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.

Flash Flood in HANCOCK, IOWA
From 15-MAY-17 18:30:00 to 15-MAY-17 23:00:00 (CST-6)
Location: GOODELL
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported that Vail Ave was washed out just south of 140th st.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 18:42:00 to 15-MAY-17 18:42:00 (CST-6)
Location: TRIPOLI
Magnitude: 61.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Broadcast media reported that a two foot diameter tree was snapped.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 18:43:00 to 15-MAY-17 18:43:00 (CST-6)
Location: TRIPOLI
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

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.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 17:20:00 to 15-MAY-17 17:20:00 (CST-6)
Location: PLAINFIELD
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The Plainfield IDOT RWIS along Highway 218 recorded a 59 mph wind gust.

Hail in WEBSTER, IOWA
From 15-MAY-17 12:07:00 to 15-MAY-17 12:07:00 (CST-6)
Location: DAYTON
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported half dollar sized hail.  Similar hail reported near Harcourt as well.  This is a delayed report, time estimated by radar.

Hail in CERRO GORDO, IOWA
From 15-MAY-17 17:04:00 to 15-MAY-17 17:04:00 (CST-6)
Location: DOUGHERTY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported to our Facebook page quarter sized hail.  This is a delayed report and time estimated by radar.

Hail in KOSSUTH, IOWA
From 15-MAY-17 22:15:00 to 15-MAY-17 22:15:00 (CST-6)
Location: STEVENS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Buffalo Center fire department reported quarter size hail.  Time estimated from radar.

Hail in HAMILTON, IOWA
From 15-MAY-17 12:30:00 to 15-MAY-17 12:30:00 (CST-6)
Location: STANHOPE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported nickel sized hail.

Hail in HAMILTON, IOWA
From 15-MAY-17 12:54:00 to 15-MAY-17 12:54:00 (CST-6)
Location: ELLSWORTH
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported quarter sized hail.

Hail in WORTH, IOWA
From 15-MAY-17 14:33:00 to 15-MAY-17 14:33:00 (CST-6)
Location: TENOLD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Storm chaser reported penny sized hail.

Thunderstorm Wind in HANCOCK, IOWA
From 15-MAY-17 15:51:00 to 15-MAY-17 15:51:00 (CST-6)
Location: DENHART
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

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.

Hail in HUMBOLDT, IOWA
From 15-MAY-17 16:01:00 to 15-MAY-17 16:01:00 (CST-6)
Location: GILMORE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported quarter sized hail via social media.  This is a delayed report.

Hail in WRIGHT, IOWA
From 15-MAY-17 16:38:00 to 15-MAY-17 16:38:00 (CST-6)
Location: EAGLE GROVE
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported golf ball sized hail.

Hail in CERRO GORDO, IOWA
From 15-MAY-17 16:44:00 to 15-MAY-17 16:44:00 (CST-6)
Location: THORNTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail.

Hail in WRIGHT, IOWA
From 15-MAY-17 16:48:00 to 15-MAY-17 16:48:00 (CST-6)
Location: GOLDFIELD
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported golf ball sized hail.

Thunderstorm Wind in FRANKLIN, IOWA
From 15-MAY-17 16:49:00 to 15-MAY-17 16:49:00 (CST-6)
Location: SHEFFIELD
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

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.

Thunderstorm Wind in FRANKLIN, IOWA
From 15-MAY-17 16:49:00 to 15-MAY-17 16:49:00 (CST-6)
Location: CHAPIN
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported 4 to 5 inch diameter trees blown half way to the ground.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:14:00 to 15-MAY-17 17:14:00 (CST-6)
Location: ALEXANDER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported quarter sized hail.

Hail in WRIGHT, IOWA
From 15-MAY-17 17:01:00 to 15-MAY-17 17:01:00 (CST-6)
Location: CLARION
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported nickel sized hail at the Iowa Specialty Hospital.  Power reported out at the time as well.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:16:00 to 15-MAY-17 17:16:00 (CST-6)
Location: ALEXANDER
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported half dollar sized hail.  This is a delayed report.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 17:28:00 to 15-MAY-17 17:28:00 (CST-6)
Location: PLAINFIELD
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter estimated 60-70 mph wind gusts, along with 4-6 inch diameter tree branches broken off.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 17:30:00 to 15-MAY-17 17:30:00 (CST-6)
Location: PLAINFIELD
Magnitude: 59.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

The Plainfield IDOT RWIS along Highway 218 recorded a 68 mph wind gust.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:30:00 to 15-MAY-17 17:30:00 (CST-6)
Location: LATIMER
Magnitude: 1.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported golf ball sized hail via social media.

Thunderstorm Wind in FRANKLIN, IOWA
From 15-MAY-17 17:40:00 to 15-MAY-17 17:40:00 (CST-6)
Location: HAMPTON
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported 6 inch tree branches down and some dime to quarter sized hail, and was getting bigger at the time.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:42:00 to 15-MAY-17 17:42:00 (CST-6)
Location: HAMPTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported some hail slightly larger than quarters.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:45:00 to 15-MAY-17 17:45:00 (CST-6)
Location: HAMPTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KLMJ/KQCR-FM radio in Hampton reported quarter sized hail.

Hail in BUTLER, IOWA
From 15-MAY-17 18:05:00 to 15-MAY-17 18:05:00 (CST-6)
Location: DUMONT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Quarter sized hail was reported and picture on KWWL's Facebook page.  This is a delayed report and time estimated from radar.

Heavy Rain in BUTLER, IOWA
From 15-MAY-17 17:00:00 to 15-MAY-17 18:30:00 (CST-6)
Location: GREENE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 1.6 inches along with hail around dime size or smaller.

Hail in KOSSUTH, IOWA
From 15-MAY-17 22:08:00 to 15-MAY-17 22:08:00 (CST-6)
Location: GERMAN VLY
Magnitude: 1.25 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement/dispatch relayed reports of half dollar sized hail SE of Lakota at the intersection of 220th Ave and 390th St.

Hail in WEBSTER, IOWA
From 15-MAY-17 12:10:00 to 15-MAY-17 12:10:00 (CST-6)
Location: DAYTON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Lightning in CERRO GORDO, IOWA
From 15-MAY-17 16:32:00 to 15-MAY-17 16:32:00 (CST-6)
Location: CLEAR LAKE
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Newspaper

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.

Thunderstorm Wind in HANCOCK, IOWA
From 15-MAY-17 16:00:00 to 15-MAY-17 16:00:00 (CST-6)
Location: BRITT
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A power pole was reported down.

Hail in CERRO GORDO, IOWA
From 15-MAY-17 16:15:00 to 15-MAY-17 16:15:00 (CST-6)
Location: CENTRAL HGTS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in WINNEBAGO, IOWA
From 15-MAY-17 22:59:00 to 15-MAY-17 22:59:00 (CST-6)
Location: RAKE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in FRANKLIN, IOWA
From 15-MAY-17 16:50:00 to 15-MAY-17 16:50:00 (CST-6)
Location: SHEFFIELD
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Media relayed report of six inch trees downed in town.  Report came via social media and is a delayed report.

Hail in WINNEBAGO, IOWA
From 15-MAY-17 22:15:00 to 15-MAY-17 22:15:00 (CST-6)
Location: BUFFALO CENTER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Buffalo Center fire department reported quarter sized hail.  Time estimated from radar.

Thunderstorm Wind in CERRO GORDO, IOWA
From 15-MAY-17 17:15:00 to 15-MAY-17 17:15:00 (CST-6)
Location: ROCKWELL
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Major tree damage reported in the area with large limbs down.

Hail in KOSSUTH, IOWA
From 15-MAY-17 15:30:00 to 15-MAY-17 15:30:00 (CST-6)
Location: WESLEY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in KOSSUTH, IOWA
From 15-MAY-17 22:45:00 to 15-MAY-17 22:45:00 (CST-6)
Location: BUFFALO CENTER
Magnitude: 1.75 
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Mainly quarter sized hail with a few as large as golf balls.

Hail in HAMILTON, IOWA
From 15-MAY-17 12:42:00 to 15-MAY-17 12:42:00 (CST-6)
Location: JEWELL
Magnitude: 1.50 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported up to ping pong ball sized hail covering the ground in west Jewell.  Time estimated by radar.

Hail in HANCOCK, IOWA
From 15-MAY-17 16:25:00 to 15-MAY-17 16:25:00 (CST-6)
Location: GOODELL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail.  Time estimated via radar.

Hail in HUMBOLDT, IOWA
From 15-MAY-17 16:28:00 to 15-MAY-17 16:28:00 (CST-6)
Location: THOR
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail 6 miles east of Humboldt along Highway 3.

Hail in HUMBOLDT, IOWA
From 15-MAY-17 16:23:00 to 15-MAY-17 16:28:00 (CST-6)
Location: RENWICK MUNI ARPT
Magnitude: 1.75 
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported golf ball sized hail, and that it has been hailing for the past 5-10 minutes.

Hail in HUMBOLDT, IOWA
From 15-MAY-17 16:30:00 to 15-MAY-17 16:30:00 (CST-6)
Location: THOR
Magnitude: 2.50 
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Social Media

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.

Flash Flood in CERRO GORDO, IOWA
From 15-MAY-17 17:17:00 to 15-MAY-17 23:00:00 (CST-6)
Location: SWALEDALE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

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.

Hail in WRIGHT, IOWA
From 15-MAY-17 16:37:00 to 15-MAY-17 16:37:00 (CST-6)
Location: GOLDFIELD
Magnitude: 2.50 
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported hail just under baseball in size.  Time estimated by radar and report included a picture of the hail alongside a ruler.

Thunderstorm Wind in BREMER, IOWA
From 15-MAY-17 17:44:00 to 15-MAY-17 17:44:00 (CST-6)
Location: TRIPOLI
Magnitude: 61.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KWWL shared a public image of a downed tree in Tripoli due to strong winds.  Time estimated via radar.

Thunderstorm Wind in FRANKLIN, IOWA
From 15-MAY-17 17:35:00 to 15-MAY-17 17:35:00 (CST-6)
Location: HAMPTON
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported traffic poles downed and roof damage.  Reported via social media.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:50:00 to 15-MAY-17 17:50:00 (CST-6)
Location: HANSELL
Magnitude: 1.50 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Social Media

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.

Hail in WINNEBAGO, IOWA
From 15-MAY-17 22:50:00 to 15-MAY-17 22:50:00 (CST-6)
Location: BUFFALO CENTER
Magnitude: 1.50 
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Buffalo Center fire department reported ping pong ball sized hail.  Time estimated from radar.

Hail in FRANKLIN, IOWA
From 15-MAY-17 17:38:00 to 15-MAY-17 17:38:00 (CST-6)
Location: HAMPTON
Magnitude: 1.25 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Public

Public reported half dollar sized hail along with tree limbs up to 6 inches in diameter broken off.