongoing at the time of the report.
Clarion AWOS reported 48 mph winds with gusts to 60 mph.
Emergency manager reported gusts to 60 mph along with nickel sized hail and heavy rainfall.
Iowa DOT reported debris blocking the roadway in both directions on Highway 69. Time estimated by radar.
Public reported shingles on the road, trees and branches down in Garner. Time estimated by radar.
Trained spotter reported wind gusts to around 60 mph in the downtown area. Power out as well.
Emergency manager reported multiple tree limbs down throughout the town of Mason City. Some have fallen on power lines or are blocking roads. A few power poles snapped as well. Power out in multiple locations. Time estimated by radar.
Coop observer reported quarter sized hail.
Trained spotter measured a 71 mph wind gust at their home.
Coop observer reported wind gusts to 65 mph.
Emergency manager reported numerous trees downed along with power lines down. A tree fell on a house in town.
Emergency manager reported trees downed in Knoxville. One fell on a car and crushed it.
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, May 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: 695316, 695262, 695263, 695264, 695265, 695267, 699714, 695268, 695270, 695271, 695272, 695273, 695274, 695275, 695277, 698041, 695278, 695280, 695281, 695282, 695284, 695285, 695287, 695288, 695289, 695917, 695291, 698042, 695292, 699920, 695293, 695294, 695295, 695296, 695297, 695299, 695300, 695301, 695303, 695304, and more.