Tornado outbreak of April 9–11, 2011 explained

Tornado outbreak of April 9–11, 2011
Type:Tornado outbreak
Active:April 9 – April 11, 2011
Tornadoes:49
Fujitascale:EF4
Tornado Duration:54 hours, 31 minutes
Casualties:0 deaths, 21 injuries
Damages:$2.2 billion
Enhanced:yes
Partof:the tornado outbreaks of 2011

One of several tornado outbreaks in the United States to take place during the record month of April 2011, 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 0256 and 0258 UTC (9:56 and 9:58 p.m. CDT) 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.[1] 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.[2]

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.[3] 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.[4]

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.[5] A warm front began developing along the southeastern side of the low pressure area as it moved over The Dakotas.[6]

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.[7] 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 2miles 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 1miles north of Mapleton. A separate EF2 tornado struck the town of Early, where considerable damage occurred to homes and businesses.[8]

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.[9] This storm remained on the ground for eight minutes, during which it damaged a few structures, before dissipating 2miles northwest of Arthur.[10] 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 1.5miles wide EF3 tornado touched down in northern Sac County. Remaining on the ground for an hour, this tornado meandered along a 30miles path, producing several satellite tornadoes, including a short-lived EF4 tornado west of Pocahontas.[11]

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.[12]

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.[13] 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.[14]

Confirmed tornadoes

April 9 event

List of confirmed tornadoes – Saturday, April 9, 2011
EF#LocationCounty / ParishStateStart Coord.Time (UTC)Path lengthMax widthDamage
EF0W of ValeriaMenifee, WolfeKY18:00–18:040.25abbr=onNaNabbr=on250abbr=onNaNabbr=on
Hundreds of trees were damaged in the Daniel Boone National Forest. The path may have been longer but was unable to be surveyed.[15]
EF0ValeriaWolfeKY18:05–18:090.25abbr=onNaNabbr=on100abbr=onNaNabbr=on
A 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.[16]
EF0NortonNorton (city)VA19:45–19:480.37abbr=onNaNabbr=on40abbr=onNaNabbr=on
Two old buildings sustained roof damage and partial wall collapse, and several trees were downed.[17]
EF0Milligan CollegeCarterTN20:35–20:400.89abbr=onNaNabbr=on50abbr=onNaNabbr=on
Several trees were downed in the community of Milligan College, just west of Milligan College.[18]
EF0NNE of ShelbyClevelandNC20:50–20:510.53abbr=onNaNabbr=on75abbr=onNaNabbr=on
Two 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.[19]
EF1E of JonesboroughWashingtonTN22:00–22:053abbr=onNaNabbr=on150abbr=onNaNabbr=on
Three barns were heavily damaged, and numerous trees and power lines were downed.[20]
EF1Johnson CityWashingtonTN22:08–22:110.61abbr=onNaNabbr=on100abbr=onNaNabbr=on
Several large trees were knocked down.[21]
EF0NNE of Flag PondUnicoiTN22:15–22:201.04abbr=onNaNabbr=on50abbr=onNaNabbr=on
Several trees were downed.[22]
EF3MapletonMononaIA00:20–00:263.38abbr=onNaNabbr=on1200abbr=onNaNabbr=onUnknown
A large tornado caused severe damage in Mapleton. Over 100 homes and businesses were damaged or destroyed, representing about 60% of the town. Most garages and other small structures were destroyed, large trees were uprooted, and windows were blown out of vehicles. Fourteen people were injured. A state of emergency was declared as a result of the tornado.[23]
EF1NW of RickettsCrawfordIA00:37–00:380.69abbr=onNaNabbr=on75abbr=onNaNabbr=on
This tornado, which was produced by the same storm as the Mapleton EF3 tornado, knocked down power lines.[24]
EF2W of ArthurIdaIA01:20–01:284.13abbr=onNaNabbr=on440abbr=onNaNabbr=on
This 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.[25]
EF3NW of Odebolt to E of SchallerSacIA01:23–01:5510.14abbr=onNaNabbr=on1760abbr=onNaNabbr=on
A 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.[26] [27]
EF2N of Odebolt to N of EarlySacIA01:29–01:548.34abbr=onNaNabbr=on660abbr=onNaNabbr=on
Numerous houses were damaged or destroyed. The tornado dissipated immediately after passing through Early.[28]
EF0SSW of EarlySacIA01:38–01:400.75abbr=onNaNabbr=on100abbr=onNaNabbr=on
This 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.[29]
EF1S of GalvaIdaIA01:42–01:474.21abbr=onNaNabbr=on200abbr=onNaNabbr=on
A 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.[30]
EF3NNE of Early to NW of PocahontasSac, Buena Vista, PocahontasIA02:08–03:0730abbr=onNaNabbr=on2640abbr=onNaNabbr=on
A very large, long-tracked wedge tornado leveled several farmhouses and damaged several others. Numerous farm buildings, silos, farm equipment, and livestock shelters were also damaged or destroyed. Numerous power poles and lines were blown down, along with many trees. The tornado remained on the ground for an hour and reached a maximum width of 1.5miles in Pocahontas County. It was associated with six satellite tornadoes, including two simultaneous in Buena Vista County and four simultaneous in Pocahontas County, with five tornadoes on the ground at one time from 02:56–02:58 UTC. This tornado took a very erratic path, turning eastward and northward along a northeasterly track, producing an unusual and varying debris field; the track ended just west-southwest of Havelock.[31]
EF0S of Sulphur SpringsBuena VistaIA02:14–02:150.53abbr=onNaNabbr=on50abbr=onNaNabbr=on
This brief tornado occurred just a few miles north of the long-track EF3 tornado that began at 02:08 UTC. No damage was reported.[32]
EF1SSE of CherokeeCherokeeIA02:20–02:305.17abbr=onNaNabbr=on300abbr=onNaNabbr=on
Several 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 damage.[33]
EF2SE of NewellSac, Buena VistaIA02:24–02:271.75abbr=onNaNabbr=on220abbr=onNaNabbr=on
This was the first satellite tornado to the long-track EF3 tornado that began at 02:08 UTC. The tornado moved due east before hooking to the north-northwest into Buena Vista County and dissipating. Farm buildings were heavily damaged, and trees were downed.[34]
EF1ESE of NewellBuena VistaIA02:25–02:271.08abbr=onNaNabbr=on150abbr=onNaNabbr=on
Several outbuildings and farm structures were damaged. This was a satellite tornado to the long-track EF3 tornado that began at 02:08 UTC.[35]
EF0SW of AltaBuena VistaIA02:50–02:510.17abbr=onNaNabbr=on50abbr=onNaNabbr=on
A storm chaser reported two simultaneous brief tornadoes with no damage.[36]
EF0SW of AltaBuena VistaIA02:50–02:510.17abbr=onNaNabbr=on50abbr=onNaNabbr=on
A storm chaser reported two simultaneous brief tornadoes with no damage.[37]
EF4W of PocahontasPocahontasIA02:54–03:013.2abbr=onNaNabbr=on587abbr=onNaNabbr=on
The strongest tornado of the outbreak, rated low-end EF4, was an intense satellite tornado that occurred on the west flank of the large EF3 wedge tornado that began at 02:08 UTC. The tornado moved to the east-southeast, absorbing the 02:56 UTC EF2 tornado that formed as another satellite. One house was flattened and swept off its foundation by this tornado. A combine, estimated at 30000lb, sitting in a machine shed was tossed roughly 100yd, and many trees were debarked.[38] [39]
EF1WSW of PocahontasPocahontasIA02:55–02:581.58abbr=onNaNabbr=on100abbr=onNaNabbr=on
This satellite tornado to the long-track EF3 wedge tornado was on the ground at the same time as the following tornado. Relatively minor damage occurred. Both tornadoes moved generally northward just to the southeast of the 02:08 parent EF3 tornado and the 02:56 UTC EF2 satellite.[40]
EF1WSW of PocahontasPocahontasIA02:55–02:581.64abbr=onNaNabbr=on100abbr=onNaNabbr=on
This satellite tornado to the long-track EF3 wedge tornado was an anticyclonic tornado paired with the previous cyclonic tornado. Relatively minor damage occurred. Both tornadoes moved generally northward just to the southeast of the 02:08 parent EF3 tornado and the 02:56 UTC EF2 satellite.[41]
EF2W of PocahontasPocahontasIA02:56–02:580.9abbr=onNaNabbr=on146abbr=onNaNabbr=on
This satellite tornado to the long-track EF3 wedge tornado took a curved path northward on the west side of the parent tornado and was quickly absorbed by the eastward moving EF4 satellite. One home was severely damaged.[42]
EF1WNW of PocahontasPocahontasIA03:08–03:132.42abbr=onNaNabbr=on250abbr=onNaNabbr=on
One house was damaged as the tornado remained over mostly open fields. This tornado occurred east of the track of the 02:08 UTC EF3 wedge tornado that had just dissipated to the northwest.[43]
EF1WNW of St. JosephKossuthIA04:19–04:210.79abbr=onNaNabbr=on100abbr=onNaNabbr=on
A hog barn was damaged, numerous windows were blown out, and a shed was partially collapsed.[44]

April 10 event

List of confirmed tornadoes – Sunday, April 10, 2011
EF#LocationCounty / ParishStateStart Coord.Time (UTC)Path lengthMax widthDamage
EF1SW of AugustaEau ClaireWI21:57–22:031.58abbr=onNaNabbr=on200abbr=onNaNabbr=on
Two farmsteads were impacted, with many trees downed. At one, a garage was destroyed, and a barn was heavily damaged as well. This was the earliest tornado to touch down in Eau Claire County on record; the previous earliest was May 10.[45]
EF1NW of AugustaEau ClaireWI22:04–22:060.74abbr=onNaNabbr=on150abbr=onNaNabbr=on
Two outbuildings destroyed, three more were heavily damaged, and numerous trees and power poles were snapped.[46]
EF3N of Hamburg to NE of MerrillMarathon, LincolnWI23:08–23:4121.15abbr=onNaNabbr=on1050abbr=onNaNabbr=on
Severe damage occurred on the north side of Merrill, especially at and around the Merrill Municipal Airport, where hangars and airplanes were destroyed. Throughout Merrill, 65 houses and 12 businesses were damaged or destroyed, with several homes losing nearly all exterior and some interior walls. One person was thrown 200feet after the tornado destroyed his home; he sustained serious injuries. Another person sustained minor injuries. An industrial park sustained heavy damage, and a few other homes and barns were damaged outside of Merrill. Many trees were downed along the path as well.[47] [48]
EF2W of Arkdale to ENE of CottonvilleAdamsWI23:12–23:3017.08abbr=onNaNabbr=on800abbr=onNaNabbr=on
Numerous houses sustained roof and structural damage, and mobile homes were either heavily damaged or destroyed, along with barns and sheds. A camping trailer was also overturned and sheet metal was wrapped around trees. A lake association building was completely destroyed, a cement silo was knocked over, vehicles were flipped, and numerous center-pivot irrigation systems were twisted or destroyed. Numerous trees were downed along the path.[49] [50] [51]
EF1S of NecedahJuneauWI23:14–23:214.37abbr=onNaNabbr=on150abbr=onNaNabbr=on
A mobile home was rolled over, and pine trees were snapped.[52]
EF1SW of HancockAdams, WausharaWI23:30–23:4211.73abbr=onNaNabbr=on140abbr=onNaNabbr=on
Several houses sustained roof damage, the roof was torn off a mobile home, and several center-pivot irrigation systems were destroyed. Trees and power poles were downed as well.[53]
EF1SE of ParrishLangladeWI23:50–23:585.3abbr=onNaNabbr=on400abbr=onNaNabbr=on
This tornado produced extensive tree damage along the path, affecting over 1600acres and knocking down or damaging over one million trees. One cabin was destroyed by falling trees.[54]
EF1Saxeville to Fremont to SE of HortonvilleWaushara, Waupaca, OutagamieWI00:06–00:4327.68abbr=onNaNabbr=on200abbr=onNaNabbr=onUnknown
Multiple barns and other farm buildings were heavily damaged or destroyed, and highway signs were damaged. The roof was torn off a house in Readfield, and the steeple was torn off a church. Many trees were snapped or uprooted along the path.[55]
EF2SE of Argonne to SE of Popple RiverForest, FlorenceWI00:30–00:5111.97abbr=onNaNabbr=on600abbr=onNaNabbr=on
Hundreds of trees were snapped or uprooted, some of which fell on cabins. A roof was torn off of a home, several barns and garages were destroyed, and power lines were downed as well.[56]
EF1Poy Sippi to W of WinchesterWaushara, WinnebagoWI00:53–01:0714.93abbr=onNaNabbr=on150abbr=onNaNabbr=on
Near Poy Sippi, a house was damaged, and a barn was destroyed. Along the north shore of Lake Poygan, another barn was flattened. Near Boom Bay in Winnebago County, two homes lost portions of their roofs, while several other houses sustained minor damage. Two small mobile homes were rolled as well. Many trees were snapped or uprooted along the path.[57]
EF1W of Armstrong CreekForestWI01:03–01:083.29abbr=onNaNabbr=on250abbr=onNaNabbr=on
A garage was destroyed, and two houses were damaged, one of which sustained significant roof damage. Many trees were snapped or uprooted as well.[58]
EF0SE of BerlinGreen LakeWI01:27–01:291.83abbr=onNaNabbr=on50abbr=onNaNabbr=on
Lawn furniture was sucked from under a porch and thrown against a fence, an outdoor spa was damaged, and a wooden structure received light damage. Trees and tree branches were snapped as well.[59]
EF2KaukaunaOutagamieWI01:43–01:461.52abbr=onNaNabbr=on175abbr=onNaNabbr=on
Over 180 houses were impacted in Kaukauna, several of them losing large sections of their roofs. In total, seven homes were destroyed, 24 homes and four businesses sustained major damage, and 160 other homes sustained minor damage. A church sustained roof damage and had air conditioning units torn off, and large trees were snapped or uprooted.[60]
EF1S of GreenleafBrownWI01:53–01:551.2abbr=onNaNabbr=on75abbr=onNaNabbr=on
The tops of two silos were damaged, and a barn roof was ripped off.[61]
EF1S of StockbridgeCalumetWI01:59–02:011.67abbr=onNaNabbr=on100abbr=onNaNabbr=on
A waterspout moved onshore from Lake Winnebago and damaged two homes. A three-season room on one of the houses was ripped off the structure. It also tore off a section of the roof of a large metal outbuilding and snapped the tops of trees.[62]
EF0NNE of RogersvilleWebsterMO03:55–04:036.67abbr=onNaNabbr=on100abbr=onNaNabbr=on
Outbuildings were damaged, and trees were downed.[63]

April 11 event

List of confirmed tornadoes – Monday, April 11, 2011
EF#LocationCounty / ParishStateStart Coord.Time (UTC)Path lengthMax widthDamage
EF1NNW of Rio VistaJohnsonTX06:09–06:131.51abbr=onNaNabbr=on100abbr=onNaNabbr=on
Five houses were damaged, one of them heavily, and a wall was torn from a pharmacy. A garage was shifted off its foundation, and several trees were downed.[64]
EF1AlvaradoJohnsonTX06:22–06:230.13abbr=onNaNabbr=on50abbr=onNaNabbr=on
Five commercial buildings were damaged, and a mobile home was flipped. Two people were injured.[65]
EF1Northern ForneyKaufmanTX07:13–07:170.53abbr=onNaNabbr=on60abbr=onNaNabbr=on
Five houses sustained roof damage, and a truck stop sign was blown over.[66]
EF1Cash to NW of Lone OakHuntTX07:34–07:486.53abbr=onNaNabbr=on200abbr=onNaNabbr=on
Eight homes, a pipe manufacturing plant, and two metal buildings were damaged in Cash, while four U-Haul trailers were blown across the highway. Several more homes sustain mainly minor roof damage to the northeast of Cash, although one home sustained significant damage to the roof and second story. Northwest of Lone Oak, five mobile homes were damaged or destroyed, and another site-built home sustained significant damage. Trees were downed along the path.[67]
EF1Vestavia HillsJeffersonAL00:30–00:310.38abbr=onNaNabbr=on100abbr=onNaNabbr=on
This brief tornado was embedded in a larger microburst. Several homes and other buildings were damaged, mostly by falling trees, and the windows were blown out of a vehicle. Numerous trees were snapped or uprooted as well.[68]

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 3.5inches in diameter, resulting in some damage to homes and cars.[9] 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, 2to diameter hail in La Crosse broke windows, dented cars and damaged homes.[69] Roughly 3,200 insurance claims worth $12 million were later made in the city.[70] Elsewhere in the state, winds up to 65mph downed numerous trees and power lines and in some instances tore roofs of buildings.[71]

In Texas, winds as high as 95mph caused extensive damage to homes and businesses, resulting in roughly $100 million in damage.[72] [73] Numerous trees were felled across the region and a few structures were destroyed. In Dallas County, a few carports collapsed. Near Venus, 82mph winds damaged five homes.[71]

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 110mph was recorded 70feet up on a radio tower.[71]

Aftermath

Within days of the tornadoes in Iowa, excavators were brought in to clear debris and tear down homes that were damaged beyond repair.[74] 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.[75] The declaration remained in effect until May 1, 2012.[76] 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.[77]

See also

Notes and References

  1. News: Nancy Gaarder . Omaha World-Herald . May 6, 2011 . May 14, 2011 . Aid on way for April storms . dead . https://archive.today/20240522200906/https://www.webcitation.org/5yfz8jhN6?url=http://www.omaha.com/article/20110506/NEWS01/705079832 . May 22, 2024 .
  2. Web site: National Climatic Data Center. 2011. November 12, 2011. Billion Dollar U.S. Weather/Climate Disasters.
  3. Web site: NWS Blacksburg. National Weather Service. April 9, 2011. April 9, 2011. Multiple tornadoes confirmed on April 8, 2011.
  4. Web site: Storm Prediction Center. National Oceanic and Atmospheric Administration. April 11, 2011. April 11, 2011. Storm Reports for April 9, 2011.
  5. Web site: Mark Darrow and Melissa Hurlbut. Storm Prediction Center. National Oceanic and Atmospheric Administration. April 9, 2011. April 14, 2011. Apr 9, 2011 0600 UTC Day 1 Convective Outlook.
  6. Web site: Elizabeth Stoppkotte and John Hales. Storm Prediction Center. National Oceanic and Atmospheric Administration. April 9, 2011. April 14, 2011. Apr 9, 2011 1630 UTC Day 1 Convective Outlook.
  7. Web site: Sarah Corfidi. Storm Prediction Center. National Oceanic and Atmospheric Administration. April 9, 2011. May 14, 2011. Tornado Watch 116. https://web.archive.org/web/20110419203220/http://www.spc.noaa.gov/products/watch/ww0116.html. 19 April 2011 . live.
  8. Web site: National Weather Service Office in Omaha, Nebraska . National Oceanic and Atmospheric Administration . April 10, 2011 . May 14, 2011 . Tornado Damage In Monona County, Iowa, Including Mapleton . https://web.archive.org/web/20110615044344/http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=oax&storyid=66512&source=0 . dead . June 15, 2011 .
  9. Web site: Storm Prediction Center. National Oceanic and Atmospheric Administration. April 19, 2011. May 14, 2011. April 9, 2011 Storm Reports. https://web.archive.org/web/20110419192837/http://www.spc.noaa.gov/climo/reports/110409_rpts.html. 19 April 2011 . live.
  10. Web site: National Weather Service Office in Omaha, Nebraska. National Oceanic and Atmospheric Administration. April 21, 2011. May 14, 2011. Damage survey for Arthur, Iowa and Cherokee County tornado.
  11. Web site: National Weather Service Office in Des Moines, Iowa. National Oceanic and Atmospheric Administration. May 3, 2011. May 14, 2011. Tornado Damage Survey April 9, 2011  - Pocahontas Tornado Upgraded to EF4.
  12. Web site: Unattributed . Associated Press . April 10, 2011 . April 10, 2011 . Mayor: Over half of Iowa town damaged by tornado . dead . https://web.archive.org/web/20110413072313/http://www.google.com/hostednews/ap/article/ALeqM5jLdvw3OLD98u83VUN4OJiQ18padw?docId=643922f7ef8c4fb488558570e56e77fa . April 13, 2011 .
  13. News: John Rondy . Reuters . April 11, 2011 . April 12, 2011 . Possible seven Wisconsin tornadoes may be record . live . https://web.archive.org/web/20110414033854/http://www.reuters.com/article/2011/04/11/us-weather-damage-idUSTRE73A4GJ20110411 . April 14, 2011 .
  14. http://www.theweathernetwork.com/news/storm_watch_stories3&stormfile=storms_cause_havoc_in_ontari_110411?ref=ccbox_weather_topstories Storms cause havoc in Ontario
  15. Kentucky Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  16. Kentucky Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  17. Virginia Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  18. Tennessee Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  19. North Carolina Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  20. Tennessee Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  21. Tennessee Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  22. Tennessee Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  23. Iowa Event Report: EF3 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  24. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  25. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  26. The April 9, 2011 NW Iowa Tornado Outbreak. National Oceanic and Atmospheric Administration. National Weather Service Forecast Office in Des Moines, Iowa. 2011. April 19, 2022.
  27. Iowa Event Report: EF3 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  28. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  29. Iowa Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  30. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  31. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022. Iowa Event Report: EF3 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  32. Iowa Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  33. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  34. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  35. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  36. Iowa Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  37. Iowa Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  38. News: Melanie S. Welte . Chicago Tribune . May 3, 2011 . May 4, 2011 . Strength of tornado in Pocahontas County raised . dead . https://web.archive.org/web/20220422010047/http://www.chicagotribune.com/news/chi-ap-ia-iowatornado,0,4970490.story . April 22, 2022 .
  39. Iowa Event Report: EF4 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  40. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  41. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  42. Iowa Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  43. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  44. Iowa Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  45. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  46. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  47. Web site: Unattributed . Green Bay Post-Gazette . April 12, 2011 . April 12, 2011 . Merrill tornado causes $11M damage, hurls man 200 feet . dead . https://archive.today/20240522200827/https://www.webcitation.org/5xuia3vN0?url=http://www.thenorthwestern.com/article/20110412/OSH0101/304130036/Update-Merrill-tornado-causes-11M-damage-hurls-man-200-feet%3Fodyssey=tab%7Ctopnews%7Cimg%7CFRONTPAGE . May 22, 2024 .
  48. Wisconsin Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF3 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  49. News: Jeff Starck . Green Bay Press-Gazette . April 11, 2011 . April 12, 2011 . Merrill tornado damages 65 homes, causes millions in damages . dead . https://archive.today/20240522200705/https://www.webcitation.org/5xtA0CbT6?url=http://www.greenbaypressgazette.com/article/20110411/GPG0101/110411067/0/PKR01/Merrill-tornado-damages-65-homes-causes-millions-damages%3Fodyssey=nav%7Chead . May 22, 2024 .
  50. Web site: Adam Wise . Green Bay Post-Gazette . April 11, 2011 . April 12, 2011 . Tornado causes more than $2 million in damage . dead . https://archive.today/20240522200744/https://www.webcitation.org/5xtAGayUv?url=http://www.wisconsinrapidstribune.com/article/20110412/WRT0101/104120601/Tornado-causes-more-than-2-million-damage%3Fodyssey=tab%7Ctopnews%7Ctext%7CWRT-News . May 22, 2024.
  51. Wisconsin Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  52. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  53. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  54. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  55. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  56. Wisconsin Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  57. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 20, 2022.
  58. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  59. Wisconsin Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  60. Wisconsin Event Report: EF2 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  61. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  62. Wisconsin Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  63. Missouri Event Report: EF0 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  64. Texas Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  65. Texas Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  66. Texas Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  67. Texas Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  68. Alabama Event Report: EF1 Tornado. National Oceanic and Atmospheric Administration. National Climatic Data Center. 2011. April 19, 2022.
  69. Web site: Storm Prediction Center. National Oceanic and Atmospheric Administration. April 20, 2011. May 31, 2011. April 10, 2011 Storm Reports. https://web.archive.org/web/20110614005055/http://www.spc.noaa.gov/climo/reports/110410_rpts.html. 14 June 2011 . live.
  70. Web site: Paul Gores. Milwaukee-Wisconsin Journal Sentinel. May 29, 2011. May 31, 2011. Spring storms take toll on insurers.
  71. Web site: National Weather Service Office in San Diego, California. National Oceanic and Atmospheric Administration. April 2011. May 31, 2011. Hail, Thunderstorm Wind Damage & Thunderstorm Wind Gust events for the U.S. .
  72. Web site: National Weather Service Office in Fort Worth, Texas. National Oceanic and Atmospheric Administration. April 13, 2011. May 31, 2011. April 10-11, 2011 North Texas Severe Storms .
  73. Web site: Shane Allen. NBC Dallas-Fort Worth. April 13, 2011. April 14, 2011. Strong Storms, Tornadoes Cause Estimated $100M in Damages .
  74. News: Dolly A. Butz . Quad City Times . April 18, 2011 . May 14, 2011 . Feds, state officials tour Mapleton . dead . https://web.archive.org/web/20180703062445/https://qctimes.com/news/local/article_74cacdb4-6a33-11e0-9f7f-001cc4c002e0.html . July 3, 2018 .
  75. Web site: Federal Emergency Management Agency . May 5, 2011 . May 14, 2011 . President Declares Major Disaster for Iowa . dead . https://web.archive.org/web/20110828194902/http://www.fema.gov/news/newsrelease.fema?id=54739 . August 28, 2011 .
  76. Web site: Federal Emergency Management Agency . May 5, 2011 . May 14, 2011 . Declaration Detail: M1977 .
  77. News: Unattributed . The Des Moines Register . May 6, 2011 . May 14, 2011 . SBA offers loans for tornado recovery . dead . https://archive.today/20240522200944/https://www.webcitation.org/5yg14cvbj?url=http://www.desmoinesregister.com/article/20110506/NEWS/105060338/-1/GETPUBLISHED03/SBA-offers-loans-tornado-recovery . May 22, 2024 .

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