Some weather forecasters have suggested Tornado Alley, a swath through the Great Plains and Midwest that has seemed most prone to tornadoes, has shifted eastward to bring the killer tornadoes seen in the Chattanooga region this year.
But Greg Carbin, warning coordination meteorologist with the National Weather Service, says that is just too narrow a view.
Carbin says the alley really is a long L that for years has stretched into the Southeast.
But the tornadoes that mauled the Southeast six months ago were the super outbreak of all time.
Carbin said much more research is needed on the outbreak and the devastation it caused, but one thing is a pretty sure bet.
"It's likely to happen again," he said.
Blame it -- at least in part -- on a warming climate that will continue to evaporate more moisture off the ocean, prompting more extremes to impact the storms that already are bringing record floods and now possibly these record tornadoes to Tennessee, Georgia and Alabama.
David Gaffin, a senior forecaster for the National Weather Service in Morristown, Tenn., called the April 27 super tornado outbreak a subject of much future research.
"This was a very efficient event. It had 345 tornadoes -- more than double the previous record outbreak set in 1974," he told a symposium of weather experts a few months after the storms.
"Almost every storm was producing a tornado," he said. "It's the big event of our generation -- it's the big event of recorded history."
Daniel Weiss, senior fellow and the director of climate strategy at the Center for American Progress, a Washington, D.C.-based think tank, fears there are more records in the offing.
"This raises the question, 'Is this the new normal?'" he said last week, touting new statistics from the Federal Emergency Management Agency.
So far in 2011, there have been 86 FEMA extreme weather disaster declarations.
It's the second such record set in consecutive years.
Until 2010, when FEMA had to declare 81 disasters, the agency's average number of disaster declarations over the past 60 years was 33.
"Scientists have predicted these are the kinds of extreme events that would occur as global warming increases," he said. "Is the extreme weather of 2010 and 2011 the beginning of that?"
Weiss points out that in 2010 Nashville had a 1,000-year flood and this year -- just on the heels of the tornadoes, Memphis had its second-worst flood on record.
"In fact we've had so many record floods that we're changing the definition of what a 100-year flood is," he said.
Officials with the U.S. Geological Survey say the term "100-year flood" is used in an attempt to simplify the definition of a flood that statistically has a 1 percent chance of occurring in any given year. It is often misinterpreted to mean a flood that occurs about every 100 years.
The National Oceanic and Atmospheric Administration, the parent agency of the National Weather Service, has said that Earth's average temperature has risen by about 1.8 degrees in the past 100 years.
Weiss and scientists around the world say carbon pollution is causing a growing amount of heat in the earth's atmosphere, i.e., global warming. In turn, that warming is causing ocean temperatures to rise.
How can less than 2 degrees be so important?
Weiss, who just before the super tornado outbreak of all time helped write a report about 2010's extreme weather titled "The Year of Living Dangerously," said it's all about the oceans.
"It's the impact on the oceans that's driving a lot of the climate effects," Weiss said.
Earth's climate is both dynamic and fragile. As the oceans warm, they produce more water vapor, and when that happens there are more severe storms because there's more moisture in the atmosphere, he said.
"Because we have not brought carbon pollution under control, the weather events of 2010 will continue to revisit us -- with a vengeance," he wrote in the "The Year of Living Dangerously."
Vehicle exhausts and power plant pollution are largely the culprits in two major countries: China and the United States -- in that order, according to climate reports.
Weiss said the U.S. has made progress on car exhaust but still has a long way to go on power plant pollution.
Two proposals seeking change have not gotten to the president's desk, he said. On party line votes, the House of Representatives earlier this year defeated an amendment that says climate change is occurring. The amendment was offered by U.S. Rep. Henry Waxman, D-Calif., and it would have accepted the scientific findings of the Environmental Protection Agency stating the change is caused largely by human activities and poses significant risks for public health and welfare.
Another bill was a basic proposal to address the problem. The market study done for the bill found that carrying out the proposal would cost American households about $25 a year.
Weiss and others have warned that time for action is running out.
To add insult to injury, Weiss said the House voted to defund federal science programs that gather and analyze the data essential to understand changes in global weather patterns and other climate impacts.
"But all this denial cannot make this threat disappear," Weiss' report states.
Forecasters are in full agreement that climate change is contributing to record rains and floods, but generally they are still iffy on what impact the warming oceans have on tornadoes. More goes into making tornadoes, Carbin said, than just warm air and moisture. There also has to be a good dose of cold air in the upper atmosphere to create wind shear.
But he said researchers have made good progress on predicting the weather patterns that make tornadoes likely.
And that's what forecasters used in the days leading up to April 27.
The bad weather alerts they issued likely helped keep the record outbreak's death toll -- 547 --below the all-time tornado death record. That still is held by the March 18, 1925, Tri-State Tornado that claimed 695 lives in Missouri, Illinois and Indiana -- long before warnings were available.
"There have been 14 outbreaks over 135 years that killed 200 or more people," Carbin said, adding that clusters of deaths prior to 1950 happened largely because the tornadoes came with little notice.
"Since the 1950s, we can get the word out better," he said.
But that warning still comes down to a matter of minutes -- on average, almost 14 minutes. In the late 1970s, the average was three minutes.
"Science is just not at a point yet where I can give you a three-hour window that a tornado is coming," Carbin said.
In April, two days before the record tornado outbreak blasted across Dixie, the National Weather Service was calling emergency responders and posting weather bulletins for the public and the media.
In Chattanooga, reporters from several media outlets were invited to the 911 Center to hear Weather Service assessments of a dangerous weather pattern likely to spawn supercell thunderstorms and twisters.
"That's a testimony to the progress we've made in forecasting," Carbin said. "But the devil is always in the details. We can do it on a large scale -- like states. But we can't get it down much from there yet."
Aside from forecasting, there are needs for other tornado and extreme weather research.
Carbin said tornadoes in recent years have caused more fatalities in the South than in the Midwest.
The Southeast is more vulnerable because of less stringent construction codes, and the population is more dense, he said.
In the end, he said, there's no such thing as a 100 percent certainty about tornadoes until an event occurs.
"That's the nature of nature. It's going to hide its secrets until it does what it will do," Carbin said.
Watch Channel 3 or visit WRCB-TV.com today at 5 p.m. and 6 p.m. for inspiring stories of life after the storm. Chief Meteorologist Paul Barys meets the people who were watching the Storm Alert 3 Team on April 27.