The Five Year Anniversary of the April 27th, 2011, Tornado Super Outbreak

April 27th, 2016, will be the five year anniversary of the April 27th, 2011, Super Outbreak of tornadoes that occurred across Dixie Alley in the southeastern United States. Between April 26th and April 28th, 2011, there were 363 total tornadoes. On April 27th alone, there were 219 tornadoes. This outbreak surpassed the 1974 Tornado Outbreak that produced 148 tornadoes.

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Mesocyclone (supercell) tracks from April 27th – April 28th, 2011 across the eastern half of the United States. Areas of red and orange indicate the strongest areas of rotation that occurred. Image credit: NOAA/NSSL.

The Enhanced Fujita (EF) Scale is shown below. The number of tornadoes between April 26th and April 28th, 2011, are tabulated according to the strengths that were confirmed by multiple National Weather Service offices.

SCALEWIND SPEED# OF TORNADOESFATALITIESINJURIES
EF-0 65-85MPH134
EF-186-110MPH143
EF-2111-135MPH49
EF-3136-165MPH22
EF-4166-200MPH11
EF-5 >200MPH4
TOTAL TORNADOES3633242,000+

Seven days prior, the first medium range forecasts started to suggest the potential for severe weather across the southeastern U.S. as an upper-level trough was forecasted to dig into the Deep South. Over the next few consecutive days, forecast consensus began to increase, and the threat level for potentially strong to violent tornadoes increased to unprecedented levels.

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The Day 4 and Day 5 severe weather outlooks issued by the Storm Prediction Center prior to April 27th, 2011. Image credit: Storm Prediction Center

The 500mb upper air analysis the night before April 27th showed an impressive dynamic environment as a mid-level jet near 100 knots started to pivot into the region. The morning of April 27th, 2011, the atmosphere was loaded with volatile thermodynamic and dynamic profiles as a powerful low pressure system moved through the Ozark Plateau. The 7:00am CDT morning sounding from Jackson, Mississippi, revealed intense low-level wind shear with strong upper air support. Upon recovery of the atmosphere from severe thunderstorms the morning of, a major outbreak of tornadoes was imminent as atmospheric instability would become extremely unstable.

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7:00am CDT observed sounding from Jackson, Mississippi, on 4/27/11. Image credit: Storm Prediction Center

500mb upper air analysis at 7:00pm CDT, 4/26/11. A strong mid-level jet was beginning to pivot into Dixie Alley. Image credit: Storm Prediction Center

 

 

 

 

 

 

 

 

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The afternoon severe weather outlook on April 27th, 2011. A High Risk was issued by the Storm Prediction Center across portions of Dixie Alley, where a 45% tornado probability was hatched across the High Risk area. Image credit: Storm Prediction Center.

By early afternoon, Particularly Dangerous Situation (PDS) Tornado Watches were issued across Alabama, Mississippi, and Tennessee. The potential was high for the evolution of long-lived supercells that were capable of producing long-track, damaging, strong to violent tornadoes. EF-5 tornadoes impacted the cities of Hackleburg, Alabama; Rainsville Alabama; Philadelphia, Mississippi; and Smithville, Mississippi.

The Hackleburg – Phil Campbell, Alabama, EF-5 tornado: Hackleburg and Phil Campbell, Alabama, were impacted by an extremely violent EF-5 tornado with estimated winds of 210MPH. The tornado formed at 3:05pm CDT and dissipated over two hours later, at 5:40pm CDT. This tornado was on the ground for a staggering 132 miles and had a maximum width of 2,200 yards, or 1.25 miles.

Upon impacting Hackleburg and Phil Campbell, multiple houses were swept completely off their foundations, and vehicles were thrown hundreds of yards from where they once were. The tornado also stripped forests of their trees, and it is something that can still be seen to this day on Google Earth.

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Tornado damage near Phil Campbell, Alabama. Image credit: The Huntsville Times, (Conn, 2011).

The Philadelphia, Mississippi, EF-5 tornado: This was the first EF-5 tornado of the day on April 27th, as denoted by time evolution based on Doppler radar analyses from National Weather Service damage surveys. The tornado had estimated winds of 205MPH, with a maximum width of a 1/2 mile. It was also on the ground for 29 miles.

As the tornado moved through west-central Mississippi and into the Philadelphia area, it reached peak intensity; scouring the ground to a depth of two feet that was 100 yards wide, and 400 yards long. This was also the first EF-5 rated tornado that occurred in Mississippi in nearly 55 years.

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Ground scoured near Philadelphia, Mississippi, from the EF-5 tornado. Image credit: National Weather Service, Jackson, Mississippi

The Smithville, Mississippi, EF-5 tornado: With maximum winds of 205MPH, and a width of 3/4 of a mile wide, the Smithville tornado was a very intense tornado. In Smithville, several brick frame houses were completely destroyed, and hundreds of trees were snapped in half and debarked, resulting in the rating of an EF-5. Additionally, a police station and post office suffered major damage. The tornado was on the ground for 35.1 miles.

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Tornado damage in Smithville, Mississippi. Houses are completely swept off of their foundations. Image credit: National Weather Service, Memphis, Tennessee.

The Rainsville, Alabama, EF-5 tornado: A large, multi-vortex tornado impacted the city of Rainsville, Alabama, at peak intensity with winds over 200MPH. Near peak intensity, it had a maximum width of 3/4 of a mile and was on the ground for 34 miles. Several houses were completely destroyed, hundreds of trees were leveled and debarked, and debris was scattered for miles from the tornado.

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A well constructed house completely swept away; the concrete porch remains. The forest in the background was leveled. Image credit: National Weather Service, Birmingham, Alabama

Several other violent tornadoes occurred, including a significant EF-4 multi-vortex tornado with winds of 190MPH that impacted the Tuscaloosa, Alabama, metropolitan area head on. Near peak intensity, the tornado impacted the University of Alabama and devastated the university. The tornado had a maximum width of 1.5 miles as it crossed Interstate 65 in Tuscaloosa, and it was on the ground for 80 miles.

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Still image from the WBRC News webcam in Tuscaloosa, Alabama, as the tornado moved into the metropolitan area. Image credit: FOX 6 News Tuscaloosa

The April 27th, 2011, Tornado Super Outbreak was the most prominent tornado outbreak in recorded history. In the year of 2011, there were 1897 total tornadoes. 363 of the 1897 tornadoes occurred in a three day span from April 26th, 27th, and 28th, 2011, respectively. Since 1999, there were only three F-5/EF-5 rated tornadoes (the EF-Scale was implemented in 2007) in the United States. If you were to calculate the total number of tornadoes annually over the past decade, the percentage of an EF-5 tornado occurring is in the one thousandth percentile of one percent. Four of them occurred in one day on April 27th, 2011.

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Graph of the recorded tornadoes in 2011 compared to average daily trends from 2005-2010. Image credit: Storm Prediction Center

 

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Annual total tornadoes from 2005-present. Image credit: Storm Prediction Center

In addition to the hundreds of tornadoes that occurred in Dixie Alley on April 27th, 2011, several significant wind and severe hail events. The largest hailstone observed was near Saltville, Maryland, of 4.50″ in diameter (softball size). The top 10 hail reports are shown below. Note that there were several locations that reported destructive hail of up to 3.00″ in diameter.

LocationCountyStateHail Size
SaltvilleSmythVirginia4.50_
HamiltonMarionAlabama4.00_
BatesvillePanolaMississippi4.00_
OkolonaChickasawMississippi3.00_
PocahontasRandolphArkansas2.75_
PolkvilleSmithMississippi2.75_
CordovaWalkerAlabama2.75_
6mi W JasperMarionTennessee2.75_
KnoxvilleKnoxTennessee2.75_
KingsportSullivanTennessee2.75_

Widespread damaging winds occurred across Dixie Alley and the eastern half of the United States. An extremely damaging wind gust of 113MPH was measured at an airport in Craighead County, Arkansas. The majority of the wind reports were unknown in their strength due to the lack of observations. The top 15 wind reports were compiled below (winds in excess of 75MPH are hurricane force).

LocationCountyStateMax Wind
BayCraigheadArkansas113MPH
3mi E HarvestMadisonAlabama80MPH
KnoxvilleKnoxTennessee70MPH
WilliamstownGrantKentucky65MPH
EllsinoreCarterMissouri65MPH
LorentzUpshurWest Virginia64MPH
Max MeadowsWytheVirginia63MPH
2mi ENE New MarketFrederickMaryland63MPH
AlonzavilleShenandoahMaryland62MPH
MyerstownLebanonPennsylvania62MPH
CourtlandLawrenceAlabama62MPH
Muscle ShoalsColbertAlabama60MPH
FranklinWilliamsonTennesseeUnknown / 1 fatal
RomeFloydGeorgiaUnknown / 4 injured
CamdenCamdenNew JerseyUnknown / 2 injured
In all, there were 219 confirmed tornadoes, 438 reports of wind damage, and 207 severe hail reports, on April 27th, 2011. Tornadoes were confirmed from Dixie Alley all the way into north-central New York state as the potent low pressure system progressed through the eastern half of the U.S. This outbreak reached historic levels, and set a record for the most tornadoes in one day in the United States.

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