After a complex of storms moved through the state in the early morning hours of the 28th, producing a smattering of sub-severe to severe hail, the area found itself entrenched firmly within the warm sector of a low pressure system passing to the northwest. Resulting MLCAPE values during the afternoon and early evening were in the 2000-3000 J/kg range, along with effective bulk shear around 40-50…
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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.
After a complex of storms moved through the state in the early morning hours of the 28th, producing a smattering of sub-severe to severe hail, the area found itself entrenched firmly within the warm sector of a low pressure system passing to the northwest. Resulting MLCAPE values during the afternoon and early evening were in the 2000-3000 J/kg range, along with effective bulk shear around 40-50 kts, LCL heights under 1000 m, and semi-supportive 0-1 km helicity around 100 m2/s2. With such an environment, parameters such as the sig tor (effective layer) highlighted large portions of Iowa during the afternoon and evening hours. Resulting storms quickly went supercellular and proceeded to produce multiple tornadoes and large hail in excess of 2.5 inches throughout central and southwest Iowa. Seven tornadoes occurred across mainly rural portions of southwest into central Iowa in this event. The longest tornado was an EF1 tornado that touched down in Warren County and crossed into Marion County that was on the ground for over 17 miles. Much of the tornado moved through rural portions of Warren and Marion Counties, but one farmstead received damage along the Warren/Marion County line with additional light damage to rural residences in Marion County. A large wedge EF2 tornado touched down in Taylor County moving through mainly rural areas. One outbuilding was nearly destroyed and minor damage was done to a house.
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 Jun 27, 10:52 PM CST, 3 hours 39 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 1152 PM CDT Tue Jun 27 2017 .SHORT TERM.../Tonight through Wednesday/ Issued at 158 PM CDT Tue Jun 27 2017 The primary concern through the period will be convective trends into Wednesday as an MCS is expected to develop across the High Plains and reach Iowa during the early morning hours Wednesday. There will be a pronounced regime change heading into this with a return to more seasonal temperature and humidity levels in just a short amount of time. Dewpoints may rise 20+F in 12-14 hours in many locations. Sharply increasing warm/theta-e advection will advance through Iowa this evening, but initially be moisture starved with little sensible weather. However kinematic forcing ahead the current WY/MT short wave will work with persistent Plains return flow to moisten our upstream airmass and feed MCS development. MUCAPEs should be 1500-3000 j/kg into early tomorrow morning west. This diminishes by 09z however which supports the west to east gradient noted in the SPC Day 1 outlook and 3hr Calibrated Severe Probs per the 09z SREF. 35-50kts of inflow per 300-305K isent surfaces will support the MCS in some form into the night however, likely based on shallow convergence and outflow with some suggestions that the synoptic warm front will try to surge to northern Iowa or farther north. It will not take much to get re-generation by tomorrow afternoon however with most models suggesting uncapped 2000-3000 j/kg MLCAPEs and 35-45kt of 0-6km shear favorably oriented to the approaching boundary for discrete cells or at least small clusters. This will support all modes of severe weather, most likely over central and southeast sections, and fully expect current SPC Day 2 Slight Risk to be upgraded once confidence in location can be better pinned down after overnight outflow shows its hand. One interesting note is that the convection allowing model ARW cores are less aggressive than one might expect per the aforementioned shear and instability based on updraft helicity vs NMM cores, which are often on the higher end anyways. Thus there is still some uncertainty with the tornado potential versus more likely damaging wind and hail. If local outflow does not favorably augment 0-1 SRH the general synoptic regime, broad SW low level flow, would seem to be less favorable for tornadoes. .LONG TERM.../Wednesday night through Tuesday/ Issued at 158 PM CDT Tue Jun 27 2017 The potential for additional strong to severe thunderstorms Wednesday night through Thursday is the focus of the extended forecast. Thunderstorm development Wednesday night will be ongoing near a cold front extended from northeast to southwest Iowa. Ahead of the front, an unstable airmass is expected with forecast models progging MU CAPE values over 2500 j/kg along with a strengthening and veering low level jet near 30-50 knots. Numerous strong to severe thunderstorms will develop along this boundary during the evening and overnight hours aided by the passage of a shortwave in zonal flow aloft. Damaging winds, large hail, heavy rain and a few tornadoes within a few hours of initiation will be possible. The surface front looks to become parallel to the zonal flow overnight Wednesday into Thursday morning shifting the focus for showers and thunderstorms and heavy rain to southern Iowa. Surface low deepens on Thursday across Kansas in response to a deepening upper trough over the Dakotas with favorable moisture transport over east west oriented surface boundary. Another round of strong to severe thunderstorms will develop with shortwave kicking ahead of a deepening upper trough. Along with heavy rain, all modes of severe weather will be possible including tornadoes with thunderstorm development near the front. Thunderstorms will end west to east across the state Friday with boundary exiting into the Mid-Mississippi Valley. The upper trough digs over the Midwest Saturday. Northwest winds will increase with windy conditions expected from strong mixing. A few showers and thunderstorms will be possible over northern Iowa Saturday afternoon and evening aided by daytime heating and another shortwave rotating around the base of the upper low. Next week, the pattern shifts to northwest flow aloft over Iowa with an upper ridge building over the Rockies. Could see another round of showers and thunderstorms on Monday before warmer and drier weather returns. && .AVIATION.../For the 06Z TAFS through 06Z Wednesday night/ Issued at 1152 PM CDT Tue Jun 27 2017 Showers and storms still expected to move through much of the state tonight, with the activity expected across the south pushing slower across NE than previously expected. Therefore have adjusted timing. Should see additional activity by late afternoon so have highlighted with VCTS or VCSH depending on greater confidence and where better chance for thunder expected. Low level wind shear still possible through sunrise especially across the western sites, then gusty south to southwesterly winds expected Wednesday. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Small LONG TERM...Angle AVIATION...Beerends
Hazardous Weather Outlook National Weather Service Des Moines IA 334 PM CDT Tue Jun 27 2017 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-282045- 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- 334 PM CDT Tue Jun 27 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Strong to potentially severe thunderstorms are forecast to develop over western portions of Iowa after midnight and will spread eastward Wednesday morning. Large hail and damaging winds look to be the primary threat, but an isolated tornado or two cannot be completely ruled out. Locally heavy rain is also possible. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Thunderstorms Wednesday morning are likely to diminish in coverage and intensity across eastern portions of Iowa after sunrise. A second round of strong to severe storms will develop by the afternoon over central to western Iowa. Large hail, damaging winds and even a few isolated tornadoes are possible. Additional strong to severe thunderstorms are forecast Thursday night into Friday. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible late tonight and likely again Wednesday afternoon.
The Des Moines radar (KDMX), 27 km away, was scanning. The volume nearest the first event began at 08:29 UTC.
27 hail, 10 funnel cloud, 9 tornado, 5 thunderstorm wind. Local standard time, as filed.
Emergency manager reported nickel to quarter sized hail along with estimated 40-45 mph wind gusts.
Trained spotter reported a funnel cloud.
Public reported golf ball sized hail.
Trained spotter reported mostly dime sized hail, but some quarter sized mixed in.
Fort Dodge Airport ASOS recorded a 59 mph wind gust.
Trained spotter reported nickel sized hail.
Path was intermittent for several miles after developing with condensation funnel not always visible. However, a persistent funnel eventually formed and was well documented as it moved across northern Adair County. It remained in rural areas with only minor damage to a few outbuildings and trees.
Tornado tracked across rural areas northwest of Carbon. Some minor damage occurred to outbuildings with most of the damage occurring to trees along the path.
Trained spotter reported a funnel cloud.
Trained spotter reported large limbs snapped off a tree.
A weak tornado passed through rural areas of Adams county north of Prescott. Very minor tree damage was observed at one rural house. Tornado was captured on video by the public.
Tornado developed in eastern Adair County and traveled through rural areas before entering Madison County. There was minor damage to one property and impressive tree damage along the Adair/Madison County line.
Media relayed public report of baseball sized hail. This is a delayed report via social media.
Trained spotter reported quarter sized hail.
Trained spotter reported golf ball sized hail.
Tornado entered Madison County from Adair County. There was impressive tree damage just inside Madison County as the tornado moved northeast. Little additional damage was noted for the rest of the path.
Large wedge tornado moved across southern Taylor County. The tornado remained in rural areas with primarily tree and crop damage. A few structures were also hit with some minor damage to a house and one old outbuilding nearly destroyed. Most intense damage occurred in the later half of the tornado path where EF2 damage was observed as 4 large wooden electrical power line towers where destroyed along with decimating a nearby grove of trees.
Media reported baseball sized hail.
Public reported half dollar sized hail.
Law enforcement reported golf ball sized hail.
Trained spotter reported a tree snapped off near the Warren/Madison County line.
Trained spotter reported baseball sized hail. This is a delayed report.
Amateur radio operator reported quarter sized hail.
Public reported quarter sized hail.
Public reported nickel sized hail.
Trained spotter reported a funnel cloud.
Public reported half dollar sized hail.
Public reported quarter sized hail.
NWS employee reported quarter sized hail.
Trained spotter reported a funnel cloud.
Public reported quarter sized hail.
Trained spotter reported six inch diameter tree branches down.
Public reported a funnel cloud.
Public reported nickel sized hail.
Public reported a funnel cloud.
Tornado developed in far eastern Warren County and hit a farmstead along the county line road with Marion County, producing EF1 damage at the site. The tornado then moved into Marion County.
Tornado moved into Marion County from Warren County. The tornado remained in rural portions of the county south and east of Pleasantville with the tornado lifting just southwest of Otley. Several rural residences received light damage with much tree damage along the path.
Media relayed report of half dollar sized hail via social media.
A brief tornado developed east of New Virginia and moved through a rural field before lifting.
Amateur radio operator reported quarter sized hail.
Trained spotter reported a funnel cloud.
Trained spotter reported a funnel cloud.
Iowa Falls Airport AWOS recorded a 58 mph wind gust.
Trained spotter reported a funnel cloud.
Public reported quarter sized hail via social media.
Trained spotter reported a funnel cloud.
Trained spotter reported golf ball sized hail.
Trained spotter reported half dollar sized hail.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2017Every state in 2017This day in weather historyThe tornado archive for Iowa, 2017Warnings in Iowa, June 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: 706362, 708341, 706364, 706365, 706366, 706367, 709535, 709537, 706368, 708348, 709538, 709539, 706369, 706370, 706371, 709541, 708342, 709542, 706373, 706372, 706374, 707250, 706375, 706376, 706378, 706377, 708346, 706379, 706380, 707251, 706381, 706382, 706383, 706384, 706385, 708339, 706386, 706387, 709543, 709545, and more.