Alabama Tornado Outbreak 2011

Here at Three Scale, we focus on a number of topics that use GIS. One topic in particular for this blog post is on weather. Back in April and May of this year, we did some research and created a GeoPDF from a recent weather event in the Southern United States.

On Wednesday April 27th, 2011, a severe weather event occurred in the South from Mississippi to Georgia. The severe weather event helped manifest a large tornado outbreak in northern and central Alabama. A low-pressure system cold front moved from the Southern Great Plains towards the South over the course of several days, allowing the system to pick up moisture from the Gulf of Mexico to help it gain strength. Coupled with warm air in front of and cold air behind the low-pressure system, the storm system had the characteristics necessary to produce tornadoes in this unstable air mass. In total, over 292 tornadoes touched down on April 27th, 2011, a number far greater than the Super Outbreak on April 3rd, 1974. The April 27th outbreak killed 339 people over the course of several days, a number not seen since a previous tornado outbreak in 1936. Many of these deaths came from people living either in mobile homes or homes that did not have a basement.

In the early morning hours of April 27th, 2011, several tornadoes touched down between the hours of 3am and 6am before dissipating until 3pm when the conditions were favorable again for storm regeneration. The National Weather Service’s Storm Prediction Center issued a high risk for parts of eastern Mississippi, southern Tennessee, western Georgia, and north and central Alabama for April 27th. A high risk from the Storm Prediction Center means that on a given day, a storm passing through a certain area in the United States has a favorable chance of 30% or greater of producing at least one tornado (NWS). Their predictions would later be proven correct.

Of the 292 tornadoes that touched down on April 27th, 2011, 53 were in the state of Alabama. Out of that 53, four were classified as an EF-5 on the Enhanced Fujita Scale, an event that had not occurred since 1990 when two F5 twisters (on the former Fujita Scale) touched down (NWS). One tornado in particular, an EF-4, was a mile wide in diameter causing extensive damage to homes and businesses just south of the central business district in Tuscaloosa, Alabama, narrowly missing the University of Alabama as it moved eastward towards Birmingham killing 65 people (NWS). Another tornado, also classified as an EF-4, was caught live on a television tower camera in Cullman, Alabama, about 51 miles north of Birmingham during a weather broadcast of the tornado outbreak. This tornado caused major damage to several buildings in downtown Cullman and killed six people (NWS). The results from the tornado outbreak forced the President to declare a federal emergency declaration to allow more resources for search and rescue of missing people (Francis). Damages to the storm event may total from $2.45 billion to $4.2 billion in the state of Alabama alone (Thomas).

Not only did this system produce a large amount of tornadoes, but also hail and high winds gusting up to 65 mph or greater. The storm system also dumped heavy rain in the South, Midwest, and Great Plains causing the Ohio and Mississippi Rivers to become swollen and flood large swaths of farmland threatening cities over the course of several weeks. The South was not the only area to be affected on that day, as a number of tornadoes and high winds were also reported in the Mid-Atlantic States of Virginia, Maryland, Pennsylvania, and New York, though the intensity of the storms was less compared to the South.

Click map to view larger image.

Click map to view larger image.

Super Outbreak2

If you look on the radar animation on the GeoPDF, you can see the line of storms that passed through during the early morning hours of April 27th, 2011 and then regenerating again by the afternoon spawning the large tornado outbreak in North and Central Alabama. The people from Weather Underground were graciously helpful in allowing us to use their weather radar for the GeoPDF when we contacted them about using their radar animation from April 27th over a 24 hour period. On the bottom left corner shows a map of where tornadoes, hail, and high winds 65mph or greater where recorded on April 27th. We were able to gather the data from NWS’s Storm Prediction Center site. On the bottom right corner shows an image map of the Storm Prediction Center’s risk for severe weather on April 27th.

The April 27th, 2011 tornado outbreak not only affected Alabama, other states up along the East Coast were affected too. There was the question that global warming played a factor in this outbreak contributing to the high death toll due to the intensity of the tornadoes. However, the dearth of basements in the South did play a role to the high death toll and enforcing regulations such as adding basements and/or ban on mobile homes on future housing stock could mitigate future fatalities from tornadoes in the South (Revkin). The South has one of the highest concentrations of manufactured homes which can be destroyed easily by EF-1 tornado or greater. The tornado outbreak also confirmed once again, the South is not immune to twisters as the intensity of the twisters matches those in Tornado Alley which include Texas, Oklahoma, and Kansas. Ohio has seen its share of twisters before during the Super Outbreak in 1974. Time and weather will tell whether or not Ohio is due for another major twister outbreak.
1. National Weather Service. “Storm Prediction Center Storm Reports for 4/27/2011” April 27, 2011. <>.
2. Revkin, Andrew C. “In Tornado Zones, Seeking Shelter From the Storm” New York Times. May 3, 2011. <>.
3. National Weather Service. “April Severe Weather Events Set New Tornado Records for Alabama” NOAA. <>.
4. National Weather Service. “Historic Tornado Outbreak April 27, 2011” NOAA. April 28, 2011. n=event_04272011>. <>.
5. National Weather Service. “Cullman(AL)/Morgan(AL)/Marshall(AL) EF-4 Tornado – Lewis Smith Lake (near CR 310) near to Union Grove” NOAA. <>.
6. Francis, Enjoli, et al. “Storms, Tornadoes Leaves Dozens Dead in Alabama, Mississippi, Georgia, and Tennessee” April 27, 2011. <>.
7. Thomas, Spencer. “Alabama Tornado Outbreak May be State’s Costliest Natural Disaster” The Birmingham News. May 16, 2011. <>.