A juicy air mass was in place across the region with highs into the mid 90s and dew points into the mid 60s to low 70s. Resulting SB and MUCAPE values were in the 3000 to 4000 J/kg values. Other supporting factors for sustained severe storms were relatively lacking with little effective helicity to speak of, let alone effective shear. DCAPE, however, was fairly robust in the 1400-1700 J/kg range.  Additionally, a weak north-south boundary was laid up across western Iowa that saw a brief landspout near Plover during initial development of storms. Overall, the majority of reports through central and northern Iowa were severe hail and winds from short-lived convection.

Hail in MARSHALL, IOWA
From 28-MAY-18 14:52:00 to 28-MAY-18 14:52:00 (CST-6)
Location: CLEMONS
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail and small branches down between Saint Anthony and Clemons.

Thunderstorm Wind in WARREN, IOWA
From 28-MAY-18 15:48:00 to 28-MAY-18 15:48:00 (CST-6)
Location: CLARKSON
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a large tree branch down.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:05:00 to 28-MAY-18 16:05:00 (CST-6)
Location: MESERVEY
Magnitude: 56.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a roof removed from a farm building near Meservey along with 4 inch diameter tree branches down.  Time was estimated from radar.

Thunderstorm Wind in HANCOCK, IOWA
From 28-MAY-18 16:07:00 to 28-MAY-18 16:07:00 (CST-6)
Location: GOODELL
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported 10 inch diameter tree branch, about 12 feet tall, down along with several smaller branches.

Thunderstorm Wind in FRANKLIN, IOWA
From 28-MAY-18 16:08:00 to 28-MAY-18 16:08:00 (CST-6)
Location: ALEXANDER
Magnitude: 52.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported portion of roof removed from a farm building. Time estimated from radar.

Thunderstorm Wind in HANCOCK, IOWA
From 28-MAY-18 16:22:00 to 28-MAY-18 16:22:00 (CST-6)
Location: GARNER
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a large healthy tree, about 2 feet in diameter, snapped at the base just east of Garner.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:25:00 to 28-MAY-18 16:25:00 (CST-6)
Location: VENTURA
Magnitude: 61.00 EG
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Public

Public reported multiple trees down, some 1 foot plus diameter, and telephone pole damage along Highway B35 southeast of Ventura.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:43:00 to 28-MAY-18 16:43:00 (CST-6)
Location: MASON CITY
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported widespread tree damage including branches up to 2 to 3 inches in diameter down.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:47:00 to 28-MAY-18 16:47:00 (CST-6)
Location: MASON CITY
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported numerous 3 to 4 inch diameter tree branches down throughout Mason City along with a few larger trees down as well.  Hail sized was unknown at the time.  Time was estimated from radar.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:49:00 to 28-MAY-18 16:49:00 (CST-6)
Location: CLEAR LAKE LAKE
Magnitude: 61.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported 6 inch diameter tree limbs and multiple power lines down throughout the town of Clear Lake.  Several boats on Clear Lake were either capsized or lost power.  Time was estimated by radar.

Hail in CERRO GORDO, IOWA
From 28-MAY-18 16:51:00 to 28-MAY-18 16:56:00 (CST-6)
Location: MASON CITY
Magnitude: 1.00 
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported hail for 5 minutes with up to quarter sized hail being driven by high winds and heavy rain.

Hail in STORY, IOWA
From 28-MAY-18 13:43:00 to 28-MAY-18 13:43:00 (CST-6)
Location: MAXWELL
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail falling on the south side of Maxwell along with strong winds. No wind damage was observed at the time.

Hail in STORY, IOWA
From 28-MAY-18 14:02:00 to 28-MAY-18 14:02:00 (CST-6)
Location: COLLINS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported quarter sized hail falling.

Hail in POLK, IOWA
From 28-MAY-18 15:49:00 to 28-MAY-18 15:49:00 (CST-6)
Location: AVON
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported quarter sized hail via the mPING application.

Thunderstorm Wind in WRIGHT, IOWA
From 28-MAY-18 15:50:00 to 28-MAY-18 15:50:00 (CST-6)
Location: CLARION ARPT
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

The Clarion Airport AWOS station recorded a 58 mph wind gust.

Thunderstorm Wind in POLK, IOWA
From 28-MAY-18 16:06:00 to 28-MAY-18 16:06:00 (CST-6)
Location: DES MOINES
Magnitude: 61.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a large tree snapped at the trunk near Davis and south Union. Time was estimated from radar.

Hail in HANCOCK, IOWA
From 28-MAY-18 16:10:00 to 28-MAY-18 16:10:00 (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.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:30:00 to 28-MAY-18 16:30:00 (CST-6)
Location: CLEAR LAKE
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported several tree branches, power lines, and a few tree trunks down through the town of Clear Lake.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:30:00 to 28-MAY-18 16:30:00 (CST-6)
Location: BURCHINAL
Magnitude: 53.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Iowa DOT mesonet station along Interstate 35 recorded a 61 mph wind gust.

Thunderstorm Wind in HANCOCK, IOWA
From 28-MAY-18 16:31:00 to 28-MAY-18 16:31:00 (CST-6)
Location: GARNER
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported 2 inch tree limbs down and debris blowing across the road.  There was also up to nickel sized hail.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:36:00 to 28-MAY-18 16:36:00 (CST-6)
Location: CLEAR LAKE
Magnitude: 61.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported 60 plus MPH wind gusts, large trees down, and power lines down.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:36:00 to 28-MAY-18 16:36:00 (CST-6)
Location: (MCW)MASON CITY MUNI
Magnitude: 55.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Mason City Municipal Airport ASOS station recorded a 63 mph wind gust.

Thunderstorm Wind in CERRO GORDO, IOWA
From 28-MAY-18 16:38:00 to 28-MAY-18 16:38:00 (CST-6)
Location: (MCW)MASON CITY MUNI
Magnitude: 59.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Mason City Municipal Airport recorded a 68 mph wind gust.

Tornado in POCAHONTAS, IOWA
From 28-MAY-18 13:20:00 to 28-MAY-18 13:22:00 (CST-6)
Location: PLOVER
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.10K
Reported by: Trained Spotter

Landspout formed under developing thunderstorm in the early afternoon.  Photographed from a few different angles and persisted for a few minutes before dissipating.  Stayed in rural areas between Rolfe and Plover in open agricultural fields.  Did no damage other than to emergent crops.