A stationary front was draped across much of northwest and northern Iowa, acting as a focal point for convection during the overnight and daytime hours. By mid-morning mixed layer CAPE values were already approaching and exceeding 2000 J/kg.
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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 stationary front was draped across much of northwest and northern Iowa, acting as a focal point for convection during the overnight and daytime hours. By mid-morning mixed layer CAPE values were already approaching and exceeding 2000 J/kg. The initial set of storms initiated in eastern Nebraska and progressed into Iowa. After initially weakening, said storms strengthened and became roughly linear. The resulting damage report was for damaging winds in northwest Iowa. Later that afternoon with the front remaining over northern Iowa, storms initiated in the warm sector, with the initial and strongest storm producing a pair of severe hail 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 Jun 12, 5:33 AM CST, 4 hours 54 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 633 AM CDT Mon Jun 12 2017 .SHORT TERM.../Today through Tonight/ Issued at 338 AM CDT Mon Jun 12 2017 Trough axis in place across the northwest to north central portions of the state, with an elongated area of surface low pressure stretching from southern Ontario southwestward into western Kansas. Have westerly flow aloft that will start to dip down to more southwesterly flow as a large upper trough digs into the intermountain west today. Sfc trough/weak cool front associated with the upper trough moving through the Hudson Bay region, with the front stalling out across the northern CWA and lifting back northward tonight as a warm front in response to the western upper trough digging eastward through the Rockies into early Tuesday. Some weak sfc convergence along the boundary, with a few weak echoes showing up on radar across southern MN the past few hours. This activity expected to stay quite isolated and weak before diminishing toward 12-14Z. Additional development then expected this afternoon in vicinity of the boundary, with continued redevelopment through the evening into the overnight hours. Strong southerly flow to develop today, with moisture advecting northward and pooling along the boundary should aid in storm development by mid/late afternoon across far northern IA/southern MN. Some severe potential this afternoon with any development near the frontal boundary with deep layer shear around 30kts and a large amount of CAPE expected. This would suggest mainly severe threats of damaging winds and large hail. Higher freezing level also so could see some brief heavy rain in areas beneath any strong storm that develops. As for temperatures today, still a warm air mass in place with also have some clouds so this will limit the mixing/overall warming some especially in areas near the frontal boundary across the north. Therefore have highs around the upper 80s in the far north, and the mid 90s across the central and south. Record highs mainly the mid to upper 90s across the CWA and likely should not see values that high today. However still expected to be within 3-4 degrees of record highs, so maintained the near record wording to highlight the warm temperatures given the string of warm days over the weekend into today. Should still see some breezy conditions, although overall winds should not be as gusty as in the past few days with gusts mainly in the 20-30 mph range today versus the 30-40 mph range the past few days. .LONG TERM.../Tuesday through Sunday/ Issued at 338 AM CDT Mon Jun 12 2017 The weather pattern for the remainder of this week will be more typical of mid to late summer than early June, characterized by persistent but nebulous thunderstorm chances, repeated possibilities of severe weather but with difficult to pin down details, wide discrepancies in model solutions, and a continuation of above normal temperatures. At the beginning of the period, on Tuesday, a large gyre will be located over the northern U.S. Rockies and will subsequently move northeast into south central Canada, then east toward Hudson Bay by the end of the week. As the low pressure center moves into Canada, from Tuesday through Wednesday, Iowa will reside with cyclonic, southwesterly flow aloft. A fairly robust shortwave will move through this flow over the Midwest late on Tuesday, but most of the energy associated with this feature will remain just northwest of our area. A second, much more subtle shortwave may move over the region on Wednesday. During the day on Tuesday our forecast area will reside firmly within the warm sector between our old friend, the warm front that has been vacillating across the upper Midwest for a few days already, and a surface trough to our west associated with the parent system and approaching shortwave. With moderate southerly low-level flow, warm morning start temperatures, and strong insolation, temperatures should have no problem rising toward the mid-90s on Tuesday afternoon, with heat index values in the lower 100s for a few hours. By the late afternoon and evening explosive convective development should occur along the aforementioned trough to our west, as the forcing associated with the shortwave intersects with the low-level boundary at peak diurnal heating time. This activity will carry an attendant severe weather risk, but it appears that it will develop well to our west, probably over central/eastern Nebraska, and move generally northeastward through the evening, possibly clipping our northwestern counties. After dark, with the parent system moving off to our north/northwest, the convection should bleed eastward across central Iowa carried by its own outflow momentum, but with a steadily decreasing severe weather threat as instability and shear diminish and the storms leave their favorable upper-level forcing environment. The surface trough to our west on Tuesday will finally traverse our forecast area late Wednesday and Wednesday night. As it moves through, there appears to be a good opportunity for additional convective development across about the southeast half of Iowa. Ahead of the trough instability will be high to extreme, and if the subtle impulse aloft mentioned earlier materializes and lines up with this time and space window, we could see very strong updrafts in an environment of modest but sufficient deep-layer shear to support severe weather. This threat will bear close watching over the next couple of days. As the surface trough moves off to our southeast on Wednesday night it will initially scour out any convection, however, it will be a week boundary and the airmass behind it will still be warm and unstable, with highs in the lower 90s on Thursday and Friday. It is in this time frame that longer range prognostic models have been struggling mightily, as the large early-week gyre moves across Canada and results in a zonal steering flow pattern over the Midwest. It is likely that subtle impulses moving through this flow will trigger thunderstorms at times late in the work week, but given the nebulous forcing and low-level flow, trying to refine timing and location details for any such development is folly at this time. This uncertainty will continue through the weekend, with lingering POPs carried through the extended forecast. && .AVIATION.../For the 12Z TAFS through 12Z Tuesday morning/ Issued at 633 AM CDT Mon Jun 12 2017 Some mid clouds around through the period, with a chance for thunderstorms along the MN/IA border by this afternoon into the evening hours. Have highlighted VCTS at KMCW for the period of greatest chance. Otherwise mainly southerly to southeasterly winds through the forecast period, and VFR conditions. Late tonight some chance for fog/low clouds with a boundary near KMCW and have highlighted with a 6sm BR as confidence is low to drop below VFR at this time. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...Beerends LONG TERM...Lee AVIATION...Beerends
Hazardous Weather Outlook National Weather Service Des Moines IA 428 AM CDT Mon Jun 12 2017 IAZ004>007-015>017-023>028-033>039-050-131100- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Tama- 428 AM CDT Mon Jun 12 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms will be possible at times today and tonight. There is a slight risk of severe weather, with large hail and damaging winds the primary threats. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday Heat is expected to build again into Tuesday. Highs will reach the lower to middle 90s during the afternoon with heat index values reaching or just exceeding 100 degrees at times. Intermittent thunderstorm chances are forecast from late Tuesday into Wednesday, then again from late Thursday through the weekend. Severe weather may be possible at times, especially late Tuesday and Wednesday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed late Tuesday. IAZ044>049-057>062-070>075-081>086-092>097-131100- Crawford-Carroll-Greene-Boone-Story-Marshall-Audubon-Guthrie- Dallas-Polk-Jasper-Poweshiek-Cass-Adair-Madison-Warren-Marion- Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold- Decatur-Wayne-Appanoose-Davis- 428 AM CDT Mon Jun 12 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Hot and humid weather will continue today, with heat index values approaching or just exceeding 100 degrees at times in the afternoon. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday The heat wave will continue on Tuesday, with high temperatures in the lower to middle 90s and heat index values exceeding 100 degrees at times. Intermittent thunderstorm chances are forecast from late Tuesday into Wednesday, then again from late Thursday through the weekend. Severe weather may be possible at times, especially late Tuesday and Wednesday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed late Tuesday. Lee
Special Weather Statement National Weather Service Des Moines IA 654 AM CDT Mon Jun 12 2017 IAZ038-039-048>050-057>062-070>075-081>086-092>097-121700- Grundy-Black Hawk-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- Including the cities of Grundy Center, Reinbeck, Conrad, Dike, Wellsburg, Waterloo, Cedar Falls, Ames, Marshalltown, Tama, Toledo, Traer, Dysart, Gladbrook, Audubon, Exira, Guthrie Center, Panora, Bayard, Casey, Perry, Waukee, Adel, Des Moines, Newton, Grinnell, Atlantic, Greenfield, Stuart, Adair, Fontanelle, Winterset, Earlham, Indianola, Norwalk, Carlisle, Pella, Knoxville, Oskaloosa, Corning, Creston, Osceola, Chariton, Albia, Ottumwa, Bedford, Lenox, New Market, Mount Ayr, Lamoni, Leon, Corydon, Seymour, Allerton, Humeston, Centerville, and Bloomfield 654 AM CDT Mon Jun 12 2017 ...Hot and Humid Conditions Expected Again Today... Near record high temperatures are expected again today, with highs topping out in the low to mid 90s. Dewpoints will hover around 70 degrees through the day. The heat and humidity will combine to make it feel much warmer as heat index values climb to around 100 degrees this afternoon. Several days of high heat and humidity without spending some time in air conditioning, can lead to heat-related illness. If spending time outdoors, please take frequent breaks and stay properly hydrated. MJB
The Sioux Falls radar (KFSD), 158 km away, was scanning. The volume nearest the first event began at 16:27 UTC.
2 hail, 1 thunderstorm wind. Local standard time, as filed.
Trained spotter reported heavy damage to corn and bean fields, likely from combination of hail and high winds. Power lines also down across the road and numerous tree branches down. This is a delayed report. Time radar estimated.
Trained spotter reported quarter size hail.
Trained spotter reported dime to quarter 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 historyWarnings 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: 705370, 705371, 705372.