A tornado outbreak took place on April 9–11, 2011. The outbreak was one of several tornado outbreaks in the United States to take place during the record month of April of that year, 49 tornadoes were produced across the Midwest and Southeast from April 9–11. 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 tornado of the outbreak was an EF4 tornado that touched down west of Pocahontas, Iowa on April 9, a short-lived satellite to a long-track EF3 tornado. Between 9:56 to 9:58 p.m. CDT (02:56 to 02:58 UTC) that day, five tornadoes were on the ground simultaneously in Pocahontas County, Iowa, all of which were from one supercell thunderstorm. Other tornadoes impacted parts of eastern Kentucky and Tennessee on April 9, hours before the event in Iowa.

Throughout Iowa, damage from the storms was estimated at $78.6 million, much of which likely took place in and around Mapleton, which was struck by an EF3 tornado on April 9. 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 sixteen billion dollar disasters in 2011.

Meteorological synopsis A large storm system with an associated frontal boundary moved northward and eastward across the central United States beginning on April 8. While initial severe weather was limited, a lone supercell broke out ahead of a mesoscale convective system in Pulaski County, Virginia on the eastern end of the warm front that evening. Two tornadoes were confirmed, one of which was an EF2 that caused severe damage in Pulaski, Virginia. Numerous houses were damaged and eight people were injured. An outbreak began across the United States during the afternoon of April 9; supercells developed along the warm front and tracked through parts of Kentucky, Tennessee, Virginia, and North Carolina, generating softball sized hail and eight more tornadoes.

At the same time, 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 convective available potential energy (CAPE) 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.

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 22:50 UTC (5:50 p.m. 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. At 00:20 UTC (7:20 p.m. CDT), a small tornado touched down roughly 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 north of Mapleton. A separate EF2 tornado struck the town of Early, where considerable damage occurred to homes and businesses.

Tracking northeastward, the supercell moved into Ida County, another tornado touched down around 01:20 UTC (8:20 p.m. CDT) to the west of Arthur. This storm remained on the ground for eight minutes, during which it damaged a few structures, before dissipating northwest of Arthur. Around the same time, the cell entered Sac County and the first in a series of multiple tornadoes touched down northwest of Odebolt. Over the following three hours, 14 tornadoes touched down across Sac, Buena Vista, and Pocahontas counties. At 02:08 UTC (9:08 p.m. CST), a wide EF3 tornado touched down in northern Sac County. Remaining on the ground for an hour, this tornado meandered along a path, producing several satellite tornadoes, including a short-lived EF4 tornado west of Pocahontas.

Officials blocked off the town and Iowa state 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 ranked 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.Storms cause havoc in Ontario - The Weather Network, April 11, 2011

Confirmed tornadoes

April 9 event + List of confirmed tornadoes – Saturday, April 9, 2011EF#LocationCounty / ParishStateStart Coord.Time (UTC)Path lengthMax widthDamage EF0W of ValeriaMenifee, WolfeKY18:00–18:04Hundreds of trees were damaged in the Daniel Boone National Forest. The path may have been longer but was unable to be surveyed. EF0ValeriaWolfeKY18:05–18:09A well-constructed barn lifted and moved, a well-anchored carport was destroyed, and many large trees were twisted or uprooted. Two houses and a vehicle were also damaged. EF0NortonCity of NortonVA19:45–19:48Two old buildings sustained roof damage and partial wall collapse, and several trees were downed. EF0Milligan CollegeCarterTN20:35–20:40Several trees were downed in the community of Milligan College, just west of Milligan College. EF0NNE of ShelbyClevelandNC20:50–20:51Two mobile homes were flipped over, injuring three of the occupants in one. Several houses sustained minor structural damage, and other mobile homes received mainly minor underskirting and roof damage. The roof was blown off a vehicle shed, and trees were downed. EF1E of JonesboroughWashingtonTN22:00–22:05Three barns were heavily damaged, and numerous trees and power lines were downed. EF1Johnson CityWashingtonTN22:08–22:11Several large trees were knocked down. EF0NNE of Flag PondUnicoiTN22:15–22:20Several trees were downed. EF3MapletonMononaIA00:20–00:26UnknownSee article on this tornado – 14 people were injured. EF1NW of RickettsCrawfordIA00:37–00:38This tornado, which was produced by the same storm as the Mapleton EF3 tornado, knocked down power lines. EF2W of ArthurIdaIA01:20–01:28This tornado occurred between Arthur and Ida Grove, where two grain bins and two outbuildings on a farmstead were either heavily damaged or destroyed, and a house and garage sustained shingle damage. Several trees were downed, and power poles and lines were damaged. EF3NW of Odebolt to E of SchallerSacIA01:23–01:55A large wedge tornado damaged or destroyed several houses and downed power lines. It initially moved northeast toward Early before making a sharp turn north-northwest to just east of Schaller. This tornado occurred simultaneously to and just west of the following tornado. EF2N of Odebolt to N of EarlySacIA01:29–01:54See article on this tornado. EF0SSW of EarlySacIA01:38–01:40This tornado formed as a satellite to the previous tornado. It executed a brief loop and then moved due north before dissipating. It remained primarily over open country. EF1S of GalvaIdaIA01:42–01:47A farmstead was severely damaged, with numerous outbuildings destroyed and a home losing its roof. Outbuildings at another farmstead were damaged, as was an outbuilding at an ethanol plant. At least five power poles were snapped, and trees were downed as well. EF3NNE of Early to NW of PocahontasSac, Buena Vista, PocahontasIA02:08–03:07See article on this tornado – A very large and long lived wedge tornado traversed through three counties, causing severe damage to several farmsteads and the communities of Varina and Ware. EF0S of Sulphur SpringsBuena VistaIA02:14–02:15This brief tornado occurred just a few miles north of the long-track EF3 tornado that began at 02:08 UTC. No damage was reported. EF1SSE of CherokeeCherokeeIA02:20–02:30Several outbuildings were damaged or destroyed on two farmsteads, a camper was flipped into a garage, causing damage to both, a large anchored empty tank was flipped, and several buildings in a livestock confinement area were heavily damaged. A house sustained roof damage and broken windows, a grain bin was blown into a semi truck, and a semi trailer was flipped onto another grain bin. Several trees were snapped or uprooted, corn stubble was scoured, and power poles and lines were damaged. EF2SE of NewellSac, Buena VistaIA02:24–02:27First satellite tornado of the EF3 tornado that touched down at 02:08 UTC. EF1ESE of NewellBuena VistaIA02:25–02:27Several outbuildings and farm structures were damaged. This tornado tracked over the same track of the EF3 tornado that began at 02:08 UTC. EF0SW of AltaBuena VistaIA02:50–02:51A storm chaser reported two simultaneous brief tornadoes with no damage. EF0SW of AltaBuena VistaIA02:50–02:51A storm chaser reported two simultaneous brief tornadoes with no damage. EF4W of PocahontasPocahontasIA02:54–03:01Second satellite tornado of the EF3 tornado that touched down at 02:08 UTC. One farmstead was completely devastated by this violent tornado. EF1WSW of PocahontasPocahontasIA02:55–02:58Third satellite tornado of the EF3 tornado that touched down at 02:08 UTC. This was the cyclonic counterpart of the following, fourth satellite tornado. EF1WSW of PocahontasPocahontasIA02:55–02:58Fourth satellite tornado of the EF3 tornado that touched down at 02:08 UTC. This was the anticyclonic counterpart of the previous, third satellite tornado. EF2W of PocahontasPocahontasIA02:56–02:58Fifth satellite tornado of the EF3 tornado that touched down at 02:08 UTC. This tornado was quickly absorbed by the second, violent EF4 satellite tornado. EF1WNW of PocahontasPocahontasIA03:08–03:13One house was damaged as the tornado remained over mostly open fields. This tornado occurred east of the track of the 02:08 UTC EF3 tornado that had just dissipated to the northwest. EF1WNW of St. JosephKossuthIA04:19–04:21A hog barn was damaged, numerous windows were blown out, and a shed was partially collapsed.

April 10 event