Two EF-5 tornadoes confirmed from last week's outbreak; record Ohio River flood

Damage surveys and the hunt for missing victims continues today in the areas devastated by last week's historic tornado outbreak. With the death toll in the 340 - 350 range, the April 25 - 28 tornado outbreak has surpassed the April 3 - 4, 1974 Super Outbreak (315 killed) as the deadliest U.S. tornado outbreak of the past 50 years. Hardest hit was Alabama, with 249 deaths; Tennessee and Mississippi had 34 deaths each, and deaths were also reported in Arkansas, Georgia, Virginia, Louisiana, and Ontario, Canada. Twenty-eight separate tornadoes killed people. According wunderground's weather historian, Christopher C. Burt, in his post The World's Deadliest Tornadoes, only the death toll of the great Tri-State tornado outbreak of 1925 (747 killed) and the 1936 Tupelo-Gainsville tornado outbreak (454 killed) were greater. These outbreaks both occurred during an era before Doppler radar and tornado warnings. Had last week's outbreak occurred back in those days, I expect the death toll would have been in the thousands. The National Weather Service provided warning times of 15 - 30 minutes for all of last week's killer storms, allowing time for most people to get to safe shelters.


Figure 1. MODIS satellite image from NASA's Aqua satellite taken on Friday, April 29, 2011, showing the damage paths of three of Wednesday's tornadoes in Alabama.


Figure 2. Damage paths of Wednesday's tornadoes as compiled by the National Weather Service office in Birmingham, Alabama.

Damage surveys will continue for another week, so it is uncertain exactly how many tornadoes were spawned in last week's outbreak. The confirmed count is already at 146, which would make it the 4th largest tornado outbreak in history. The total is likely to surpass the 155 confirmed tornadoes logged during the April 14 - 16, 2011 tornado outbreak. According to a list of tornado outbreaks maintained by Wikipedia, only two other tornado outbreaks have had as many as 150 twisters--the May 2004 outbreak (385), and the May 2003 outbreak (401). So, remarkably, two of the top four outbreaks in history occurred within two weeks of each other. In addition, the period from 8am April 27 - 8am April 28 during last week's outbreak has a good chance of breaking the record for most tornadoes in a 24-hour period, which is currently 148 (set in the April 3 - 4, 1974 Super Outbreak.)

Two EF-5 tornadoes confirmed
Damage surveys have confirmed that last week's April 25 - 28 outbreak spawned at least eleven violent EF-4 tornadoes (winds 166 - 200 mph) and two EF-5 tornadoes (winds greater than 200 mph.) This is only the 5th time since tornado ratings began in 1950 that two top-end tornadoes have occurred on the same day. The last time was on March 13, 1990 in Kansas. An EF-5 with 205 mph winds hit Smithville, Mississippi at 3:44pm EDT on Wednesday. The tornado's path was only 3 miles long, but was 1/2 miles wide and did extreme damage. Fifteen were killed, 40 injured, and 166 buildings destroyed. Some well-built modern 2-story homes that were bolted to their foundations were completely destroyed, leaving only the foundation. This type of damage is characteristic of an EF-5 tornado with 205 mph winds. The Smithville tornado is the first EF-5 tornado in Mississippi since the Candlestick Park tornado of March 3, 1966. The other EF-5 tornado of the day, the Hackleburg tornado, touched down in Northwest Alabama in Marion County at 3pm CDT, and devastated the towns of Phil Campbell and Hackleburg. This tornado killed at least 25 people. Meteorologist Gary Dobbs, with WAAY-TV since 1984, spotted this tornado from his car and was unable to get to his storm shelter. While his house was destroyed around him, Dobbs was thrown 40 feet from the house. The door of the storm shelter blew off, and none of the friends therein were seriously injured. Dobbs required hospitalization. One other tornado that may get an EF-5 rating is the violent Tuscaloosa/Birmingham tornado, which killed at least 66 people and injured over 1000. It was the deadliest tornado in the U.S. since 1955, when 80 people died in Udall, Kansas. This tornado had a path length of 80.3 miles, and has been preliminarily rated at high-end EF-4 with 190 mph winds. The Tuscaloosa-Birmingham tornado is likely to be the most expensive tornado of all-time, and damage from the April 25 - 28 outbreak is likely rank as the most expensive tornado outbreak in history. Insured damages have been rated at $2 - $5 billion, and uninsured losses will be several billion more. The previous most expensive tornado outbreak in history was the $3.5 billion price tag, in 2005 dollars, of the April 3 - 4, 1974 Super Outbreak .


Figure 3. Radar reflectivity image of the Hackleburg, Alabama tornado of April 27, 2011, a few minutes after it devastated the town of Hackleburg, Alabama (white cross at center of image.) The Hackleburg tornado was rated an EF-5 with greater than 200 mph winds.


Figure 4. Remarkable video of the tornado that hit Tuscaloosa, Alabama. Beginning at about 2:30 into the video, one can see the ominous mini-vorticies and cloud of debris that encircled the tornado.

Unprecedented flooding on Ohio River
Last week's storm system, in combination with heavy rains earlier this month and over past 24 hours, pushed the Ohio River at Cairo, Illinois to 60.6 feet at 1am CDT May 1. This is the highest flood in history, besting the 59.5' mark of 1937. Additional heavy rains of 2 - 4 inches are expected over the next five days, and the river is not expected to crest until Wednesday, at a height of 61.5 feet. As the record flood waters from the Ohio River pour into the Mississippi and are joined by melt water from the this winter's record snow pack over the Upper Mississippi, all-time flood heights are likely to be exceeded at many points along a 400-mile stretch of the Mississippi below its confluence with the Ohio. I'll have a more detailed look in my next post.

Jeff Masters