Some 350 or so tornadoes — roughly 25 percent of which were strong/violent — scarred the landscape from April 25-28, 2011, in what has been dubbed the Super Outbreak of 2011. There were 321 people killed during this period, with 316 of those deaths coming on April 27 alone.
On April 27, 15 violent tornadoes rated EF-4 or higher (including four EF-5s) struck the states of Mississippi, Alabama, Tennessee and Georgia. Alabama was the hardest hit, with 9 violent tornadoes touching down there, and 11 total crossing within its boundaries. The top two deadliest tornadoes in April since modern records began hit that day.
A tremendous longwave trough began to eject out of the West on the 25th as a frontrunning vort. max spawned a number of tornadoes across the South from Texas and to the east. This was only a sign of things to come as a very powerful low-amplitude vort. max poured in on a fast pattern still impacted by a waning La Niña.
It readied to unleash from the 26th through the 28th, with most of the fury directed at the 27th.
Though this several day sequence gets lumped together as one outbreak, it was — at least in my opinion — more accurately one outbreak on the 25th into the 26th followed by a larger outbreak that developed back over the southern Plains late on the 26th before rolling eastward through the 28th.
As (un)luck would have it, long-track supercells managed to find a number of areas with significant population on the 27th of April, all while dropping multiple fast-moving tornadoes that proved difficult to survive above ground. By the time it was all over, 31 deadly tornadoes had occurred, with 29 of them coming on the 27th.
The only other modern outbreak that compares is the similarly titled Super Outbreak of 1974. As tornado watchers know, it also came in April and impacted some of the same areas. That event actually had more killer tornadoes than the 2011 event, but none of the tornadoes killed quite on the scale of 2011’s most deadly. While the tornado count for April 2011 is a good deal higher, 1974 was also pre-Doppler radar days and it’s possible some tornadoes were missed.
Regardless of its exact rank in history, it was a once in a generation event that we all can hope skips the next generation.
Historic Tornado Outbreak April 27 – American Weather Forums (as it happened)
Historic Outbreak of April 27, 2011 – NWS Birmingham, AL (includes links to other NWS outbreak info)
Southeast US tornado outbreak of 27 April 2011 – CIMSS Satellite Blog
April 27th Outbreak: Meteorological Analysis – SevereStudios.com
Post Storm Discussion & Analysis of Apr. 27 outbreak – American Weather Forums
Mark Ellinwood contributed to this post.