In weather history, 11 years ago one of the deadliest and costliest tornado outbreaks in U.S. history happened over a three-day span. The most active day of the Super Outbreak of 2011 was April 27th, when more than 60 tornadoes in Alabama killed 250 people and injured thousands.
The worst of the outbreak unfolded April 27th and lasted into April 28th. April 27′s 316 fatalities were the most tornado-related deaths in the United States in a single day since the “Tri-State” outbreak on March 18, 1925.
The storm path exceeded 3,200 miles, the most recorded for a single outbreak. States affected: Alabama, Arkansas, Florida, Georgia, Indiana, Maryland, Mississippi, Missouri, New York, North Carolina, Ohio, South Carolina, Tennessee, Virginia and West Virginia. Five southeastern states accounted for more than 200 of the 360 tornados.
Also, 27 April was the first time the Mississippi would experience a pair of F/EF5 tornadoes on the same day.
Most of the 324 national deaths (253) happened in Alabama. It was the deadliest tornado outbreak since the worst on record in 1974. The event set a record for the most tornadoes in one storm system (360) and the most during a single day (216).
Tuscaloosa, AL was one of the hardest-hit areas. A tornado with a diameter of almost 1 mile (1.6 km) and wind speeds of approximately 200 miles (320 km) per hour devastated residential areas to the tune of $2.45 billion. According to the Christian Science Monitor, “The Tuscaloosa twister alone may register as the most powerful long-track tornado in US history.”
The king of a series of massive long-track tornadoes that clobbered the South this week may have traveled in excess of 220 miles across Alabama, Georgia, and Tennessee, carrying wind speeds in excess of 200 miles per hour, all of which could make it the most powerful tornado ever recorded in the US.
The only rival so far is the 1925 “Tri-State Tornado” that ripped through the upper Midwest on a 219 mile track, killing over 700 people.
Less than a month later, on 22 May 2011, a tornado in Joplin, MO caused $2.8 billion in damage.
In 2015, researchers published a report in Geophysical Research Letters that showed how “smoke particles in the atmosphere further enhanced conditions already favorable for intense tornado formation.”
At the time of the outbreak, large amounts of smoke spewed by agricultural fires drifted across the Gulf of Mexico from Central America and into the United States. In the spring, Central American farmers often deliberately set fire to their fields in order to clear out old crops and fertilize the soil for planting. To see whether the smoke played a role in the record-setting U.S. tornado outbreak, Saide and colleagues assembled a computer simulation of the region. In their reconstruction, the researchers could compare atmospheric conditions with and without the smoke.
David Glenn, a Chattanooga, TN meteorologist, reflected on that day:
Meteorologists can get a gauge of the “potential” energy within a developing storm system by looking at various computer model indices. One such equation or index is called the SWEAT index which stands for “Severe Weather Threat” index. It takes into account the stability of the atmosphere and the wind profile. A SWEAT index of over 400 means that supercell storms are likely with some that could produce strong tornadoes. The projected SWEAT index for April 27th was 527! Two different computer model runs on April 26th yielded totals above 500. I then emailed my boss, Tom Henderson, to give him a brief on my thoughts for the next day. I told him exactly what I told my wife…“I have never seen anything like this set up before locally and it could be very bad”. I closed the email with this quote…”I hope I am wrong”. If there was ever a forecast when I wanted to be wrong, it was this one.
Weather fatalities make forecasting essential
Improved weather forecasting has reduced the annual death toll associated with tornadoes.
On 27 April 1898, the Weather Bureau launched its first weather kite from Topeka, Kansas. The kites were large (8 feet long x 7 feet wide x 3 feet high) and the kite wire could hold up to seven kites. In 1894, William Eddy used five kites to make the first temperature observations aloft.
Congress, at the request of President Benjamin Harrison, had transferred “the meteorological responsibilities of the Signal Service to the newly-created U.S. Weather Bureau in the Department of Agriculture” on 01 October 1890.
During the 2011 crisis, “the National Weather Service maintained an average warning lead time of 24 minutes, allowing many people to escape or prepare for the disaster.”