The 2011 Super Outbreak was the largest and costliest tornado outbreak ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25 to 28, 2011, leaving catastrophic destruction in its wake. Over 175 tornadoes struck Alabama, Mississippi, and Tennessee, which were the most severely damaged states. Other destructive tornadoes occurred in Arkansas, Georgia, Kentucky, Louisiana, New York, and Virginia, with storms also affecting other states in the Southern and Eastern United States. In total, 368 tornadoes were confirmed by NOAA's National Weather Service (NWS) and Government of Canada's Environment Canada in 21 states from Texas to New York to southern Canada. Widespread and destructive tornadoes occurred on each day of the outbreak. April 27 was the most active day, with a record 224 tornadoes touching down that day from midnight to midnight CDT (05:00–05:00 UTC). Four of the tornadoes were rated EF5, which is the highest ranking on the Enhanced Fujita scale; typically these tornadoes are recorded no more than once a year, and may not be recorded for several consecutive years.

In total, 348 people were killed as a result of the outbreak, including 324 tornado-related deaths across six states and 24 fatalities caused by other thunderstorm-related events such as straight-line winds, hail, flash flooding or lightning. In Alabama alone, 238 tornado-related deaths were confirmed by the Storm Prediction Center (SPC) and the state's Emergency Management Agency. April 27's 316 fatalities were the most tornado-related fatalities in the United States in a single day since the "Tri-State" outbreak on March 18, 1925 (when at least 751 people were killed). Nearly 500 preliminary local storm reports were received for tornadoes over four days, including 292 in 16 states on April 27 alone. This event was the costliest tornado outbreak in United States history, with total damage reaching $10.2 billion (equivalent to $ billion in ). In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The 2011 Super Outbreak received an OIS of 383, making it the second most intense tornado outbreak in recorded history behind only the 1974 Super Outbreak.

Meteorological synopsis

Setup during April 25–27

The outbreak was caused by a vigorous upper-level trough that moved into the Southern Plains states on April 25. An extratropical cyclone developed ahead of this upper-level trough between northeastern Oklahoma and western Missouri, and moved northeastward. Conditions were similar on April 26, with a predicted likelihood of severe thunderstorms, including an extended threat of strong to violent long-track tornadoes throughout the afternoon and evening; mixed-layer CAPE values were forecast to be around 3000–4000 J/kg, around east Texas, Louisiana, and Arkansas. The storm mode on April 26 was predicted to include mostly discrete tornadic supercells during both the afternoon and the early evening, shifting over to a mesoscale convective complex, with more of a threat of damaging winds and hail during the nighttime.

As the storm system moved eastward toward the Ohio, Mississippi, and Tennessee Valleys on April 27, a very powerful 80–100 knot mid-level jet stream moved into the Ohio and Tennessee Valleys behind the trough and created strong wind shear, along with a low pressure center moving quickly northeastward across those areas on April 27. During the afternoon of April 27, CAPE values were estimated to be in the range of 2000–3000 J/kg across Louisiana and southern Mississippi, with the moderate instability moving northeastward across the southern Tennessee Valley; additionally, temperatures across the southeastern United States ranged from the 70s °F (mid-20s °C) to the lower 90s °F (near 35 °C). Helicity levels ranged from 450 to 600 m2/s2, which supported some significant tornadic activity and strong to violent long-track tornadoes. At 06:10 UTC, the SPC issued a second-consecutive, high risk day-one outlook, featuring a 30% hatched risk of tornadoes centered over northern Alabama. At 16:30 UTC (11:30 AM CDT) this region was expanded to include portions of eastern Mississippi, southern Tennessee, and northwest Georgia. Additionally, a rare, 45% hatched risk of tornadoes was introduced along a corridor from Meridian, Mississippi, to Huntsville, Alabama.

Overview

A total of 56 severe weather watches were issued by the Storm Prediction Center (SPC) over those four days in the outbreak area. This included 41 tornado watches—10 of which were particularly dangerous situation (PDS) watches—and 15 severe thunderstorm watches. The SPC assigns numbers to each severe weather watch issued starting at the beginning of each year; the organization accidentally skipped over two of their allocated watch numbers during this outbreak (numbers 208 and 209). The Storm Prediction Center received 292 reports of tornadoes in the preceding 24 hours. In addition to setting the record for most tornadoes in a calendar day (223; midnight to midnight CDT (05:00 – 05:00 UTC)), it also broke the record for the most tornado touchdowns in any 24-hour period with 226 from 12:40 a.m. to 12:40 a.m. CDT (05:40 – 05:40 UTC) April 27–28, breaking the old 24-hour record of 148 set by the 1974 Super Outbreak. Of those 226 tornadoes, 59 touched down in Alabama and 83 began in Tennessee, accounting for 62.8 percent of the tornadoes that touched down on April 27. On April 27 alone, the National Weather Service in Huntsville, Alabama, issued 92 tornado warnings, 31 severe thunderstorm warnings, and seven flash flood warnings. The National Weather Service in Birmingham, Alabama issued 49 tornado warnings, and 24 severe thunderstorm warnings. In total, 449 tornado warnings were issued on April 27

Confirmed tornadoes

+ Daily statistics during the 2011 Super Outbreak DateTotalEF-scale ratingDeathsInjuries EF0  EF1  EF2  EF3  EF4  EF5  April 254217204100559 April 26553119410004 April 2722472*8136201143162,986+ April 284718235100351 Total368EF0138*EF1143EF249EF323EF411EF543243,100+ * One tornado touched down in Ontario, Canada on April 27 and was rated as an F0. It is counted as an EF0 in this table.

A record 368 tornadoes touched down over the span of four days, 37 of which were EF3+ tornadoes. Four tornadoes were rated EF5 – behind only the 1974 Super Outbreak (7 F5s). Several of the strong to violent tornadoes that formed were exceptionally long-tracked, with six tornadoes on April 27 tracking over . Many tornadoes on the afternoon of April 27 were spawned from a collection of supercells that moved across Mississippi, Alabama, Tennessee, and Georgia.

The period from 2:28 p.m. CDT (1928 UTC) to 9:10 p.m. CDT (0210 UTC) represented nearly seven hours of continuous tornado activity during the height of the outbreak of April 27, during which 94 tornadoes touched down. All fifteen violent EF4+ tornadoes occurred continuously during this time, beginning with the Philadelphia, Mississippi EF5 tornado at 2:30 p.m. CDT (1930 UTC) and concluding with the dissipation of the Lake Martin, Alabama EF4 tornado at 9:09 p.m. CDT (0209 UTC). Several tornadoes from the outbreak were exceptionally long-tracked. Three tornadoes on April 27 travelled over , with a fourth traversing . Seven tornadoes–the Vilonia tornado on April 25 and six tornadoes on April 27–stayed on the ground for over an hour. The long-track Mississippi-Alabama EF4 was down from 2 hours, 53 minutes, the longest duration for a tornado in the outbreak.

Ferndale–Vilonia, Arkansas

The first tornado of the outbreak to cause more than one death was this long-tracked, extremely large, and destructive high-end EF2 wedge tornado that struck the small town of Vilonia in Faulkner County, Arkansas, around 7:30 p.m. CDT (00:30 UTC) on April 25. A tornado warning was issued for the area roughly 30 minutes prior to the tornado's arrival, and the relatively low loss of life was attributed to this lead time. A tornado emergency was declared at 7:24 p.m. CDT (00:24 UTC) for the city shortly before the tornado struck. Four people were killed in the town and many more were injured. The tornado touched down northwest of Ferndale in Pulaski County at 6:48 p.m. CDT (23:48 UTC), downing trees and transmission towers at EF1 intensity. It continued northeast of Natural Steps, severely damaging a small church and downing numerous trees, one of which landed on a house. The tornado continued to knock down trees as it passed near Roland, several of which landed on homes. The tornado reached EF2 strength as it crossed into Faulkner County and passed southeast of Mayflower, downing numerous trees and power lines and damaging homes and outbuildings. Past Mayflower, it continued towards Vilonia and struck a mobile home park, where numerous mobile homes were destroyed and the four fatalities occurred. Two of the fatalities occurred when a couple attempted to take shelter in a cargo container, which was thrown and deposited near a pond. Several other people were injured in this area as well. The tornado maintained EF2 intensity as it moved directly through Vilonia, damaging numerous homes and businesses and flipping several semi-trucks. The American Red Cross indicated that approximately 34 site-built houses and 62 mobile homes were destroyed, 91 site-built homes and 41 mobile homes suffered major damage, 145 site-built houses and 43 mobile homes had minor damage, and 53 site-built houses and 38 mobile homes were affected in some other way in the Vilonia area. One of the mobile homes was picked up and flipped, and the home's two bathtubs were found over a hill about away. The lone occupant of the mobile home sustained major injuries. After moving through Vilonia, the tornado weakened to EF1 strength as it moved into White County and passed west of El Paso, where trees were blown over onto houses (damaging several roofs), barns and outbuildings were destroyed, an RV and the trailer portion of a tractor-trailer were overturned, and hundreds of trees were downed. The tornado finally dissipated north of Joy at 7:59 p.m. CDT (00:59 UTC), after having travelled just over . At its widest point, the tornado was wide. Following the tornado, 85 members of the U.S. National Guard were deployed to assist in search and rescue, debris clearing, security and traffic control.

On April 27, 2014, three years and two days after this tornado, a violent EF4 tornado touched down west of Ferndale and moved along almost the same path as this tornado, causing 16 fatalities and many injuries. However, it affected more of Mayflower than this tornado did and caused greater damage all along the path, especially in Vilonia, before lifting near El Paso.

Philadelphia–Kemper County, Mississippi

This violent, fast moving and destructive tornado, which became the first EF5 tornado of the outbreak, touched down near the city of Philadelphia, Mississippi, on April 27. The tornado touched down at 2:30 p.m. CDT (19:30 UTC) and traveled for nearly through Neshoba, Kemper, Winston, and Noxubee Counties, reaching a maximum width of a . The tornado killed three people, injured eight others, and caused $1.1 million in damage across its path.