April 25-28, 2011 marks a stretch on the calendar known in weather circles for one of the deadliest and most destructive tornado outbreaks in United States history. Storms that occurred during that period killed 321 people and caused over $12 billion in damage. Certainly, in modern times, or at least in our latest 30-year climate period, it is the benchmark.
Prior to 2011, the record number of tornadoes in a whole month was 542, set in May 2004. In comparison, there were 362 confirmed tornadoes, during the four-day stretch now known as the Super Outbreak. This was just the third event since 1932 to be given the designation of Super Outbreak.
April 27 marked the peak of the episode. Despite the continued advancements in technology and increased lead time on warnings through the years, that date was the deadliest due to tornadoes in the United States since 1925. 226 tornadoes caused 316 fatalities in five states.
Photo via NWS Birmingham
Scientists attribute part of the high death toll to chance. In the last Super Outbreak of April 1974, there were even more intense tornadoes. However, there were fewer deaths and damages because the twisters struck fewer urban and suburban areas than the 2011 Super Outbreak.
During the event, four tornadoes garnered the highest possible rating and the tornado damage intensity Enhanced Fujita Scale—EF5. Those tornadoes are believed to produce winds over 200mph. In a typical year, one or fewer tornadoes are assigned that rating. The four EF5’s struck (in order) Philadelphia, MS., Hackleburg-Phil Campbell, AB., Smithville, MS. and Fyffe/Rainsville, AB.
The Philadelphia tornado ripped pavement off of the ground, completely leveled strong brick houses and killed three. The Hackleburg-Phil Campbell twister ripped homes off of strong foundations tossing them several hundred yards, ripped apart and twisted high-voltage power-line trusses and killed 72. Watch some mesmerizing and scary video of that one below. The violent Smithville storm lifted one pickup off of a driveway never to be seen again, completely scoured vegetation from the ground and killed 23. In the Fyffe/Rainsville storm, a school bus was ripped clean off of its frame, trees were debarked and 25 were killed.
This outbreak also produced the infamous EF4 Tuscaloosa, AB. Tornado that would kill 44 and injure 1,000. As it moved through a highly populated area, the storm was well photographed and documented by local TV stations and sky cameras. Some of the most widely renowned and well respected television coverage came from severe weather broadcasting pioneer James Spann of ABC 33/40 in Birmingham, AB. Watch his coverage of the event beginning around the 2:38:00 mark of this video (that’s right, he was live on-air for eight consecutive hours). Whole communities were leveled and debris from the destruction was reported to be falling from the sky over 20 miles away in Birmingham, AB.
Top Left - surface low over northeast Arkansas with very favorable moisture as far north as Tennessee
Top Right - strong upper level winds favorable for long-lived thunderstorms from north Texas through Tennessee
Bottom Left - strong low level winds favorable for rotating thunderstorms from the Mississippi/Alabama coast to Kentucky
Bottom Right - high instability favorable strong thunderstorms from southeast Louisiana to southwest Tennessee
*All images from 4pm on April 27, 2011
The four day event came together as the final in a series of upper level storms moved into the Great Plains. Much colder than its predecessors, the atmosphere was able to rapidly destabilize. An unusually strong surface low pressure system then developed in Arkansas and was steered northeastward. As this storm formed, low-level winds greatly increased. Surface southerly winds of 10-15mph crossed nearly 50mph southwesterly winds aloft. This change of vertical wind speed and direction is known as shear and is an ingredient needed to create highly-organized, rotating storms. A strong jet stream aloft, gave storms plenty of “breathing-room” and ensured that they could move forward for a long duration. The strong southerly winds quickly replenished moisture used by strong morning thunderstorms in southern Mississippi and Alabama. Behind the early storms, clearing allowed maximum sunshine and moisture to rapidly destabilize the atmosphere.
The outbreak was well forecast. Meteorologists saw the setup days in advance issuing their highest severe weather risk and most strongly worded statements. The rarest of National Weather Service (NWS) Storm Prediction Center (SPC) products, the Particularly Dangerous Situation Tornado Watch, which is sometimes seen less than once a year, was used 9 times during the four day event.
Even during the event, NWS maintained an average warning lead time of 24 minutes, allowing those paying attention to alerts to prepare. You always want to have a way to access alerts when severe weather is in the forecast. They are provided via radio, television, weather radio, and cellular devices. These are life-saving announcements and it’s critical to understand what they mean. A watch means that there is potential for dangerous weather to affect your area later. Warnings, however, are issued when severe weather is imminent or already occurring.
As we have said previously, the daily chance of a tornado at any one location certainly is not high enough to ever prevent you from booking travel or events months or years in advance. However, there is some predictability as to where and when tornadoes are most likely–and those areas do shift through the year. YourCast is happy to provide this guidance as you are considering vacation weather and making travel plans.