A very intense storm system moved through the central Rockies into the Plains.  The upper low looked more like a late winter or spring system, completely closed over northwest Kansas by the evening of the 20th.  The atmosphere was very unstable by the late afternoon with lifted indices around -11 and CAPE in the 4000 to 5000 J/kg range.  Other parameters were quite high as well with downdraft CAPE of 900 to 1500 J/kg and CAPE in the -10 to -30 C layer of the atmosphere of 500 to 1000 J/kg.  Initially the atmosphere was capped with 700 mb temperatures of 11 to 14 C.  There was a decent amount of shear available with 45 kts present.  Precipitable water values were quite high, approaching 2 inches.  A 40 to 50 kt inflow jet was present as well.  The LCL level was quite low, between 600 and 1000 meters.  A strong line of thunderstorms formed into a quasi-linear convective system.  It advanced into Iowa and produced high winds and some hail as it lifted east-northeast.  The hail was relatively small, an inch or less in diameter, as the freezing level was well over 15,000 feet resulting in quite a bit of melting of the hail as it fell.  The strongest winds were in Humboldt east of Ottosen where 80 MPH winds caused considerable tree and power line damage.  High winds downed a 50 foot high 66 X 76 foot barn southeast of Armstrong in Emmet County.  Grass, debris, and corn was blown across the highway.  The line continued to move northeast.  A microburst took place in Black Hawk County, causing considerable damage to a farmstead northwest of La Porte City.  Small tornadoes were also reported in central Iowa. One tornado touched down in Kossuth County northeast of Ottosen.  It damaged a house with the walls blown in and out.  Part of the roof was blown off the house. A grain auger was launched into the attic of the house.  Grain bins and trees were blown into a convergent path north-northwest of the house.  There was no damage on the west side of the farmstead.  The tornado track was short with wind damage done on farms within a 2 mile radius.  A tornado also touched down in Tama County near Cluttier.  The damage was very localized with tree tops snapped off.  Some minor house damage occurred with the gutter blown off into a truck.  The roof was taken off of an outbuilding.  In the town of Cluttier, one half mile to the southwest, large tree limbs were blown down.  Debris and corn were directed to the north, consistent with a small tornadic circulation at the farm site with EF0 damage.

Thunderstorm Wind in CARROLL, IOWA
From 20-JUN-11 21:12:00 to 20-JUN-11 21:12:00 (CST-6)
Location: CARROLL
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Local law enforcement reports power lines and fencing blown down near the 1500 block of Highway 71 in Carroll.

Thunderstorm Wind in HUMBOLDT, IOWA
From 20-JUN-11 22:18:00 to 20-JUN-11 22:18:00 (CST-6)
Location: OTTOSEN
Magnitude: 69.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Power lines and trees blown down.  Winds estimated 80 MPH.  Pea size hail was also reported.

Thunderstorm Wind in KOSSUTH, IOWA
From 20-JUN-11 22:30:00 to 20-JUN-11 22:30:00 (CST-6)
Location: ST JOSEPH
Magnitude: 57.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Survey by EM found one third of a roof of a quonset storage building was torn off and landed north of the building.

Thunderstorm Wind in EMMET, IOWA
From 20-JUN-11 22:48:00 to 20-JUN-11 22:48:00 (CST-6)
Location: ARMSTRONG
Magnitude: 61.00 EG
Property damage: 100.00K
Crop damage: 10.00K
Reported by: Emergency Manager

A 66 foot by 76 foot barn, 50 feet high, was destroyed by high winds.  A grain bin was blown off its concrete pad.  Debris, grass, and corn was blown across the highway.

Thunderstorm Wind in BUTLER, IOWA
From 20-JUN-11 23:45:00 to 20-JUN-11 23:45:00 (CST-6)
Location: APLINGTON
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Trees down in town.

Thunderstorm Wind in BLACK HAWK, IOWA
From 21-JUN-11 00:30:00 to 21-JUN-11 00:30:00 (CST-6)
Location: LA PORTE CITY
Magnitude: 69.00 EG
Property damage: 75.00K
Crop damage: 3.00K
Reported by: Public

Aluminum machine shed was ripped off its foundation and blown anticyclonically north and east, destroying it.   Debris from the shed continued in an anticyclonic path and was blown southward and wrapped into a grove of trees 100 feet to the east of the original location of the shed.  Door from the machine shed was blown 15 feet into a neighboring corn field.  Cattle barn 120 feet to the west was shifted south by 15 feet.

Thunderstorm Wind in CRAWFORD, IOWA
From 20-JUN-11 20:10:00 to 20-JUN-11 20:10:00 (CST-6)
Location: RICKETTS
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reports winds gusts of at least 60 MPH with storm.

Thunderstorm Wind in CASS, IOWA
From 20-JUN-11 20:53:00 to 20-JUN-11 20:53:00 (CST-6)
Location: CUMBERLAND
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated 60 MPH winds with 3 to 6 inch diameter branches down.

Hail in CALHOUN, IOWA
From 20-JUN-11 21:33:00 to 20-JUN-11 21:33:00 (CST-6)
Location: LAKE CITY
Magnitude: 1.00 
Property damage: 1.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail along with extremely heavy rain.

Thunderstorm Wind in POCAHONTAS, IOWA
From 20-JUN-11 22:00:00 to 20-JUN-11 22:00:00 (CST-6)
Location: POCAHONTAS MUNI ARPT
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Nickel size hail reported as well.

Hail in BOONE, IOWA
From 20-JUN-11 22:20:00 to 20-JUN-11 22:20:00 (CST-6)
Location: OGDEN
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Law Enforcement

Hail in STORY, IOWA
From 20-JUN-11 23:08:00 to 20-JUN-11 23:08:00 (CST-6)
Location: COLO
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Law Enforcement

Funnel Cloud in HARDIN, IOWA
From 20-JUN-11 23:21:00 to 20-JUN-11 23:21:00 (CST-6)
Location: LAWN HILLS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm Wind in CERRO GORDO, IOWA
From 20-JUN-11 23:30:00 to 20-JUN-11 23:30:00 (CST-6)
Location: MASON CITY
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Public

Six and one half inch diameter branch down outside of radio station.

Thunderstorm Wind in ADAMS, IOWA
From 20-JUN-11 21:04:00 to 20-JUN-11 21:04:00 (CST-6)
Location: CORNING
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Multiple moderate sized tree limbs down in town.

Thunderstorm Wind in POCAHONTAS, IOWA
From 20-JUN-11 22:10:00 to 20-JUN-11 22:10:00 (CST-6)
Location: ROLFE
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several 6 inch tree limbs down in town.

Thunderstorm Wind in KOSSUTH, IOWA
From 20-JUN-11 22:30:00 to 20-JUN-11 22:30:00 (CST-6)
Location: ST JOSEPH
Magnitude: 65.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Surveyed by EM and found three fourths of a grove of trees were downed.  Shingle damage also occurred with debris strewn north.

Thunderstorm Wind in JASPER, IOWA
From 20-JUN-11 23:30:00 to 20-JUN-11 23:30:00 (CST-6)
Location: NEWTON MUNI ARPT
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Small trees 8 to 10 inches in diameter were snapped at the base.

Thunderstorm Wind in POWESHIEK, IOWA
From 21-JUN-11 00:10:00 to 21-JUN-11 00:10:00 (CST-6)
Location: BROOKLYN
Magnitude: 57.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Public

Many branches were downed.  A gazebo was blown apart and debris strewn along a southwest to northeast path for about 75 feet. Some debris embedded 4 to 6 inches into the ground.

Thunderstorm Wind in CASS, IOWA
From 20-JUN-11 20:45:00 to 20-JUN-11 20:45:00 (CST-6)
Location: ATLANTIC ARPT
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Tree toppled and a few branches broken from nearby trees.

Tornado in KOSSUTH, IOWA
From 20-JUN-11 22:22:00 to 20-JUN-11 22:24:00 (CST-6)
Location: ST JOSEPH
Tornado F-scale: EF1
Property damage: 200.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Surveyed by the EM.  A house had walls blown in and out, part of the roof was off the house.  A motor from a grain auger was launched into the attic of the house with grain bins and trees down.  A convergent debris path was present north-northwest of the house with no damage on the west side of the farmstead.  A short track tornadic damage path was present with an area of straight line wind damage at other farms within 2 miles.

Tornado in TAMA, IOWA
From 21-JUN-11 00:15:00 to 21-JUN-11 00:16:00 (CST-6)
Location: CLUTIER
Tornado F-scale: EF0
Property damage: 75.00K
Crop damage: 5.00K
Reported by: NWS Storm Survey

A farm site on Highway V18 had tree tops snapped off.  Minor damage occurred to the house with a gutter blown onto a truck.  The roof was off of an outbuilding.  The narrow damage path was very localized. In the town of Cluttier, one half mile to the southwest, large tree limbs were down.  Debris and corn was directed to the north, consistent with small tornadic circulation at the farm site with EF0 damage.

Thunderstorm Wind in BLACK HAWK, IOWA
From 21-JUN-11 00:25:00 to 21-JUN-11 00:25:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Newspaper

Numerous tree branches down.

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-11 22:15:00 to 20-JUN-11 22:15:00 (CST-6)
Location: OGDEN
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm winds broke several large branches in the city of Ogden.

Thunderstorm Wind in HARDIN, IOWA
From 20-JUN-11 23:30:00 to 20-JUN-11 23:30:00 (CST-6)
Location: ACKLEY
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 15.00K
Reported by: Newspaper

High winds blew down corn in a field.