Never forgotten: Super Outbreak 2011 anniversary
Meteorologist
Thursday, April 26, 2018, 5:53 PM - It's April 25, 2011 and a powerful low pressure system is moving through the southern Plains. The sun is high in the sky, heating the surface and destabilizing the atmosphere. Forecasters expect thunderstorms - strong ones - to spark through the afternoon, anticipating heavy rain, large hail, damaging winds, and tornadoes. But no one knows how intense this outbreak will become. The Super Outbreak of 2011 - the largest, costliest, and one of the deadliest tornado outbreaks in U.S. history - is about to begin.
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By the numbers - remembering the event
- 4 - how many days the event lasted; April 25 to 28 2011
- 4 - the number of tornadoes rated EF5 (the highest rating); all of them happened April 27
- 216 - the number of tornadoes that touched down on April 27 alone, a record
- 317 - the number of fatalities on April 27; the highest number of tornado-related deaths in a single day since the "Tri-State Outbreak" on March 18, 1925
- 334 km/h - the highest recorded winds, associated with one of the EF5 tornadoes in Alabama
- 348 - the number of fatalities associated with the outbreak, 324 considered tornado-related
- 360 - total number of confirmed tornadoes over the 4 days
- $12 billion - the total estimated damages
The Weather setup - was it unique?
A low pressure system in the southern Plains was drawing in moisture from the Gulf of Mexico, raising dew points and temperatures across the Lower Mississippi Valley and along the Gulf Coast on April 25. Forecasters had highlighted the risk of severe weather from Arkansas through Tennessee as the system approached, and on the afternoon of the 25th, the Storm Prediction Center (SPC) issued a Particularly Dangerous Situation (PDS) tornado watch for much of Arkansas and parts of Missouri, Oklahoma, Texas, and Louisiana.
April 26 brought more of the same, with the risk for supercell thunderstorms in the afternoon and a large cluster of storms known as a mesoscale convective complex (MCC) throughout the evening hours. This would normally bring the threat of strong damaging winds. The SPC again highlighted the risk of severe weather for portions of Louisiana, Arkansas, Oklahoma, and Texas along and near the Interstate 30 corridor as conditions became even more favorable for extreme weather. Another large PDS tornado watch was issued for the afternoon.
Severe weather conditions peaked on the 27th, with the SPC and local forecasters anticipating strong to violent long-track tornadoes throughout the afternoon and evening hours. CAPE (convective available potential energy - a measure of the strength of the updraft/buoyancy in the atmosphere) values were forecast to be very high; around 3000–4000 J/kg. Significant severe weather was already ongoing early on April 27 and continued for the entire day.
For the second day in a row, the SPC used their strongest rating - high - in their daily severe weather outlook when discussing the potential for damaging storms across the South. Later that morning, the SPC even increased the probability for tornadoes to 45 percent along a corridor from Meridian, Mississippi, to Huntsville, Alabama, an extremely rare issuance exceeding the high risk standards. Conditions became increasingly favorable for tornadoes during such an extreme tornado outbreak.
Watch below: "A horrific day" TWN meteorologists look at the Tuscaloosa tornado
Tuscaloosa - the deadliest tornado
The 2011 Tuscaloosa tornado was a large and violent EF4 multiple-vortex tornado that devastated portions of Tuscaloosa and Birmingham, Alabama, as well as smaller communities and rural areas between the two cities, during the late afternoon and early evening of Wednesday, April 27, 2011.
Radar and velocity image of the supercell that produced the tornado at 22:10 UTC (5:12 p.m. CDT) as it struck Tuscaloosa, with a debris ball clearly visible. Image courtesy NOAA.
It reached a maximum path width of 2.4 kilometres during its track through Tuscaloosa, it crossed Interstate 65 north of Birmingham, and attained estimated winds of 310 km/h shortly after passing through the city. It then went on to impact parts of Birmingham as a high-end EF4 before dissipating. The tornado killed 46 people and injured more than 1500.
