A warm front lifted north across the region during the afternoon and evening hours of May 29th followed by a weak cool front passage later that night.  As the warm front passed, temperatures warmed into the lower to mid 80s and dewpoint temperatures climbed into the 65 to 70 degree range.  The whole system was aided by an intense upper level low pressure area that moved from the eastern Rockies into the northern plains.  The combination of the high instability in place, the 2 fronts and the upper level disturbance created conditions that were favorable not only for severe thunderstorms, a few of which were supercells that produced tornadoes, but also areas of very heavy rainfall.  The heavy rain caused river flooding across southwest Iowa that in some cases lasted into early June.

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 19:25:00 to 29-MAY-08 19:25:00 (CST-6)
Location: DUNLAP
Magnitude: 61.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds which were estimated at 70 mph by a trained spotter flipped a fuel tank over and knocked down medium size tree limbs.

Thunderstorm Wind in SHELBY, IOWA
From 29-MAY-08 19:44:00 to 29-MAY-08 19:44:00 (CST-6)
Location: EARLING
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 21:30:00 to 29-MAY-08 21:30:00 (CST-6)
Location: RIVER SIOUX
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A Cooperative Observer estimated thunderstorm wind gusts of 65 mph with this storm.  This was the second severe thunderstorm to hit the area in a several hour period.

Flood in FREMONT, IOWA
From 30-MAY-08 16:00:00 to 31-MAY-08 23:59:00 (CST-6)
Location: BARTLETT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy rainfall during the evening of May 29th culminated nearly a week of scattered heavy rain producing thunderstorms that occurred along the Missouri River basin.  The heavy rains caused the Missouri River to flood from near its confluence with the Platte River near Plattsmouth, Nebraska, downstream through Rulo, Nebraska, which is in extreme southeast Richardson county.  Although those sites are in Nebraska the flooding affected the Iowa side of the river as well. Flooding along the Missouri River in Fremont county from this event began during the late afternoon hours of May 30th.  The river at Nebraska City crested just over 21 feet at 1115am CDT on June 1, flood stage is 18 feet.  The flooding continued into the evening hours of June 2nd.  The flooding affected mainly agricultural lowlands but also flooded a few county roads in the area, especially near the confluence with the Nishnabotna River near Hamburg which was also running high.

Flood in HARRISON, IOWA
From 30-MAY-08 06:00:00 to 30-MAY-08 09:15:00 (CST-6)
Location: MISSOURI VLY ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy rainfall during the evening and overnight hours of May 29th and 30th caused the Boyer River to briefly flood from around Logan to near Missouri Valley during the morning hours of May 30th.  The river reached a 19.9 foot crest at Logan around 830am CDT on May 30th, flood stage is 19 feet.  The flooding affected mainly just agricultural lowlands.

Hail in MONONA, IOWA
From 29-MAY-08 17:45:00 to 29-MAY-08 17:45:00 (CST-6)
Location: WHITING
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Tornado in MONONA, IOWA
From 29-MAY-08 19:00:00 to 29-MAY-08 19:10:00 (CST-6)
Location: MOORHEAD
Tornado F-scale: EF1
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

This tornado initially touched down in a grove of trees in a rural area southwest of Moorhead.  As it tracked east it hit a farmstead causing house and outbuilding damage and also severely damaged a grove of walnut trees.  Before the tornado lifted, it damaged two other separate groves of cottonwood trees and snapped a 3 foot diameter oak tree at its base and damaged a chicken coop at another farmstead.  The path width of the tornado damage was generally less than 100 yards, although it reached a maximum width of around 200 yards.

Flood in FREMONT, IOWA
From 30-MAY-08 22:15:00 to 31-MAY-08 15:30:00 (CST-6)
Location: HAMBURG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy rainfall during the evening and overnight hours of May 29th and 30th culminated nearly a week of scattered heavy rain producing thunderstorms that occurred over the Nishnabotna River basin.  The heavy rains caused the Nishnabotna River to surpass flood stage in the Hamburg area.  The river at Hamburg reached a 23.6 foot crest around 7am CDT on May 31st, flood stage is 23 feet.  The flooding affected mainly just some agricultural lowlands near town.

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 19:10:00 to 29-MAY-08 19:10:00 (CST-6)
Location: RIVER SIOUX
Magnitude: 55.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A Coop Observer estimated thunderstorm wind gusts of 60 to 65 mph downed 4 to 6 inch in diameter tree limbs.

Thunderstorm Wind in SHELBY, IOWA
From 29-MAY-08 22:15:00 to 29-MAY-08 22:15:00 (CST-6)
Location: HARLAN
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm wind gusts estimated at 60 mph blew a large tree onto a home.

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 19:15:00 to 29-MAY-08 19:15:00 (CST-6)
Location: MAGNOLIA
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

A report of 60 mph winds was received via amateur radio, although no local damage was noted at the time.

Flood in MILLS, IOWA
From 30-MAY-08 14:15:00 to 31-MAY-08 23:59:00 (CST-6)
Location: PACIFIC CITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Heavy rainfall during the evening of May 29th culminated nearly a week of scattered heavy rain producing thunderstorms that occurred along the Missouri River basin.  The heavy rains caused the Missouri River to flood from near its confluence with the Platte River near Plattsmouth, Nebraska, downstream through Rulo, Nebraska, which is in extreme southeast Richardson county.  Although those sites are in Nebraska the flooding affected the Iowa side of the river also. The river stage at Plattsmouth reached a 30 foot crest around 10am CDT on May 31st, flood stage is 26 feet.  This flooding event lasted into the early morning hours of June 2nd.  The flooding affected mainly agricultural lowlands.

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 19:35:00 to 29-MAY-08 19:35:00 (CST-6)
Location: PISGAH
Magnitude: 55.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm winds estimated at over 60 mph knocked down several large tree limbs and partially tore a metal roof off of a building in town.

Thunderstorm Wind in HARRISON, IOWA
From 29-MAY-08 19:30:00 to 29-MAY-08 19:30:00 (CST-6)
Location: LITTLE SIOUX
Magnitude: 55.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds blew a semi over at mile marker 94 on Interstate 29.  Large tree branches and power lines were also downed in the area and a roof of a house sustained damage.

Flash Flood in MONONA, IOWA
From 29-MAY-08 19:38:00 to 29-MAY-08 21:38:00 (CST-6)
Location: ONAWA MUNI ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rainfall flooded streets in town prompting their closure.  Apparent damage was minimal.

Thunderstorm Wind in PAGE, IOWA
From 29-MAY-08 23:45:00 to 30-MAY-08 00:00:00 (CST-6)
Location: SHENANDOAH
Magnitude: 55.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm wind gusts estimated at 60 to 65 mph uprooted and damaged large trees which knocked down power lines and damaged a house in the area.

Thunderstorm Wind in FREMONT, IOWA
From 29-MAY-08 23:40:00 to 29-MAY-08 23:40:00 (CST-6)
Location: IMOGENE
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Power lines were downed by thunderstorm winds gusting to 60 mph.