A broad area of low pressure was situated across much of Nebraska and Kansas during the morning hours and slowly made its way east, northeast through the day. Much of Iowa was in the warm sector throughout the day, resulting in modest temperatures into the mid and upper 70s and dew points to the low 60s.
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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.
A broad area of low pressure was situated across much of Nebraska and Kansas during the morning hours and slowly made its way east, northeast through the day. Much of Iowa was in the warm sector throughout the day, resulting in modest temperatures into the mid and upper 70s and dew points to the low 60s. Thermodynamic soundings were not substantial, confirming elevated threat with a sizable cap and MUCAPE values in the 1000-1500 range. As a result, generally isolated to local convection was seen with nearly all severe reports of the hail variety.
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 Apr 9, 5:43 PM CST, 1 hour 35 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 643 PM CDT Sun Apr 9 2017 .SHORT TERM.../Tonight through Monday/ Issued at 320 PM CDT Sun Apr 9 2017 Not much change to the forecast in regards to thunderstorm potential for this evening and tonight. Shortwave trough is evident on water vapor over Wyoming and beginning to take on a negative tilt as it pivots northeast. 20z mesoanalysis has the surface low south/southeast of Sioux City near the NE/IA border with a warm front stretching through northwest Iowa and into southern Minnesota, a dry line southward into central Kansas, and cold front trailing behind through southeast Nebraska and into northwest Kansas. Southerly flow to the south of the warm front continues to advect moist air northward, beneath a substantial EML and strengthening mid-level cap. The best chances for any convection this evening will be near along and north of the warm front. The boundary should provide enough lift break the cap, above which steep mid- level lapse rates of 8-9 C/km and effective layer shear above 40 kts will be sufficient to support a risk for large hail and strong wind gusts. The tornado threat has been dwindling through the day as more hi-res model runs favor elevated convective initiation on the northern side of the front. Any tornado threat would need to be along or near the front this evening, particularly in the area of the triple point in northwest Iowa. Further south through central and southern Iowa, it looks likely that the atmosphere will remain capped with respect to surface based convection until near or after dark when the dry line moves east into the state and begins to be overtaken by the cold front. Another burst of low level theta-e advection by means of a strengthening LLJ will support MUCAPE of 1000-2000 J/KG into the overnight hours, which will be readily available for any convection and support a risk for large hail and damaging winds. Discrete/multi-cells are possible initially, but mean flow parallel the the surface boundary should favor linear storm modes. Shortwave trough pushes east toward the Great Lakes region on Monday. Modest pressure rises on the backside of the departing surface low will favor breezy northwest winds and cooler temperatures, especially in northwest Iowa where highs may be more than 20 degrees cooler than today. A few showers are also possible as moisture wraps around the northern side of the low. Previous forecast with POPs generally along and north of Highway 20 still in line with latest model guidance. .LONG TERM.../Monday night through Sunday/ Issued at 320 PM CDT Sun Apr 9 2017 Upper level system impacting the region today will slowly meander eastward cutting off across Iowa Monday and then pushing east into Wisconsin Monday night. Expect some lingering low clouds and precip chances across the north Monday evening, before rain moves out late Monday night. High pressure builds into the region Tuesday with a zonal flow pattern aloft. Shortwave energy moving eastward from the Rockies Wednesday begins to dig a little across the central US with southerly flow off the gulf picking up ahead of the upper level wave. Could see a quick shot of showers/storms move through the state later Wednesday into Wednesday night before the system drops southeastward out of the region. Stronger trough to move ashore in the Pacific NW late in the week. This system pushes eastward across the Rockies and through the central US/Canada toward the weekend. A warm front will lift northward ahead of this system, with precip chances initially late Thursday into Friday. The cold front with the system ejecting from the Rockies will sweep through Iowa later Friday and stall out across the area into the weekend. GFS/EC differ on the track of the system eastward from the Rockies with the GFS a bit further north. Overall differences do not amount to much of a difference for precip chances across the state at this time. As for temperatures through the period appear to remain near or above the seasonal averages. && .AVIATION.../For the 00Z TAFS through 00Z Monday evening/ Issued at 643 PM CDT Sun Apr 9 2017 Trof axis will pass through Iowa tonight with surface winds switching from the south southwest to the west northwest overnight. Isolated to scattered storms will be possible late this evening into the early morning hours before the threat subsides. Ceilings may fall to MVFR in the north late tonight into Monday morning in northern Iowa but should remain VFR in central and southern Iowa. Only visibility restrictions will be with any storms that pass through Iowa tonight. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Martin LONG TERM...Beerends AVIATION...Cogil
Hazardous Weather Outlook National Weather Service Des Moines IA 356 PM CDT Sun Apr 9 2017 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-102100- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- 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-Adams-Union- Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne- Appanoose-Davis- 356 PM CDT Sun Apr 9 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Strong to severe thunderstorms are possible this evening into the overnight hours tonight. The greatest severe threat will be west of Interstate 35 with large hail and damaging winds the primary concern. However, an isolated tornado or two cannot be completely ruled out. .DAYS TWO THROUGH SEVEN...Monday through Saturday Additional thunderstorms are possible Wednesday into early Thursday and again Friday afternoon into early Saturday. However, the risk of severe weather appearing low at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed. KLP
The Des Moines radar (KDMX), 105 km away, was scanning. The volume nearest the first event began at 01:18 UTC.
23 hail, 1 thunderstorm wind. Local standard time, as filed.
Trained spotter reported up to nickel sized hail as the storm quickly developed. Hail was very brief.
Coop observer reported half dollar sized hail. This is a delayed report.
Emergency manager relayed a report of nickel sized hail in Clear Lake.
Emergency manager reported mostly quarter sized hail with a few stones slightly larger.
Trained spotter reported hail ranging from dime to quarters in size.
Trained spotter reported lots of hail over the last few minutes and ongoing up to quarters in size.
Trained spotter reported dime to nickel sized hail.
Emergency manager relayed reports of quarter sized hail just south of Manly on Highway 65.
Local fire department employee reported up to quarter sized hail 2 N of Plymouth.
Trained storm spotter reported mostly quarter sized hail with a couple of stones measuring up to an inch and a half.
Trained spotter reported nickel to quarter sized hail ongoing in the Mason City area.
Trained spotter reported quarter sized hail. Time estimated by radar and report from social media.
Trained spotter reported up to half dollar sized hail. This is a delayed report.
Coop observer reported quarter sized hail. This is a delayed report.
Emergency manager reported trees down on a vehicle along with roof and building damage. This is a delayed report.
Trained spotter reported up to quarter sized hail. This is a delayed report.
Emergency manager reported quarter sized hail.
Trained spotter reported up to quarter sized hail.
Trained spotter reported up to quarter sized hail.
Law enforcement reported quarter sized hail.
Trained spotter reported half dollar sized hail.
Trained spotter reported up to half dollar sized hail.
Public reported quarter sized hail measured at Red Rock Dam at 535z. This report is a delayed report and came from KCCI social media.
Public report of half dollar sized hail via KCCI on social media.
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, April 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: 687268, 687269, 687273, 687274, 687275, 687276, 687277, 687278, 687279, 687280, 687281, 687282, 687283, 687267, 687284, 687287, 687288, 687289, 687290, 687291, 687292, 687285, 687293, 687294.