Recipe for a disaster: How this week's tornadoes formed
In Alabama, the hardest-hit state, the storms destroyed hundreds of businesses and homes, such as this one in Tuscaloosa.
April 29th, 2011
01:54 PM ET

Recipe for a disaster: How this week's tornadoes formed

A wave of storms swept through the South this week, laden with tornadoes that killed at least 300 people and left a multistate trail of destruction.

As authorities continue to assess the damage, recover bodies and restore power to thousands of homes and businesses in the storm zone, weather experts have many questions about the confluence of factors that formed such a violent weather system.

Did a perfect storm of sociological, meteorological and geographical events combine to create the second-deadliest tornado outbreak in the nation's history since 1950? The University Corporation for Atmospheric Research's Bob Henson, who recently wrote about the recipe for the storms, said it seems that way, but perfection is relative.

"You never know what’s perfect, because there may be another storm that’s even more perfect. Many say the 1974 super outbreak was the ultimate event," he said.

In 1974, a super outbreak of tornadoes churned through 13 states, killing hundreds of people.

One thing is certain: Way before Wednesday's storms came, forecasters saw the ingredients for trouble in the skies.

Weather forecasters had "very, very strong signals actually about five days out indicating a significant weather outbreak," Greg Carbin, warning coordination meteorologist at NOAA's Storm Prediction Center, told CNN on Friday.

But "saying a significant weather outbreak is coming is quite different from saying a massive tornado will move through Tuscaloosa at 5 p.m.," Carbin said. "So knowing the big picture is pretty good, but you don’t know the specifics; you only know really after the thunderstorm begins to form."

Around midday Wednesday in Mississippi, funnel cloud reports began.

“Tornadoes typically form from what are called super-celled storms,” Greg McFarquhar, a professor in the Atmospheric Sciences Department at the University of Illinois, told CNN on Friday. “You need a number of different ingredients. One is warm, humid air toward the surface. You need some sort of trigger that will start that air rising, that is associated with a cold front, and then a third ingredient is instability in the atmosphere,” he said.

“When a parcel of air starts to rise, if it’s warmer than the surrounding air, it’s going to be less dense than the surrounding air, and it will continue to rise,”  McFarquhar said.

Throughout the day Wednesday, the National Weather Service issued tornado watches - a "particularly dangerous situation" - for parts of Mississippi, Alabama, Tennessee, South Carolina and Georgia.

Other agencies were issuing advisories as well. NOAA’s Storm Prediction Center in Norman, Oklahoma, issued its highest threat warning - “high risk” - for parts of the South. Shortly after, the prediction center issued red-colored headlines on its advisories, noting the likelihood of “destructive tornadoes … large hail up to 4 inches in diameter … and dangerous lightning.”

Another crucial ingredient was wind shear: volatility in wind speed and direction.

"Storms happen all the time," Carbin said, "but for those storms to last, you need wind shear.  If not, it will actually self-destruct. Wind shear will allow the storm to form a very efficient chimney, so to speak," he said.

On top of it all was a fast-moving storm system that raked parts of six states.

"It first showed up in Mississippi," Carbin said, "and at the same time, it wasn’t just one storm, it was five, 10, 15 erupting one after another in a 30-minute span. We know that. What we don't know is how to provide a specific pinpoint forecast of a violent tornado. That's still out of reach."

Armed with data from the National Oceanic and Atmospheric Administration and the National Weather Service, meteorologists in the affected regions went live with coverage of the storms’ path. But there was a major problem in getting the word out.

High winds associated with the storm had already caused power outages in several areas of the tornado zone as tree limbs snapped and power lines fell. Henson said he heard anecdotally that some NOAA weather radio transmitters were down as well, adding to the confusion.

Among the series of storms was at least one, in Smithville, Mississippi, that was an EF5. The National Weather Service in Memphis, Tennessee, said Friday the twister was Mississippi's first EF5 in more than 40 years.

An EF twister generates winds of more than 200 mph, according to the National Oceanic and Atmospheric Administration.

Soon afterward, witnesses reported tornado touchdowns in parts of Alabama.

In Alabama, where most of the damage was done, media and residents are calling another twister, captured on video, simply a "monster."

But how could so many people perish in an event that was forecast?

"Sometimes, we assume that getting the warnings issued is the only task that needs to be done, " Henson said. "But we're seeing that even when the warnings are out, we can still have many people killed."

He said the death toll may speak more to how people live today. "You can have perfect warnings, but if people don’t act on them … and when you have an event this big, you’re going to have some casualties. The open question is: Did there have to be 300?”

"I am concerned that there are a lot of places where safe shelter is just not a priority," Henson said.

Carbin said storms need to be studied more, particularly when many factors are involved.

"Once a storm becomes part of an environment, does it enhance wind conditions or deteriorate them?" he said. "We still don’t understand all of those interactions yet."

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Filed under: Alabama • U.S. • Weather
soundoff (85 Responses)
  1. geo

    Smartest thing ive read here is BDO's suggestion. candidradio, as someone who is constantly mobile,the weather band you speak of fades,or is not even received in alot of areas.

    April 30, 2011 at 9:05 am | Report abuse |
    • Bdo

      Its interesting that one of the main reasons people can't get out of the way of a tornado is lack of communication. Its like a bomb raid. There's only so much you can do when you hear the sirens. People have to work so they could be thinking its more important to sleep than to stay up worrying about a more than likely false alarm.

      April 30, 2011 at 10:07 pm | Report abuse |
  2. HnB

    I live in an area where I was concerned that these tornadoes may have come my way. I want to comment on whether or not we had enough warning. I do not make any effort to read the news online or watch it on tv. I do have a smart phone with a weather app from a local tv station installed. This app notifies me every time there is a warning from the NWS. Sometimes those warnings are about wind alerts, fire dangers, flood alerts, etc. I tend to ignore those warnings. But the way this app works there is a different color for the warning icon to indicate how serious the message is and I've become accustomed to that.

    So, all that was to let you know that I don't go out of my way to keep up-to-date on weather situations. On the day of the storms, I heard people at work chattering about tornadoes and how they were supposed to be very serious. We had a couple of tornado warnings/watches (I really don't remember) announced at work during the day. The skies were obviously gray. I went home and read a book for four hours – no contact with the outside media. But when I was finally done reading, I turned on the tv and COULD NOT ESCAPE the news about these storms. The local Fox affiliate broke in to American Idol (the highest rated show in the country) several times to update us. The Emergency Broadcast Service hijacked my tv programs at least twice to announce warnings. I finally got the message that these storms were really bad and turned to my favorite local news channel.

    This local news channel pre-empted regular programming with a continuous weather update (a team of 3 weathermen) WITHOUT commercial breaks until around 3 am.

    I just don't see how anyone could claim that they didn't know about these storms. I had warnings from my community, the applicable national services and my local news services throughout the entire day. The only people I can imagine that had NO way to be warned are day sleepers in MS or AL. But it seems like even truck drivers should know how to read signs of bad weather and be able to find radio stations broadcasting a warning or use the CB to talk to other drivers who may know.

    April 30, 2011 at 9:58 am | Report abuse |
  3. Soleada

    Carla & dante: how insensitive can you be? My parents actually work for the government – sub-contracted to a major trucking corporation who deals mainly in shipping military equipment. They can't get insurance, they dont get paid nearly as much as they should, & they cant afford to retire, much less seek safety when a tornado hits (they basically live in their truck). I wouldnt wish this kind of misfortune on anyone. It's sad that you feel this way.

    April 30, 2011 at 10:13 am | Report abuse |
  4. HnB

    As for having a specific tornado app... I find that you can't beat twitter for this kind of thing. I used it during a flood to find out what local areas were affected and which roads were underwater. In these kinds of cases people mark their post with a hash tag and a word that describes the situation – a topic. You have to figure out what hashtag and topic people are using for the event, but it's usually something really intuitive. Then you can search for that hashtag and topic and find out what people are saying.

    Maybe that's not the quickest way to get news out if a tornado is 2 miles away from you. But it covers much more than just one type of disaster/situation. I like the flexibility of it.

    April 30, 2011 at 10:14 am | Report abuse |
  5. Mark in SC

    Some of these conversations are really ridiculous especially the ones from some of the political right wingers (of which I m also but I am far right wing socialist in a very left wing state if it matters in this blog which I think it DOES NOT). Anyway I live in the small mountainous Northwestern portion of SC and this Spring in the South has anything but normal. The Upstate of SC is not really a tornado alley but we have had an exceptional amount of very violent storms here this year (as have my relatives also in the NE USA) that (luckily thankfully) only produced a few small tornadoes here and microbursts. I assumed that living in the mountainous area here provided me more safety than lower elevations of SC. I got home after midnight the night of the storms and had already heard that at least 15 were dead in Alabama. It was 80 degrees here after midnight and windy and wanted to see where the storms were so turned on the tube. The local stations had issued tornado warnings for all my area with a tornado on the ground across the border in Georgia and headed to MY AREA to my disbelief and I of course started to prepare to take refuge in the center of my two storied home which is about 10 years old and pretty nice and well built but with no basement which is pretty common here in this part of SC and other similar areas of the South even though we could; although many parts of the South are in the very wide Coastal Plain region and can't have basements because of high water tables. Anyway the storm missed my house by FIVE MILES and only damaged remote unpopulated areas here in SC above THREE THOUSAND FEET and had crossed into Western NC (which is even higher in elevation and close to my home) and was still making sporadic touch downs here and there, all I got here was a great light and sound show,light rain and wind as it passed nearby. Rabun county Georgia had severe damage and pretty much is the same terrain as here and many very nice Mcmansions there were among the destroyed homes there. The storm that came through here had traveled and WAS THE EXACT SAME CELL THAT DEVASTATED TUSCALOOSA AND OTHER PARTS OF THE SOUTHEAST and had traveled hundreds of miles. I hope people give these people a break when blogging and if you believe in a God give thanks that something similar didn't happen to you or yours and maybe you could say a small prayer for some of the people suffering through this I know I am and this was a learning experience for me and I thought I was pretty informed. This storm front was rare but I think will become more common as time goes on and should definitely be a wake up call for the South to create more stringent building codes and to make suitable safe havens for events like these the standard norm. Just one more thing that BLEW my mind was that NOAA kept on calling a tornado warning then changed it to a watch then canceled both then reissued them in the same order and canceled in the same order over and over for an hour (every couple or few minutes), I was shocked and am going to contact them as that was completely unsafe and ridiculous, also of interest was this storm was moving at SEVENTY FIVE MPH. If you read through my long story thanks, Peace to all of you folks and best wishes. Mark in SC

    April 30, 2011 at 10:27 am | Report abuse |
  6. Don

    Almost everyone has a cell plone these days capable of receiving text messages. Why can't NOAA send warnings to all cell carriers and then they text the warning to customers?

    April 30, 2011 at 10:38 am | Report abuse |
  7. VideeOh

    What moron publishes a video of a tornado and then puts banners over the screen covering up the tornado?

    April 30, 2011 at 12:00 pm | Report abuse |
  8. kim

    Terrible oh soo terrible the south was hit by such devastating storm just awful well that is my political correct response. Right there so much bullcrap that happen this week that went on this week the unrelentless birther, that big media bombardment of that crapy wedding, donald trumps constant attack on the president along with the tea party lunatics. Im sure the south will rise again huh.

    April 30, 2011 at 12:09 pm | Report abuse |
  9. ShanaBan

    Thats just how i feel

    April 30, 2011 at 12:16 pm | Report abuse |
  10. John

    See people, this is why we need to fund science and technology development.

    April 30, 2011 at 1:01 pm | Report abuse |
  11. Kateyofcharlotte

    You know...maybe instead of everyone on here bickering back and forth we should just send our hearts to those who lost someone or died themselves. how selfish of most of you to complain about politics in this situation. many people cant afford to move away from the affected areas and if they could how would want to? people everywhere think they got it figured out. how about instead of fighting about could have, should have's how about lets help those who are in need

    April 30, 2011 at 1:37 pm | Report abuse |
  12. Lewis

    The only way to really understand a tornado, is to be in one. I have and I hope that you never are. That is the best that I can do.

    April 30, 2011 at 2:24 pm | Report abuse |
  13. argnot

    what a surprise: another blog to act as example of the pettiness, heartlessness and honorlessness of so many people today. This disaster should, as any we face(especially on our soil), bring us closer, rather than what some jerks on the net push for. I am grateful these storms missed my mothers place(mainly), however, I know this season is just getting started. If our crazy winter was any indication of future weather, we all are in for a dose of extremes. Plan now and let's mitigate our losses next time. This was just awful.

    April 30, 2011 at 2:31 pm | Report abuse |
  14. anonymous

    On April 27, if you were in the path of that F5, it did not matter if you were in a basement. People lost their lives, being found in their basement with the entire house on top of them. As I heard it said today, "The warnings were there, people were in their safe places. It was just that bad." My friends were taking shelter in their basement and were found in the lake. This was like nothing anyone has ever seen.

    April 30, 2011 at 2:53 pm | Report abuse |
  15. Dsn63

    Hindsight certainly is 20/20. The blame game has begun too bad most of you who thought life was all about pta meetings and taking your kids to soccer games didn't plan for this.Now your cheap trac house has been reduced to a pile of broken and twisted junk,which is what it was before it was built.Funny how nature works isn't it.The ONLY ones I feel sorry for are the innocent children who were killed and injured just because their idiot parents wanted a pool in the backyard or a new Suv instead of using that money to build a tornado shelter. Don't blame the gov't for your greed! If you don't want to go through this again either build a shelter or pack up what's left of your crap and move to Maine.

    April 30, 2011 at 3:49 pm | Report abuse |
    • Dutch

      I'm glad my heart isn't as cold and calloused as yours. A sad existence you must live. All the money in the world, all the intelligent of humanity, all the political ideologies you have developed pale in comparison to just a hint of love. To make a post such as this you are without love and truly poor. I am not trying to bring you down but I do hope you wake up and join us humans and love one another as we love ourselves. It's the only way to live.

      April 30, 2011 at 8:09 pm | Report abuse |
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