Low pressure over Kansas moved northeast during the afternoon of the 11th into the morning of the 12th.  By dawn on the 12th, the low was over northeast Kansas.  A cold frontal boundary extended northeast from the low into northwest Iowa.  The atmosphere became unstable and was strongly sheared.  CAPE had increased to around 3000 J/kg by the late afternoon.  Downdraft CAPE was in the 800 to 1200 J/kg range with available CAPE in the -10 to -30 C layer of the atmosphere around 600 J/kg.  The lifted index was between -6 and -9 C.  The freezing level had risen to around 14,000 feet.  Deep moisture was drawn into the state on a 40 kt low level jet.  Precipitable water values were in the 1.3 to 1.5 inch range.  The LCL was quite low around 750 meters  The atmosphere was strongly sheared with 55 to 65 kts of effective shear available.  Thunderstorms formed along the cold front with initial development to the southwest of Iowa.  The storms developed northeast into Iowa and became severe.  There were numerous reports of high winds near 70 MPH, along with quarter to ping pong ball sized hail.  Several funnel cloud reports were received as well.  Flash flooding became a problem in Cass County near Atlantic.  A NWS survey team found that 4 tornadoes touched down in Guthrie, Dallas and Boone Counties.  One tornado formed south of Guthrie Center and tracked just over 10 miles northeastward and dissipated northeast of Lake Panorama where high end EF-1 and low EF-2 damage was found.  The average path width was 240 yards with maximum wind speed of 115 MPH.  A second tornado was an EF-1 tornado that formed on the west side of Lake Panorama and tracked east northeast to just south of Yale before dissipating.  The third tornado was just north of Dallas Center in Dallas County and ended about 5 miles northwest of Granger just before reaching HWY 141.  It was an EF-0 tornado with winds of 85 MPH. The fourth tornado was also an EF-0 occurring in Boone County where it touched down to the southeast of Luther.

Flash Flood in CASS, IOWA
From 11-MAY-14 20:26:00 to 12-MAY-14 02:30:00 (CST-6)
Location: ATLANTIC ARPT
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Highway 6 just northwest of Atlantic has water flowing up to curb level. Bull Creek drainage area was beginning to overflow.  Considerable street flooding in the town of Atlantic.

Hail in PALO ALTO, IOWA
From 11-MAY-14 18:52:00 to 11-MAY-14 18:52:00 (CST-6)
Location: CYLINDER
Magnitude: 1.25 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy Rain in CALHOUN, IOWA
From 11-MAY-14 19:05:00 to 11-MAY-14 20:05:00 (CST-6)
Location: JOLLEY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Rainfall of 1.98 inches in the past hour.

Hail in GREENE, IOWA
From 11-MAY-14 21:20:00 to 11-MAY-14 21:20:00 (CST-6)
Location: JEFFERSON MUNI ARPT
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Thunderstorm Wind in GUTHRIE, IOWA
From 11-MAY-14 21:03:00 to 11-MAY-14 21:03:00 (CST-6)
Location: JAMAICA
Magnitude: 61.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: NWS Employee

A large tree was snapped.

Hail in POLK, IOWA
From 11-MAY-14 21:40:00 to 11-MAY-14 21:40:00 (CST-6)
Location: URBANDALE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Thunderstorm Wind in DALLAS, IOWA
From 11-MAY-14 21:28:00 to 11-MAY-14 21:28:00 (CST-6)
Location: MINBURN
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Power lines and 8 to 10 inch diameter limbs down.

Thunderstorm Wind in GUTHRIE, IOWA
From 11-MAY-14 21:08:00 to 11-MAY-14 21:08:00 (CST-6)
Location: HERNDON
Magnitude: 56.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large branches snapped off of healthy tree.

Thunderstorm Wind in STORY, IOWA
From 11-MAY-14 21:50:00 to 11-MAY-14 21:50:00 (CST-6)
Location: ONTARIO
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Large tree limbs down.

Thunderstorm Wind in STORY, IOWA
From 11-MAY-14 21:51:00 to 11-MAY-14 21:51:00 (CST-6)
Location: ONTARIO
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Two to four inch limbs down at Lee Park.

Hail in CLARKE, IOWA
From 12-MAY-14 00:18:00 to 12-MAY-14 00:18:00 (CST-6)
Location: OSCEOLA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Thunderstorm Wind in CASS, IOWA
From 11-MAY-14 19:58:00 to 11-MAY-14 19:58:00 (CST-6)
Location: MARNE
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds estimated at 60 MPH.

Thunderstorm Wind in DALLAS, IOWA
From 11-MAY-14 21:22:00 to 11-MAY-14 21:22:00 (CST-6)
Location: DALLAS CENTER
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds estimated at 60 MPH at Highway 44 and R16.

Thunderstorm Wind in DALLAS, IOWA
From 11-MAY-14 21:26:00 to 11-MAY-14 21:26:00 (CST-6)
Location: ORTONVILLE
Magnitude: 52.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Minor tree damage reported.

Thunderstorm Wind in POLK, IOWA
From 11-MAY-14 21:50:00 to 11-MAY-14 21:50:00 (CST-6)
Location: FARRAR
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Social Media

Winds were estimated at 60 MPH.

Thunderstorm Wind in POLK, IOWA
From 11-MAY-14 21:53:00 to 11-MAY-14 21:53:00 (CST-6)
Location: LOVINGTON
Magnitude: 61.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Measured at 42nd and Douglas Ave.

Thunderstorm Wind in JASPER, IOWA
From 11-MAY-14 22:12:00 to 11-MAY-14 22:12:00 (CST-6)
Location: PRAIRIE CITY
Magnitude: 54.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in POLK, IOWA
From 11-MAY-14 21:40:00 to 11-MAY-14 21:40:00 (CST-6)
Location: URBANDALE
Magnitude: 56.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Wind gusts estimated at 60 to 70 MPH.

Heavy Rain in CASS, IOWA
From 11-MAY-14 07:15:00 to 12-MAY-14 07:15:00 (CST-6)
Location: GRISWOLD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter measured 4.10 inches of rain.  Most of the rain fell in a 2 to three hour period.

Tornado in GUTHRIE, IOWA
From 11-MAY-14 20:43:00 to 11-MAY-14 20:58:00 (CST-6)
Location: MONTEITH
Tornado F-scale: EF2
Property damage: 1.30M
Crop damage: 0.00K
Reported by: NWS Storm Survey

An NWS storm survey determined that an EF-2 tornado touched south southwest of Guthrie Center and tracked northeast across Lake Panorama and dissipating shortly thereafter.

Thunderstorm Wind in STORY, IOWA
From 11-MAY-14 21:50:00 to 11-MAY-14 21:50:00 (CST-6)
Location: ONTARIO
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Public

Trees down along Franklin Ave on the west side of Ames.

Thunderstorm Wind in ADAMS, IOWA
From 11-MAY-14 23:19:00 to 11-MAY-14 23:19:00 (CST-6)
Location: MERCER
Magnitude: 65.00 EG
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Public

Barn blown down by high winds.

Tornado in GUTHRIE, IOWA
From 11-MAY-14 20:56:00 to 11-MAY-14 21:03:00 (CST-6)
Location: FANSLERS
Tornado F-scale: EF1
Property damage: 400.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

EF-1 tornado started near Sunset Beach on Lake Panorama before heading northeast to just south of Yale.

Tornado in DALLAS, IOWA
From 11-MAY-14 21:21:00 to 11-MAY-14 21:27:00 (CST-6)
Location: MINBURN
Tornado F-scale: EF0
Property damage: 100.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

EF0 Tornado north of Dallas Center stayed in rural area and produced minor damage.

Thunderstorm Wind in WARREN, IOWA
From 12-MAY-14 05:05:00 to 12-MAY-14 05:05:00 (CST-6)
Location: NEW VIRGINIA
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A few shingles were removed from a new roof.  There was large tree limb damage in town and power lines down east of town. A metal panel was blown off a shed.

Tornado in BOONE, IOWA
From 11-MAY-14 21:44:00 to 11-MAY-14 21:46:00 (CST-6)
Location: NAPIER
Tornado F-scale: EF0
Property damage: 25.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Short-lived tornado that did some minor damage at a farmstead in rural Boone County before moving into open farmland.

Thunderstorm Wind in POLK, IOWA
From 11-MAY-14 21:30:00 to 11-MAY-14 21:30:00 (CST-6)
Location: CLIVE
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A large tree about one foot in diameter was uprooted.

Thunderstorm Wind in DALLAS, IOWA
From 11-MAY-14 21:21:00 to 11-MAY-14 21:21:00 (CST-6)
Location: DALLAS CENTER ARPT
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds estimated at 60 MPH at Highway 44 and 169 west of Dallas Center.

Thunderstorm Wind in POLK, IOWA
From 11-MAY-14 21:54:00 to 11-MAY-14 21:54:00 (CST-6)
Location: LOVINGTON
Magnitude: 65.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Very large two to three foot diameter tree down on a car.

Thunderstorm Wind in CALHOUN, IOWA
From 11-MAY-14 20:58:00 to 11-MAY-14 20:58:00 (CST-6)
Location: POMEROY
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large tree limb down, chair blown off the deck and a power transformer blown.

Thunderstorm Wind in SAC, IOWA
From 11-MAY-14 20:35:00 to 11-MAY-14 20:35:00 (CST-6)
Location: SAC CITY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large tree limbs down and table and chairs blown around on the deck.