April 2011 Iowa–Wisconsin tornado outbreak

April 2011 Iowa-Wisconsin tornado outbreak

Damage from the Mapleton, Iowa tornado
Type	Tornado outbreak
Duration	April 9 – April 11, 2011
Tornadoes confirmed	43
Max rating1	EF4 tornado
Duration of tornado outbreak2	48 hours, 6 minutes
Damage	$2.2 billion
1Most severe tornado damage; see Enhanced Fujita scale 2Time from first tornado to last tornado

The April 2011 Iowa–Wisconsin tornado outbreak was one of several tornado outbreaks in the U.S. to take place during the record month of April 2011. Producing 43 tornadoes across five states, widespread damage took place; however, no fatalities resulted from the event due to timely warnings. In Wisconsin, 16 tornadoes touched down, ranking this outbreak as the state's largest April event on record as well as one of the largest single-day events during the course of any year. The strongest of these storms was an EF4 tornado that touched down south of Pocahontas, Iowa on April 9. Between 0256 and 0257 UTC (9:56 and 9:57 pm CDT) that day, five tornadoes were on the ground simultaneously in Pocahontas County, Iowa, all of which were from one supercell thunderstorm.

Throughout Iowa, damage from the storms is estimated at $78.6 million, much of which likely took place in and around Mapleton. In addition to the tornadoes, Texas experienced a widespread straight-line wind and hail event, leaving $100 million in damage. Overall, losses from the storm system reached $2.2 billion, making it the third of a record ten billion dollar disasters in 2011.

Meteorological synopsis

On April 9, a progressive upper-level trough moved east out of the Rocky Mountains and over the Midwest. Owing to early morning thunderstorms, moisture levels in the central Great Plains increased; however, capping in the region would limit daytime activity before atmospheric instability allowed for severe weather. forecast models indicated that the low-level jetstream would produce significant wind shear, aiding in the formation of possible tornadic supercell thunderstorms, and CAPE (convective available potential energy) values could exceed 3,000 j/kg. In light of this, the Storm Prediction Center (SPC) stated a moderate risk of severe weather for areas around the Minnesota-Iowa border. A slight risk was also defined for a broader region surrounding the moderate as well as a narrow line extending southward to Texas. A warm front began developing along the southeastern side of the low pressure area as it moved over The Dakotas.

File:April 9, 2011 Arthur, Iowa tornado.jpg

Picture of an EF2 tornado west of Arthur, Iowa on April 9.

During the evening hours of April 9, the SPC issued a tornado watch for western and northern Iowa, eastern Nebraska and southeast South Dakota. Conditions within this region were favorable for the development of multiple tornadic storms and there was a 70 percent chance of multiple touchdowns. Around 2250 UTC (5:50 pm CDT), a strong thunderstorm developed over Burt/Cuming Counties in northeastern Nebraska. This cell slowly tracked east-northeastward and developed into a supercell as it moved into Monona County, Iowa. By 0021 UTC (7:21 pm CDT), a small tornado touched down roughly 2 miles (3.2 km) southwest of Mapleton. Within minutes, this storm quickly grew and intensified as it moved closer to the city. The tornado passed directly over the city at low-end EF3 strength. Turning northward, the tornado dissipated about 1 mile (1.6 km) north of Mapleton. A separate EF2 tornado struck the town of Early, where considerable damage occurred to homes and businesses.

File:Arkdale Wisconsin April 10 2011 Tornado Damage 1 year later.jpg

Cottonville, Wisconsin EF2 tornado damage, one year later

Tracking northeastward, the supercell moved into Ida County, another tornado touched down around 0115 UTC (8:15 pm CDT) to the west of Arthur. This storm remained on the ground for 5 to 10 minutes, during which it damaged a few structures, before dissipating 2 miles (3.2 km) northwest of Arthur. Around 0120 UTC (8:20 pm CDT), the cell entered Sac County and the first in a series of multiple tornadoes touched down northwest of Odebolt. Over the following three hours, 13 tornadoes touched down across several counties. Around 0208 UTC (9:08 pm CST), a 1.5 mi (2.4 km) wide, EF3 tornado touched down southwest of Pocahontas. Remaining on the ground for over an hour, this tornado meandered along a 30 mi (48 km) path, producing several satellite tornadoes.

Officials blocked off the town and Governor Terry Branstad issued a disaster proclamation for the town. Early estimates indicated that 60% of the town was damaged and 20% was nearly flattened. Despite the damage, only three people sustained minor injuries.

On April 10, another moderate risk was issued. A PDS Tornado Watch was issued for parts of Minnesota, Michigan, and Iowa, as well as most of Wisconsin. With 16 confirmed tornadoes in Wisconsin, the outbreak ranks as the largest single-day event in April in the state. Severe damage occurred in the towns of Merrill, Kaukauna, and Cottonville. On the evening of April 10, a number of tornado watches and warning were issued stretching from southern Oklahoma to Sault. Ste. Marie, Michigan as well as central Ontario which became Canada's first tornado watch of the season. Thunderstorm watches and warnings were also reported as far away as northern and northwestern Ontario.

List of tornadoes

Confirmed tornadoes by Enhanced Fujita rating

EF0	EF1	EF2	EF3	EF4	EF5	Total
7	23	8	4	1	0	43

April 9 event

List of reported tornadoes - Saturday, April 9, 2011
EF#	Location	County	Coord.	Time (UTC)	Path length	Comments/Damage
Iowa
EF3	Mapleton area	Monona		0021	3.5 miles (5.6 km)	Severe damage in town and a state of emergency was declared as a result of a large wedge tornado. Many houses and businesses were damaged or destroyed, with major damage to about 60% of the town and 20% nearly flattened. Severe tree and power line damage occurred as well. About 14 people were injured.
EF1	NW of Ricketts	Crawford	Unknown	0037	0.69 miles (1.11 km)	Brief tornado downed power lines.
EF2	W of Arthur	Ida		0115	4 miles (6.4 km)	Several buildings, including a farm house, were heavily damaged and trees and power lines were damaged. Two grain bins were destroyed as well.
EF3	NW of Odebolt	Sac		0123	10.14 miles (16.32 km)	Large wedge tornado destroyed or badly damaged numerous homes and farms.
EF2	N of Odebolt to Early	Sac		0129	8.34 miles (13.42 km)	High-end EF2 tornado damaged or destroyed several homes and farm buildings. Buildings in downtown Early were badly damaged or destroyed, and several homes were damaged there as well.
EF0	SW of Early	Sac		0138	0.75 miles (1.21 km)	Satellite tornado to the previous storm; executed a small loop in a field shortly after touching down. Caused no damage.
EF1	S of Galva	Ida		0140	unknown	A farmstead was severely damaged with numerous outbuildings destroyed and a home losing its roof. A few other structures, including an ethanol plant, were also damaged.
EF3	SW of Nemaha to SW of Havelock	Sac, Buena Vista, Pocahontas		0208	30 miles (48 km)	Long-track, extremely large wedge tornado, with a damage swath 1.5 miles (2.4 km) wide, leveled several farmhouses and damaged others. Tornado struck the town of Varina, partially destroying a school building and severely damaging several homes. Numerous farm buildings were also damaged or destroyed. Farm equipment was destroyed and trees were snapped and uprooted. Tornado remained on the ground for more than an hour. From 0256 to 0257 UTC (9:56 to 9:57 pm CDT), this was one of five tornadoes on the ground simultaneously in Pocahontas County, all of which were satellite tornadoes to this.
EF2	NW of Nemaha	Sac, Buena Vista		0209	12 miles (19 km)	Large wedge tornado, roughly 0.5 miles (0.80 km) wide, damaged or destroyed several homes and outbuildings.
EF1	S of Cherokee	Cherokee		0220	5 miles (8.0 km)	Several barns and outbuildings sustained significant damage along the tornado's path and corn stubble was scoured. One home sustained roof and window damage and nearby truck trailers were flipped. A confinement building was also destroyed by the tornado. Numerous trees and power poles were snapped as well.
EF2	SW of Pocahontas (2nd tornado)	Sac, Buena Vista,		0224	1.75 miles (2.82 km)	First satellite tornado to the EF3 Varina tornado. Farms were damaged in the area.
EF4	W of Pocahontas (1st tornado)	Pocahontas		0254	3.2 miles (5.1 km)	Second satellite tornado to the EF3 Varina tornado. Strongest tornado of the outbreak with 170 miles per hour (270 km/h) winds. One home was completely leveled by the tornado and swept off its foundation. Trees nearby were snapped and debarked. A combine, estimated at 30,000 pounds (14,000 kg) was tossed roughly 100 yards (91 m) as well.
EF1	WSW of Pocahontas (1st tornado)	Pocahontas		0255	1.5 miles (2.4 km)	Third satellite tornado to the EF3 Varina tornado. On the ground at the same time as the following tornado. Relatively minor damage.
EF1	WSW of Pocahontas	Pocahontas		0255	1.6 miles (2.6 km)	Fourth satellite tornado to the EF3 Varina tornado. Anticyclonic tornado paired with the previous cyclonic tornado. Relatively minor damage.
EF2	W of Pocahontas (2nd tornado)	Pocahontas		0256	0.9 miles (1.4 km)	Fifth satellite tornado to the EF3 Varina tornado. One home was badly damaged.
EF1	W of Pocahontas (3rd tornado)	Pocahontas		0308	2.4 miles (3.9 km)	At least one home was damaged.
EF1	NW of St. Joseph	Kossuth		0419	0.8 miles (1.3 km)	A hog barn was damaged, numerous windows blown out and half of a shed collapsed.
EF0	S of Sulpher Springs	Buena Vista		unknown	1 mile (1.6 km)	Brief tornado with no damage.
EF1	SE of Newell	Buena Vista		unknown	1 mile (1.6 km)	Tornado damaged outbuildings and farm structures.
EF0	SW of Alta (1st tornado)	Buena Vista		unknown	unknown	Brief tornado with no damage. Occurred simultaneously with the other Alta tornado.
EF0	SW of Alta (2nd tornado)	Buena Vista		unknown	unknown	Brief tornado with no damage. Occurred simultaneously with the other Alta tornado.
Sources: NWS Sioux Falls, NWS Omaha, NWS Des Moines

April 10 event

List of reported tornadoes - Sunday, April 10, 2011
EF#	Location	County	Coord.	Time (UTC)	Path length	Comments/Damage
Wisconsin
EF1	SW of Augusta	Eau Claire		2157	1.5 miles (2.4 km)	Brief tornado destroyed a garage and damaged two farmsteads and a barn. Earliest tornado to touch down in Eau Claire County during the course of a year on record. Previous earliest was May 10.
EF1	NW of Augusta	Eau Claire		2204	0.5 miles (800 m)	Two outbuildings destroyed and three more damaged. Significant tree damage as well.
EF3	Merrill area	Lincoln, Marathon		2308	22 miles (35 km)	Severe damage in the area, especially at and around the Merrill Airport where hangars and airplanes were destroyed. Throughout Merrill, 65 homes were damaged or destroyed and three people sustained injuries. One man was thrown 200 ft (61 m) from his home as it was destroyed. Overall damage was estimated at $10.8 million, most of which took place at an industrial park, where multiple large metal buildings were severely damaged. Many trees were snapped and uprooted along the path.
EF2	Cottonville area	Adams		2312	17 miles (27 km)	Homes sustained roof damage and mobile homes were destroyed. Extensive tree damage also occurred along with barns and sheds destroyed. A camping trailer was also overturned and sheet metal was wrapped around trees. A cement silo was blown over and multiple vehicles were flipped. A lake association building was destroyed and irrigation pivots were flipped and twisted. Preliminary losses from the tornado reached $2.25 million.
EF1	SSW of Necedah	Juneau		2314	4.5 miles (7.2 km)	A mobile home was rolled over and pine trees were snapped.
EF1	SW of Hancock	Adams, Waushara		2333	9.3 miles (15.0 km)	Trees and power poles downed. Homes sustained roof damage and irrigation systems were destroyed.
EF1	SE of Parrish	Langlade		2350	5.3 miles (8.5 km)	1 million trees snapped or uprooted and a cabin was destroyed.
EF1	S of Fremont	Waushara, Waupaca		0015	8 miles (13 km)	Multiple barns were destroyed and highway signs were damaged. The roof was torn off one house in Readfield and the steeple was torn off the church.
EF2	E of Argonne	Forest, Florence		0031	13 miles (21 km)	Extensive tree and power line damage. A roof was torn off of a home and several barns and garages were destroyed as well.
EF1	NE of Poy Sippi	Waushara, Winnebago		0053	14.9 miles (24.0 km)	Intermittent tornado touchdown with barns and buildings damaged. Roof damage to homes occurred and extensive tree damage was noted. Crossed over Lake Poygan into Winnebago County where mobile homes were damaged and flipped.
EF1	W of Armstrong Creek	Forest		0108	4.5 miles (7.2 km)	Two homes damaged and a garage was destroyed. Many trees were snapped in the area. Barns were also destroyed.
EF2	Kaukauna area	Outagamie		0144	1.5 miles (2.4 km)	Over 170 houses were damaged in the community, some of them losing roofs. Large trees were uprooted or snapped. A church sustained roof damage and had air conditioning units torn off.
EF1	S of Greenleaf	Brown		0153	1.1 miles (1.8 km)	Silos were damaged and a barn roof was ripped off.
EF1	S of Stockbridge	Calumet		0159	1.1 miles (1.8 km)	Minor damage to 4 homes and the roof was torn off of a metal storage building.
EF0	SSE of Berlin	Green Lake	Unknown	Unknown	2 miles (3.2 km)	Brief tornado damaged a home and tossed furniture. A wooden building was damaged and tree limbs were snapped.
EF0	N of Hamburg	Lincoln, Marathon		unknown	1 mile (1.6 km)	Trees were uprooted and branches were snapped. A home had siding peeled off and several barns were damaged or destroyed.
Missouri
EF0	N of Rogersville	Webster		0355	6 mi (9.7 km)	Damage to trees and outbuildings.
Sources: NWS Twin Cities, NWS La Crosse, NWS Green Bay, NWS Springfield

April 11 event

List of reported tornadoes - Monday, April 11, 2011
EF#	Location	County	Coord.	Time (UTC)	Path length	Comments/Damage
Texas
EF1	NNW of Rio Vista	Johnson		0609	100 yards (91 m)	Five houses were damaged, one of them heavily and a wall was torn from a pharmacy. Mobile homes were also damaged and barns were destroyed. Trees were downed as well.
EF1	W of Alvarado	Johnson		0622	200 yards (180 m)	Mobile homes were flipped and 5 businesses were damaged. 2 people were injured.
EF1	Forney area	Kaufman		0713	0.5 miles (800 m)	Several houses sustained roof damage and a truck stop sign was blown over.
EF1	S of Cash	Hunt		0734	7 miles (11 km)	Two houses were heavily damaged and numerous other houses sustained lesser damage. Mobile homes in the area were badly damaged or destroyed. Sheds and trees were damaged. A pipe manufacturing plant was damaged and 4 trailers were blown across the highway was well.
Alabama
EF1	Vestavia Hills	Jefferson		0027	0.4 miles (640 m)	Brief tornado embedded in larger microburst. One house was heavily damaged and numerous trees were snapped.
Sources: NWS Fort Worth, NWS Birmingham

Non-tornadic events

Accompanying the tornadoes, large hail and high winds also impacted parts of the Midwest. Initially, these events associated with the outbreak were confined to Iowa and parts of Nebraska and Minnesota on April 9. In Iowa, hail was measured up to 3.5 in (8.9 cm) in diameter, resulting in some damage to homes and cars. On April 10, a large line of severe storms produced damage from northern Minnesota southward to the Texas-Mexico border. Most damage along this line resulted from straight-line winds; however, Wisconsin, 2 to 2.5 in (5.1 to 6.4 cm) diameter hail in La Crosse broke windows, dented cars and damaged homes. Roughly 3,200 insurance claims worth $12 million were later made in the city. Elsewhere in the state, winds up to 65 mph (105 km/h) downed numerous trees and power lines and in some instances tore roofs of buildings.

In Texas, winds as high as 95 mph (153 km/h) caused extensive damage to homes and businesses, resulting in roughly $100 million in damage. Numerous trees were felled across the region and a few structures were destroyed. In Dallas County, a few carports collapsed. Near Venus, 82 mph (132 km/h) winds damaged five homes.

On April 11, a strong derecho brought widespread damage to much of northern Alabama as well as parts of Mississippi, Georgia and Tennessee. Near Brent, Alabama, a wind gust of 110 mph (180 km/h) was recorded 70 ft (21 m) up on a radio tower.

Aftermath

Within days of the tornadoes in Iowa, excavators were brought in to clear debris and tear down homes that were damaged beyond repair. On May 5, nearly a month after the outbreak, President Barack Obama signed a federal disaster declaration for Buena Vista, Cherokee, Ida, Monona, Pocahontas and Sac Counties in Iowa. This allowed for government aid to be sent to the region and aid in recovery efforts. This declaration is set to remain in effect until May 1, 2012. A disaster outreach center was opened on May 6 at the Mapleton City Hall and the American Legion Post in Varina and would remain open through May 26. At these places, residents would be allowed to apply for small business and homeowner loans up to $2 million and $200,000 respectively.