During the day on the 15th, much of Iowa found itself firmly in the warm sector with a warm front/stationary front eventually settling across northern Iowa. Temperatures reached the upper 80s along with dew points in the mid to upper 60s, helping fuel MUCAPE values in excess of 2000 J/kg.
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.
During the day on the 15th, much of Iowa found itself firmly in the warm sector with a warm front/stationary front eventually settling across northern Iowa. Temperatures reached the upper 80s along with dew points in the mid to upper 60s, helping fuel MUCAPE values in excess of 2000 J/kg. Effective bulk shear was generally marginally supportive to supportive in the 25-45 kt range. Isolated storms initiated during the afternoon, eventually leading way to strong more widespread storms in the evening hours that resulted in primarily severe hail. In addition to the severe hail, a handful of thunderstorm damage, severe wind gusts, and even localized flash flooding were reported.
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 15, 11:43 AM CST, 24 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 1243 PM CDT Mon May 15 2017 .UPDATE... Issued at 1124 AM CDT Mon May 15 2017 Made some adjustments of afternoon highs northwest...though may need to lower further and farther south this afternoon. Convective complex still holding together but as of yet not appreciably organized. Expecting instability to increase along the warm frontal boundary...and as south/southwest outflow enhances temperature gradient this afternoon ...should see convection begin to ramp up again. Depending on timing...more favored areas may end up generally east of I35...though for now will not discount some stronger convection west of that line. Temperatures over the south should continue to reach the mid to upper 80s as some clouds are now filling in across the region due to heating and greater instability. /rev && .SHORT TERM.../Today through Tonight/ Issued at 420 AM CDT Mon May 15 2017 Shortwave over southwest South Dakota and northwest Nebraska will continue to ride the upper level ridge and move into Iowa later this morning. Currently projection reaches the far western forecast area b/t 13-15z and then across the rest of the CWA b/t 16z to 22z. Storms will mainly be north of Highway 30 to the Minnesota border but have chances going for a few hours south to include the DSM Metro around midday into the early afternoon. This first shortwave should quickly move east and allow for instability to build into the northern portions of the state, which will be the focus for severe weather potential tonight. Further south, strong capping inversion remains intact today into tonight and have low confidence with any storms making it through the cap and thus kept the forecast dry. The warm front is expected to to drape across southern Minnesota and possibly as far south into northern Iowa but certainly will be the focus for redevelopment and severe weather potential later tonight into Tuesday morning as the LLJ increasing. Surface dew points increase throughout the day and by this evening are likely to be in the middle to upper 60s across northern Iowa. Even if the surface CAPE increases to 1500 to 2000 J/kg along and south of the front, providing a decent gradient in far northern Iowa. Plus, steep mid- level lapse rates of 7.5-8 C/km should aid in the instability. LCL heights range around 500-1000m by around 06z Tuesday and good low level (0-0.5km and 0-1km) helicity in northern Iowa by this time. Deep layer shear is adequate for convection sustainability with low level shear (0-1km and 0-3km) range from 25-35 knots and 30-45 knots respectively providing a tornado threat, especially near the boundary. The main question is where the boundary ends up stalling out, northern Iowa or well into southern Minnesota. The odds are leaning towards southern Minnesota with decent cyclonic flow into the state to push it north. .LONG TERM.../Tuesday through Sunday/ Issued at 420 AM CDT Mon May 15 2017 Longer term generally dominated by mean trof in the western United States and southwest flow aloft over the Midwest including Iowa. The forecast area will be well within the warm sector on Tuesday with temperatures once again from 85 to 90 degrees in most locations. Soundings indicate a relatively strong cap in place which should limit any convection during the day. Surface front approaches western Iowa by late in the day with strong low level flow proceeding this front. Showers and thunderstorms are expected to develop and spread across western and northern Iowa on Tuesday night with some severe weather threat given the good instability and relatively strong shear. In addition, some localized heavy rainfall remains possible given the relatively high PWATS. Wednesday continues to be problematic in terms of severe weather potential as shortwave approaches the state. Wind fields will be strong although somewhat unidirectional with strong south to southwest flow. Ongoing convection will likely limit instability in western Iowa, however this become less of a concern farther east. There still appears to be a decent threat of severe convection in central and eastern portions of the forecast area, especially if convection remains limited through midday. All modes still appear possible at this point but will continue to monitor for additional clues to extent of any severe weather. Heavy rainfall will continue to be possible in the northwest third of the forecast area with a deformation area developing by afternoon on what should already be saturated soil from previous convection. There will be a break in activity on Thursday prior to the arrival of the next system. Current indications are that the bulk of instability may remain just south of Iowa along with the threat of severe weather. However, strong lift across the state along with ample moisture flowing northward may lead to moderate to heavy rainfall into central Iowa. This will have to be monitored closely, especially if the initial system produces heavy rainfall in the forecast area. It appears that the prolonged period of showers and a few storms will eventually end by Sunday as the axis of the western trof swings through the Midwest. Temperatures will also be much cooler into the weekend with the clouds and pcpn. && .AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/ Issued at 1243 PM CDT Mon May 15 2017 Concerns this period include ongoing convection...potential redevelopment tonight and to a lesser extent clouds and winds. Current cluster of storms over central Iowa is moving east along the warm front and beginning to show greater organization...expect trend to continue through 23z prior to exiting the area to the east. Potential for some svr storms...though may pass between TAF sites. KALO and KMCW still have a chance for some storms as areal coverage increases somewhat over the north...though confidence remains limited. Have included VCTS for now. Convection should bypass the far south sites KDSM/KOTM and with only small chances left at KFOD for now. Convection may redevelop aft 06z west/northeast of area...but will need to monitor. /rev && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && UPDATE...REV SHORT TERM...Podrazik LONG TERM...Cogil AVIATION...REV
Hazardous Weather Outlook National Weather Service Des Moines IA 932 AM CDT Mon May 15 2017 IAZ004>007-015>017-023>028-033>039-046>050-161445- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Greene-Boone-Story- Marshall-Tama- 932 AM CDT Mon May 15 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms are expected this morning through early evening developing over northwest Iowa then moving east southeast through mainly over western portions of the outlook area the afternoon and evening hours. There is an enhanced risk of severe storms north of Highway 20 from Kossuth County eastward. There is a slight risk of severe storms generally north of Highway 30. These storms may be capable of producing large hail, damaging winds and an isolated tornado. Brief heavy rainfall will also be possible through this evening. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday The threat for storms will return Tuesday night into Wednesday night. A few severe storms will be possible on Tuesday night with large hail and damaging winds mainly over the northwest half of the outlook area. Additional thunderstorms are expected on Wednesday into Wednesday evening, however the threat for severe weather has not been determined. Heavy rainfall will remain possible during this time which may lead to significant river rises or even some localized flash flooding. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon into this evening and again Tuesday night. IAZ044-045-057>062-070>075-081>086-092>097-161445- Crawford-Carroll-Audubon-Guthrie-Dallas-Polk-Jasper-Poweshiek- Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas- Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis- 932 AM CDT Mon May 15 2017 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Scattered thunderstorms are expected later today into tonight. These storms may be capable of producing large hail, damaging winds and an isolated tornado. Localized heavy rain will also be possible through tonight. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday The threat for storms will return Tuesday night into Wednesday night. A few severe storms will be possible on Tuesday night with large hail and damaging winds. Additional thunderstorms are expected on Wednesday into Wednesday evening, however the threat for severe weather has not been determined. Heavy rainfall will remain possible during this time which may lead to significant river rises or even some localized flash flooding. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon into this evening and again Tuesday night. REV
Special Weather Statement
National Weather Service Des Moines IA
1219 PM CDT MON MAY 15 2017
IAZ035-036-046-047-151815-
Hamilton IA-Boone IA-Greene IA-Webster IA-
1219 PM CDT MON MAY 15 2017
...STRONG STORMS MOVING THROUGH GREENE COUNTY...
At 1216 PM CDT, Doppler radar was tracking a strong thunderstorm 8
miles north of Jefferson, moving northeast at 35 mph.
Dime size hail and winds in excess of 30 mph will be possible with
this storm.
Locations impacted include...
Webster City, Gowrie, Dayton, Stratford, Stanhope, Lehigh, Duncombe,
Churdan, Harcourt, Paton, Kamrar, Boxholm, Woolstock, Dana, Woodman
Hollow State Park, Dolliver Memorial State Park, Webster City
Municipal Airport and Brushy Creek St Recreation Area.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional
information and possible warnings from the National Weather Service.
To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Des Moines.
&&
LAT...LON 4221 9445 4221 9440 4224 9440 4256 9391
4256 9382 4236 9357 4202 9446 4215 9454
TIME...MOT...LOC 1716Z 236DEG 40KT 4214 9441
BoksaThe Des Moines radar (KDMX), 63 km away, was scanning. The volume nearest the first event began at 18:07 UTC.
33 hail, 14 thunderstorm wind, 2 flash flood, 1 lightning, 1 heavy rain. Local standard time, as filed.
Trained spotter reported half dollar sized hail. Similar hail reported near Harcourt as well. This is a delayed report, time estimated by radar.
Trained spotter reported nickel sized hail.
Coop observer reported up to ping pong ball sized hail covering the ground in west Jewell. Time estimated by radar.
Public reported quarter sized hail.
Storm chaser reported penny sized hail.
Trained spotter reported 60 mph wind gusts along with penny sized hail and small tree branches down. This is a delayed report and time estimated by radar.
A power pole was reported down.
Public reported quarter sized hail via social media. This is a delayed report.
Trained spotter reported golf ball sized hail, and that it has been hailing for the past 5-10 minutes.
Trained spotter reported quarter sized hail. Time estimated via radar.
Trained spotter reported quarter sized hail 6 miles east of Humboldt along Highway 3.
Public reported just smaller than baseball sized hail. This is a delayed report, and from social media. Many car windows broken at a school event.
The fire is was caused by a lightning strike to the home that energized a telephone line and spread to roofing materials and insulation. Smoke was initially reported in the attic and flames on the roof line.
Trained spotter reported hail just under baseball in size. Time estimated by radar and report included a picture of the hail alongside a ruler.
Trained spotter reported golf ball sized hail.
Trained spotter reported quarter sized hail.
Public reported golf ball sized hail.
Emergency manager reported 4 to 5 inch diameter trees blown half way to the ground.
Trained spotter reported a number of large tree limbs down and at least one power line down. Most of the damage seemed to be confined to the west side of town. Time estimated by radar.
Media relayed report of six inch trees downed in town. Report came via social media and is a delayed report.
Trained spotter reported heavy rainfall of 1.6 inches along with hail around dime size or smaller.
Trained spotter reported nickel sized hail at the Iowa Specialty Hospital. Power reported out at the time as well.
Public reported to our Facebook page quarter sized hail. This is a delayed report and time estimated by radar.
Emergency manager reported quarter sized hail.
Major tree damage reported in the area with large limbs down.
Trained spotter reported half dollar sized hail. This is a delayed report.
Storm chaser reported 2 feet of fast rushing water has completely washed out Indigo Ave 1 mile south of Cerro Gordo County road B60 in Pleasant Valley Township along the upper reaches of the West Ford Cedar River. Water is moving swiftly and white capping over the roadway. Rain and small hail ongoing at the time of the report as well.
The Plainfield IDOT RWIS along Highway 218 recorded a 59 mph wind gust.
Trained spotter estimated 60-70 mph wind gusts, along with 4-6 inch diameter tree branches broken off.
Public reported golf ball sized hail via social media.
The Plainfield IDOT RWIS along Highway 218 recorded a 68 mph wind gust.
Public reported traffic poles downed and roof damage. Reported via social media.
Public reported half dollar sized hail along with tree limbs up to 6 inches in diameter broken off.
Public reported 6 inch tree branches down and some dime to quarter sized hail, and was getting bigger at the time.
Public reported some hail slightly larger than quarters.
KWWL shared a public image of a downed tree in Tripoli due to strong winds. Time estimated via radar.
KLMJ/KQCR-FM radio in Hampton reported quarter sized hail.
Public reported and shared a picture of ping pong ball sized hail onto our Facebook page. This is a delayed report and time is estimated by radar. Report from social media.
Quarter sized hail was reported and picture on KWWL's Facebook page. This is a delayed report and time estimated from radar.
Trained spotter reported that Vail Ave was washed out just south of 140th st.
Broadcast media reported that a two foot diameter tree was snapped.
Emergency manager reported downed limbs, at least two taking down power lines, unhealthy trees blown over, and power outage of about 30 minutes. This is a delayed report.
Law enforcement/dispatch relayed reports of half dollar sized hail SE of Lakota at the intersection of 220th Ave and 390th St.
Buffalo Center fire department reported quarter size hail. Time estimated from radar.
Buffalo Center fire department reported quarter sized hail. Time estimated from radar.
Mainly quarter sized hail with a few as large as golf balls.
Buffalo Center fire department reported ping pong ball sized hail. 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, 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: 693129, 698030, 693130, 693131, 693132, 693133, 698036, 693134, 698031, 693135, 698032, 693138, 693136, 693137, 693139, 695962, 693140, 693141, 693142, 693143, 693144, 693145, 693146, 693164, 693147, 693148, 693149, 698035, 693150, 693151, 693152, 693153, 693154, 693155, 693156, 693161, 693157, 693158, 693159, 693160, and more.