Anniversary of Deadly, Historic Tornado Outbreak

Damage in Tuscaloosa, AL in the aftermath of the April 27th, 2011 F4 Tornado

One year ago today marks the deadly anniversary of one of the most prolific and deadliest tornado outbreaks in U.S. history. “Historic, record-breaking, devastating, heart-breaking…” These are just some a few of the words being used to describe the outbreak of tornadoes that swept apart parts of the Southeast.

Previous to last year, the “Super Outbreak” in 1974 was the benchmark for tornado outbreaks in the US. In 1974, there were 148 tornadoes over 13 states. 330 people were killed over a 16 hour period. Last years outbreak which started on the 25th of April, and peaked during the afternoon and evening of the 27th produced more than 200 tornadoes. 316 people lost their lives, and damage exceeded 4 billion dollars.

As a meteorologist who has been studying tornadoes for a long time, it was frightening to think that in this modern-day of advanced tornado detection and warnings that we could see that many people parish in the storms.

A NOAA study that looked at the outbreak in the days and weeks after found that “All tornado fatalities occurred within the boundaries of tornado watches and were preceded
by tornado warnings.” They also found that the average lead time was over 22 minutes, which meant people on average should have known 22 minutes in advance that a deadly tornado was on the way. Back in 1974 many of the deadly tornadoes went undetected or had lead times of 5 minutes or less. So why did we have such a high death toll?

The answer was in the violent nature of many of the tornadoes a year ago, and the populated areas they hit.  Tornado damage and intensity are ranked on a scale called the Enhanced Fujita Scale.  The scale ranges from F0 (weakest) to F5 (catastrophic). Winds in an F5 reach over 200 mph. You can go several years without seeing an F5 tornado anywhere on the globe. There have only been 58 F5 tornadoes observed since 1950. On April 27th of last year there were 4 on one day! By definition an F5 tornado will wipe a house completely off its foundation, so unless you are underground an F5 tornado is not survivable. There were also 11 F4 tornadoes on that day (the average is one a year). These are also considered violent tornadoes. The other main factor making last year such a deadly day was the tornadoes were not in the typical “tornado alley”, but were further east and south in what is being called “Dixie alley”. The bottom line was there were a lot more people in the path of the storms. Tornadoes that day moved through the populated areas of Tuscaloosa, where the University of Alabama is located and the same tornado stayed on the ground through parts of Birmingham.  To complicate matters even further there are few storm cellars or basements like there are in other parts of the country.

The historic season continued through much of April and May, producing a record 758 tornadoes in April, and a record 542 in May including the deadly Joplin tornado on May 22, killing 157.


By CNN Senior Meteorologist Dave Hennen and CNN Meteorologist Sarah Dillingham

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