Rare power: Perfect combination of ingredients led to storm's intensity
by Bob Davis and Lisa Davis
Star staff editors
May 01, 2011 | 8586 views |  0 comments | 21 21 recommendations | email to a friend | print
Damage is shown in the Webster's Chapel area in this aerial shot. (Anniston Star photo by Trent Penny)
Damage is shown in the Webster's Chapel area in this aerial shot. (Anniston Star photo by Trent Penny)
slideshow
The cold front swept down over the plains, pushing cool, dry air down from the Rocky Mountains. The Southern states lay under a blanket of warm, steamy air blowing in from the Gulf of Mexico. Warmer than average this year. Like octane gas waiting to get lit.

The dense, cold air smashed into the warm air, barreling underneath it like a wedge splitting a log. Strong winds from the south shoved the warm air up, up, up, where it ran headlong into the jet stream, blowing at 150 mph. Stronger than normal this year. At 20,000 feet, the wind was blowing in another direction, to the southwest. It didn’t take much for the storm to start spinning.

The storm fed on the warm air it was sucking in from below, feasting on it. It exploded upward, 50,000 feet into the atmosphere. As it got higher, it spun faster. And the strong winds in the upper atmosphere began to push the storm, and push, and push, like they would never let up.

It had been gathering for a week. On Tuesday, it caused an outbreak of tornadoes in northeast Texas, across northeast Louisiana, southern Arkansas, northern Mississippi.

In Van Zandt County, Texas, more than 100 homes were damaged. “Just devastation,” resident James Hoskins told a Dallas TV station.

In Monroe, La., the storm dumped more than six inches of rain. Authorities suspect two Louisiana residents drowned because of flooding.

In Choctaw County, Miss., at a national park off the Natchez Trace, 40-year-old Wade Sharp, a police officer in Covington, La., was camping with his 9-year-old daughter. Before sunrise Wednesday, a large tree pushed over by strong winds landed on Sharp’s tent, killing him. His daughter survived, as did a building no more than 50 feet away.

In Kemper County, Miss., Florrie Green and her sister, Maxine McDonald, along with their sister-in-law, Johnnie Green, were killed when their mobile home was struck by a storm; all three women were in their 80s.

“They were thrown into those pines over there,” a relative told the Associated Press, pointing to a wooded area. “They had to go look for their bodies.”

The death toll in Mississippi was more than 30.

ALL THE INGREDIENTS

A tornado needs two things to form: instability (cold air vs. warm air) and wind shear (strong winds aloft that change speed or direction quickly).

“Wednesday was all the ingredients we learn about in college. It was like a textbook outbreak of violent tornados,” said Bob Smerbeck, a senior meteorologist with Accuweather.com. “You need the cool air to clash with the warm air, you need the strong jet stream, and you need some twisting as well.”

If there’s instability without wind shear — if the winds all line up in the same direction — you just get a solid line of thunderstorms. But if wind shear twists the storm apart into individual cells, “they take on their own environment, they feed off the environment, they can become stronger,” said Smerbeck. “By themselves, they can spin freely.”

The United States is the most tornado-prone part of the world, explained Jeff Masters, director of meteorology at Weather Underground, in part because it sits precisely between two of the ingredients needed: cold air from Canada, warm air from the Gulf of Mexico.

But this outbreak? “It was a rare kind of perfect storm,” Masters said. “This only happens once every 30 years in the U.S.”

THE FIRST WAVE

Before sunrise Wednesday morning, the narrators of Alabama’s severe storms — the Birmingham market TV weather forecasters — were on the air.

On Birmingham’s ABC affiliate, Jason Simpson told viewers that a storm moving through the pre-dawn darkness in Tuscaloosa might show all the signs of a tornado.

Peggy Brown of Alexandria awoke at 6:30 a.m. to the “worst noise you’ve ever heard.” The winds knocked down trees and damaged homes across western Calhoun County. “The wind was shaking the house,” Brown said. “I could feel it.”

Authorities reported that two Pell City residents died as a result of the early-morning winds, which were estimated to be up to 100 mph. In Anniston, trees were downed all over town.

By 9 a.m., Alabama Power was reporting more than a quarter-million homes were without electricity.

Social media outlets Facebook and Twitter lit up by mid-morning. One poster summed up the storm, noting, “Pell City got messed up.” On Facebook, Ray Ray wrote, “Everyone please keep up with this weather today. They are already saying the weather today could be just like it was in 1974 when the big tornado outbreak hit Alabama or worse. BE SAFE EVERYONE.”

Students had barely arrived at most schools in Calhoun County before they were told that they would be going home early.

The weather narrators told us to batten down. Something much worse was coming.

James Spann, Alabama’s go-to TV meteorologist, would remain on the air hour after hour, delivering bad news.

NAMELESS FURY

We don’t name tornados the way we name hurricanes. We remember tornados in the language of tombstones.

St. Louis, 1896.

Moore, Oklahoma, 1999.

Goshen.

DANGEROUS,

LIFE-THREATENING


Just after 2:30 p.m., the National Weather Service reported a tornado moving 50 mph had been spotted eight miles southwest of Cullman. “This is a dangerous and life-threatening situation.”

Birmingham TV station cameras mounted atop tall buildings in Cullman zoomed in on the rapidly approaching funnel cloud. “This thing is kicking up all kinds of stuff here,” said Fox 6 TV meteorologist James-Paul Dice, referring to swirling debris caught up in the roaring wind.

By 3 p.m., the National Weather Service warned counties in east-central Mississippi that more tornados were likely.

In Newton County, Miss., at 2:54 p.m., a supercell thunderstorm spawned one of several tornados that would cross the border into Alabama.

This one was aimed straight at Tuscaloosa.

It would chew its way northeast for more than 80 miles.

By 5:09 p.m., it was tearing across McFarland Boulevard.

In a video that went viral, Chris England of the University of Alabama’s Crimson Tide Production Team kept a camera trained on the monster twister. For two minutes, the only narration is England’s panicked breathing, as the mile-wide tornado rips apart several city blocks.

“Apparently 15th Street and McFarland are unrecognizable. My friend’s car is crushed, but they are ok,” wrote sweetTlibrarian on Twitter. “I could just cry for Tuscaloosa.”

The tornado lifted just before it would have crossed Highway 79, wrote Bill Murray on ABC 33/40’s weather blog. If it hadn’t lifted, “it likely would have struck the campus directly.”

MEASURING THE STORM

Was it an EF4? An EF5? The National Weather Service couldn’t immediately classify the Tuscaloosa tornado because the F scale is a measurement of damage, not wind speed. An EF5 could move across an open pasture but, without any structures to damage, not be measurable.

The “F” is the tornado scale stands for “Fujita.” Dr. T. Theodore Fujita of the University of Chicago devised the scale to classify U.S. tornados in 1971. He divided them into six categories, from F0-F5, depending on how much havoc they wreaked.

Soon, scientists started taking the Fujita scale and using it to estimate the wind speeds within a tornado.

The F scale was tweaked in the late 1990s, and weather scientists now use the EF-scale, the Enhanced Fujita scale. An EF-0 tornado was probably spinning at 65-85 mph, an EF-3 at 136-165 mph. Anything over 200 mph is a 5.

“It’s very rare to actually measure winds in a tornado — maybe one in 1,000,” said Masters. To get an actual measurement requires a mobile Doppler radar mounted on a truck. “They park the truck and point it right at the tornado,” Masters said. But even that doesn’t measure the wind speed at the surface. They have to aim the radar about 100 feet above the ground.

The fastest tornado ever recorded was 302 mph, during the Oklahoma outbreak of 1999.

FALLING DEBRIS

The first tangible sign of trouble was debris randomly falling from the sky. The personal belongings from Tuscaloosa homes and businesses caught up in the whirlwind were landing in front of the storm as it moved through Jefferson County.

In Birmingham, the tornado filled the screens of cameras atop Red Mountain. “Extreme damage has been reported,” said the anchor.

The tornado was at its widest point when it crossed Interstate 65 north of Birmingham — one-and-a-half miles wide.

The widest tornado ever recorded was two-and-a-half miles wide, measured during the Oklahoma outbreak of 1999. It was the brother of the tornado that clocked in at 302 mph.

BLOWN AWAY

After the tornado left Birmingham, it lifted back up into the swirling storm clouds.

But it wasn’t gone for good. As the sun began to set, it regrouped, reenergized, changed character — and took aim at Calhoun County.

At 6:58 p.m., The Star tweeted, “Tornado warning. If you are in Ohatchee or other parts of northwest Calhoun County, seek shelter NOW.”

By 7:15 p.m., Ohatchee and surrounding areas were catching the worst of the storm. Houses near the Coosa River were blown away by strong winds.

Lisa Spinks caught the approaching twister on video. “I would have to estimate that the foot of the tornado was only about two football fields away from us,” she wrote on YouTube. “Our vehicle was being rocked and pulled with only the mere edge of the storm.”

By the time the tornado exited Calhoun County around 8 p.m., it had claimed at least nine lives and demolished untold numbers of homes.

That part of the story will continue to be told for generations.

‘IT’S RIDICULOUS’

By Saturday afternoon, the map of Alabama on the National Weather Service’s Birmingham website was slashed with parallel diagonal lines — pink, red, orange, lime green, black — marking the paths of at least 15 tornados. Five of the tracks were confirmed as EF-3 or stronger.

The number of tornados in Wednesday’s outbreak across seven states is 211 by NOAA’s preliminary estimate. That comes on the heels of the 243 tornados in the April 14-16 outbreak.

“It’s really rare to have this combination of effects stay in place for so long,” Masters said. Outbreaks of more than 150 tornados at one time are rare. “To have two in the same month of the same year … it’s ridiculous.”

In an average April, the country suffers through 160 tornados. This year, it was more than 600.

GETTING AHEAD OF THE STORM

On April 3-4, 1974, 148 tornados touched down in 13 Southern states. The super outbreak lasted for 16 hours. It killed 330 people. Its path of destruction stretched for more than 2,500 miles.

On April 3-4, 1974, all that weather forecasters could see on their radar scopes were green blobs.

Masters shudders to think what the death toll of last week’s tornados would have been without modern monitoring and warning systems. But even those advances aren’t enough.

“We don’t really understand how tornados form,” Masters admitted. “We need to get that down before we can get better warnings.”

Now, the average lead time on a tornado warning is only 13 minutes. And 70 percent of tornado warnings turn out to be false alarms.

The most ambitious research project yet into the genesis of tornados took place last spring, a $10 million federal initiative called Vortex 2. More than 100 scientists and 40 vehicles chased storms on the plains, circling the entire fleet around tornados and pointing scientific instruments into the maelstrom.

“Eventually, we’re going to start launching remote probes into tornados,” Masters said. Computer modeling of storms should also continue to advance. “In a decade, say, we’ll be able to increase warning times by another 50 percent — I’m hoping.”

To try to predict how climate change will affect future tornado activity, Masters said, you need to look at the two ingredients needed to form a tornado: instability and wind shear.

“We suspect that in a future climate, the jet stream will get weaker. There will be less energy available to make the air spin. That would argue that we might see a decrease in tornado activity,” said Masters.

“The flip side of that is, in a warmer world, we expect the atmosphere to be more unstable. More water can evaporate into a warmer atmosphere, so you will have more moisture in the air, more warm air down near the surface.

“The two effects are going to compete with each other. It’s uncertain which one will come out on top.”

MORNING AFTER

After ravaging northern Calhoun County, the tornado passed into Georgia. The supercell storm that had spawned it and other violent twisters finally dissipated in Macon County, N.C., at 10:18 p.m. The supercell had existed for seven hours and 24 minutes and had traveled 380 miles, according to the National Weather Service.

By 10 p.m. Wednesday, social media was abuzz with Calhoun County churches and others organizing volunteers for relief work.

By 9 a.m. Thursday, Kent Mattox, pastor of Oxford’s Word Alive church, tweeted, “We are on the ground in Ohatchee Alabama delivering food and water. Devastation everywhere.”

By Thursday afternoon, the jet stream had pushed the remnants of the storm east and northeast. The cold front was along the East Coast. What was left of the storm was in Quebec.

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