Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 3:20 PM GMT en Abril 29, 2011
Rescuers sifting through the twisted wreckage of countless towns ravaged by Wednesday's historic tornado outbreak continue to uncover bodies today, and the death toll has swollen to over 300 this morning, and may be as high as 319. Hardest hit was Alabama, with at least 213 dead. Tennessee, Mississippi, Georgia, Arkansas, and Virginia are each reporting 11 - 34 deaths. NOAA's Storm Prediction Center logged 211 preliminary reports of tornadoes between 8am EDT Wednesday and 8am Thursday, and 346 reports for the full 4-day period of the outbreak, from April 25 - April 28. Twenty-two of these tornadoes were killer tornadoes; deaths occurred in six states. Damage surveys will take another week to complete, but preliminary surveys indicate that at least one of the tornadoes was an EF-5--the Smithville, Mississippi tornado, which hit at 3:44pm EDT on Wednesday. That tornado killed 13 people and destroyed 166 buildings, and reportedly sucked fire hydrants out of the ground. 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. Three other tornadoes from Wednesday's outbreak have been given preliminary EF-4 ratings, with winds of 166 - 200 mph. These include the Phil Campbell, AL tornado (26 deaths), the Ringgold, GA tornado (7 deaths), the Tanner, GA tornado (11 deaths), and the Apison, Tennessee tornado (13 deaths, and possibly the same tornado that hit Ringgold.) The violent tornado that ravaged Tuscaloosa and Birmingham, Alabama, killing at least 46 people and injuring 600, has not yet been given an official rating. I expect this tornado will be rated an EF-4 (possibly an EF-5.) This 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. The current record is the $3.5 billion price tag, in 2005 dollars, of the April 3 - 4, 1974 Super Outbreak . According wunderground's weather historian, Christopher C. Burt in his post The World's Deadliest Tornadoes, the death toll of 319 makes the April 25 - 28, 2011 tornado outbreak the fourth deadliest tornado outbreak in U.S. history, and the deadliest since 1936. It is the deadliest of the past 50 years, surpassing the April 3 - 4, 1974 Super Outbreak (315 killed) and the 1965 Palm Sunday tornado outbreak (256 killed.)
Figure 1. Still frame from an animation showing the height and extent of the rain columns associated with the thunderstorms that spawned Wednesday's tornadoes. This data, taken from NASA's TRMM satellite, showed that some of these violent storms reached incredible heights of almost 10.6 miles (17 km.) Image credit: NASA/SSAI, Hal Pierce
The 4-day total of preliminary tornado reports of 346 from this outbreak is close to the 323 preliminary tornado reports logged during the massive April 14 - 16 tornado outbreak. That outbreak has 155 confirmed tornadoes so far, making it the largest April tornado outbreak on record, and 3rd largest in history. The numbers from this week's outbreak may be even higher, giving April 2011 the 3rd and 4th largest tornado outbreaks in history, and the deadliest outbreak in 75 years. 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).
Figure 2. Storm chaser video from Reed Timmer and tornadovideos.net of four tornadoes that hit Alabama and Mississippi on Wednesday.
Figure 3. Storm chaser video of the tornado that moved through Philadelphia, Mississippi on Wednesday.
Unprecedented flooding predicted on Ohio and Mississippi Rivers
This week's storm system, in combination with heavy rains earlier this month, have pushed the Ohio River and Mississippi River to near-record levels near their confluence. The Ohio River at Cairo, Illinois is expected to crest at 60.5 feet on May 1. This would exceed 100-year flood stage, and be the highest flood in history, besting the 59.5' mark of 1937. Heavy rains of 10 - 15 inches have inundated the region over the past week. Additional rains of 1 - 3 inches are expected over the next five days.
Figure 4. Rainfall for the 7-day period ending at 8am EDT Thursday, April 28, 2011. Image credit: NOAA/AHPS.
Record 100+ year flood expected on Mississippi River
Snow melt from this winter's record snow pack across the Upper Mississippi River has formed a pulse of flood waters that is moving downstream. When this floodwater pulse moves south of Cairo, Illinois over the next two weeks, it will join with the record water flow coming out of the Ohio River, and create the highest flood heights ever recorded on the Mississippi, according to the latest forecasts from the National Weather Service. Along a 400-mile stretch of the Mississippi, from Cairo to Natchez, Mississippi the Mississippi is expected to experience the highest flood heights since records began 100 or more years ago, at 5 of the 10 gauges on the river along this stretch. The records are predicted to begin to fall on May 3 at New Madrid, and progress downstream to Natchez by May 20. Areas that are not protected by levees can expect extensive damage from the flooding, and it is possible that the Army Corps of Engineers will have to intentionally dynamite levees at Birds Point and New Madrid, Missouri to protect the town of Cairo from flooding. One unofficial estimate I saw on the Army Corps of Engineers web site put the cost of intentionally breaching the levees at Birds Point and New Madrid at $100 million dollars, due to damage to the croplands and structures in the flooded area. No levee has failed on the Lower Mississippi south of the Ohio River junction since 1950, and the Army Corp of Engineers has designed the levee system to contain a 500-year flood. This means that the Mississippi River flood of 2011--which will be somewhere between a 100-year and 200-year flood between Cairo and Natchez--is not likely to be a multi-billion-dollar disaster like the 1993 flood on the Upper Mississippi, where many levees failed.
The Mississippi River at New Madrid, MO, about 40 miles downstream of the confluence of the Mississippi and Ohio Rivers, is currently at 44.9', the 2nd highest flood in history. The river is predicted to crest on Tuesday very near the all-time record height of 48 feet. The NWS warns that at this height, "Large amounts of property damage can be expected. Evacuation of many homes and businesses becomes necessary." Previous record heights at this location:
(1) 48.00 ft on 02/03/1937
(2) 44.60 ft on 04/09/1913
(3) 43.60 ft on 04/04/1975
(4) 43.50 ft on 02/16/1950
(5) 42.94 ft on 03/17/1997
The timing of the floods crests will depend upon a complex mix a factors, including how much rain falls over the next month, the possible influence of southerly winds holding up the floodwater pulses, the potential opening of flood control structures and reduction of flows from flood control reservoirs, and potential levee failures. The Mississippi River is expected to crest at 17 feet at New Orleans on May 22, three feet below the top of the levees. This would likely require opening of the Bonnet Carre Spillway 28 miles upstream from New Orleans, to relieve pressure on the city's levees. Opening the spillway drains 250,000 cubic feet per second of flow into Lake Pontchartrain.
Helping out tornado victims
For those who want to lend a helping hand to those impacted by the widespread destruction this month's severe weather has brought, stop by the portlight.org blog.
Related post: Are tornadoes getting stronger and more frequent? The answer is--we don't know.
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