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. estebangonzolaz

    Thank you CNN for reporting about the efforts of Richard ST. Dennis for sending the poor people in Mexico Wheelchairs for the disabled who can not afford to buy one. A true hero!!! Lets hope he can continue and we can develop stronger ties between Mexico and The USA and help the poor. Richard needs help to continue to do his good work and those with the capability should help. No one ever let use know how we can help him in any way?

    April 29, 2011 at 2:27 pm | Report abuse |
  2. Sarah

    As a citizen living in Alabama, it is horrible to see this happen again after having lived through the tornado that struck Enterprise. My prayers go out to everyone effected by these storms.

    April 29, 2011 at 10:44 pm | Report abuse |
    • Andrew Tyler


      April 30, 2011 at 9:46 am | Report abuse |
    • Gsan

      Oh boy Andy. It is people as yourself that make us think negative of the 'Dorks' that roam this earth.

      April 30, 2011 at 1:46 pm | Report abuse |
    • Steven

      To anonymous:

      Actually, it's "bite", not "byte". And to the OP, excellent post.

      April 30, 2011 at 2:14 pm | Report abuse |
  3. Sarah

    Hey CNN, all day Wed you had Donald Trump and drama. Barely anything about the storms as they marched across AL. Unless these folks are watching weather channel no one knew the gravity.

    April 29, 2011 at 11:06 pm | Report abuse |
  4. Laura

    It's not that safe shelter isn't a priority, it's having the money to build a basement. The premade storm shelter bubbles cost at least $3000. My family lives in east limestone between Madison and Athens, Alabama. The older houses have basements or storm shelters but the new ones don't. Builders are buying up flat farmland and putting large neighborhoods on it, with slab foundations. The damage spans a mile wide taking even brick homes down to the slab – we are used to tornadoes taking out trailers and roofs off of brick homes, but not this. Most of my neighbors are transplants, where do u go other than the closet or the bathroom floor when u don't know anyone with a basement and there are no community shelters?

    April 29, 2011 at 11:13 pm | Report abuse |
    • glu

      Its simple, dont buy a home without a basement. Slabbed homes are garbage anyway as you cant work on them when you need new electrical/plumbing.

      April 30, 2011 at 9:47 am | Report abuse |
    • memmom

      To GLU–It is not that simple. Most homes in this part of the country do not have basements. The water table is too high.

      Laura–I agree with you. We looked into getting a shelter and it was going to cost more than $10,000. It seems that the government ought to be able to offer a tax write-off for people who install a shelter–something similar to the energy-efficiency write-off.

      Also, part of the tornado problem is the lack of secure shelters; part of the problem is that the populace is desensitized to the warning sirens. Where we live, they go off whenever a tornado is spotted within the county–which covers miles and miles. That means the sirens go off frequently, and the "hit and miss" nature of tornadoes means you can spend hours sitting in a closet when there really isn't imminent danger in your particular area. After seeing the destruction of this storm, more people will probably heed the warnings (at least for awhile). The warning systems are antiquated–I would love to know the last time they were updated. We've lived here for 20 years and the system seems to be the same.

      April 30, 2011 at 10:34 am | Report abuse |
  5. Mike

    I know it seems like a huge endeavor, but just as you have stringent building codes in earthquake and hurricane zones, I think that although it wont save everyone but some kind of reinforced room or basements should be required in every new home in tornado prone areas. Mobile home parks should have an underground shelter for its residents as well. Yes it will cost money, but that money can be offset by discounts in your insurance premiums. These safety measures can also be paid for by the FEDERAL GOVERNMENT. We don't have a problem firing off over 100 million dollars worth of cruise misiles to scare the leader of Lybia while the price of gas continue to rise. 1 million dollars or 1 cruise missile could have built at least 1000 safe rooms. I think believe that each American life lost in Wednesdays storms are worth more than any dollar figure. We can rebuild but we can't bring back our friends and loved ones. JUST SAYIN.......

    April 29, 2011 at 11:32 pm | Report abuse |
    • fishnn machine

      I agree.....its funny how we are suposely in debt up to our necks but we can spend billions on bailing out company's and blow up ever coner of earth but we can't protect our own.....gees god please bless america...

      April 30, 2011 at 9:02 am | Report abuse |
    • paul

      This is the time of year when various authorities release lists of words, phrases and acronyms that have recently joined the English language: "BFF," "retweet," "unfriend" and "vuvuzela" made many current lists. I'm glad for all of them.

      But there is one phrase that I hear most every day that I don't like at all: "I'm just saying."

      Its origins are murky. Some people swear they heard it in an early Eddie Murphy routine. Others insist that it dates from Seinfeld episodes. In any case, the roots of the phrase seem to be sitcom, not Shakespeare — I'm just saying.
      A man shrugging.

      Each week, I get emails and messages that go something like, "You are witless, stupid and immoral, and I wouldn't let you near my tropical fish for fear you would contaminate them with your depravity. Just sayin'!"

      Saying, "I'm just saying," puts a fire escape onto the end of a sentence. It lets you express a stern — even rude — opinion, but not really. You're just saying. It invites the listener to discount what we've just heard, even as we're reeling from it.

      The Urban Dictionary website explains that the phrase makes it "possible to deliver a rude comment or burn and have it bounce off simply as an opinion disguised as an objective opinion, and who can argue with you over an opinion that you don't apparently support."

      April 30, 2011 at 9:25 am | Report abuse |
    • fishnn machine

      Hm? So what exactly are you saying?you now what I'm saying!

      April 30, 2011 at 10:09 am | Report abuse |
    • willr

      So whatcha sayin is that sayin 'Just sayin' is used to say something just to say? Is that whatcha sayin? Just sayin.

      April 30, 2011 at 1:05 pm | Report abuse |
    • horsedorkque

      Fuk U...I keel America!!!

      April 30, 2011 at 1:44 pm | Report abuse |
  6. 1609

    Jazz is a loser

    April 29, 2011 at 11:43 pm | Report abuse |
  7. mdmooser

    It was in the 1974 super outbreak in central Kentucky, Richmond Kentucky to be exact. To make a drama filled response shorter, The only time in my life I have seen a tornado or tornadoes was that first night when I saw 10 – 12 tornadoes at once. Yeah, that's right all around me as everyone else was looking at the damage around them just outside of town, I noticed the tornadoes all around us and yelled out, hey look around us and the state police officer, yelled out,"I want all of you to get in your cars and drive as fast as you can, get home and fill up your bathtubs you will need the water."

    April 30, 2011 at 12:23 am | Report abuse |
  8. Adam

    I feel for all the folks affected by this historic outbreak.

    That said, even sheltering in a "safe place" above ground will not protect you from violent EF3 to EF5 tornadoes. Even basements are unsafe for such super outbreaks. The only safe place to be in storms like these is underground in a dedicated tornado shelter. It is not feasible for every home to have such shelter. Proper warnings and possibly large underground public shelters are the only recourse.

    April 30, 2011 at 12:32 am | Report abuse |
  9. Soleada

    my parents are truck drivers.. I was beyond worried about them. Thankfully they're okaay, but 2 of their friends – another couple who drive truck as well – got hit by 1 of the tornadoes, while they were sleeping in their truck no less.. The tornado turned the truck over & both of their friends went to the Hospital. the lady had a broken nose & some other injuries. not sure what happened to her hubby. I agree with Adam when it comes to mass underground shelters.. My parents, along with many other truck drivers &/or transient travelers or whatever need to have that kind of access to safety in hazardous conditions.

    April 30, 2011 at 12:44 am | Report abuse |
  10. Andrea M

    First off, if the sky is turning green, get inside. This is a standard weather safety rule. Don't wait for the NWS, if it's green, seek shelter. First choice is a sturdy building with basement. Second is anything that has a closet. If you live in a trailer, make sure you have a will filed then get under your bed. Ideally, don't live in a trailer in the midwest or south, God hates trailers.

    April 30, 2011 at 12:49 am | Report abuse |
    • Tornado Alleycat

      Green and purple is double bad.

      April 30, 2011 at 9:04 am | Report abuse |
    • Name*PHILIP what color is the sky at NIGHT?

      April 30, 2011 at 11:04 am | Report abuse |
  11. PJB863

    In many countries around the world, underground or hardened above ground shelters are part of building codes, not only for weather related phenomena, but as a civil defense measure (Israel comes to mind). We, in the U.S. sort of did this in the 1950's with in-home bomb shelters. My grandparents' house had one, which was used mostly for storing preserves, etc. that my grandma put up each year, but also stored important papers, etc. in. It was also where we went whenever a tornado was threatening the area. It wasn't especially costly – it was a small room off the basement, built when the house was built. Doesn't seem like such a bad idea now, does it?

    April 30, 2011 at 12:56 am | Report abuse |
  12. DanteX

    Mike you are an IDIOT.

    First – The FEDERAL GOVERNMENT did the job it was supposed to do by warning people of the IMMENENT DANGER that these storms would cause through the the agencies called National Weather Service and the Storm Prediction Center. The same TEA Party IDIOTS that cry and scream and yell about "an intrusive Federal Government" are now the very ones out there begging and crying and pleading for the Federal Government to "come help us" or "where is my check?"

    Second – The responsibility fo BUILDING CODES rests with the States – NOT with the Federal Government. Every person that lives in "Tornado Alley" KNOWS that tornadoes ARE A FACT OF LIFE – INCLUDING the Legislatures of the States that make and pass laws where tornadoes happen. More importantly – This is mater of PERSONAL RESPONSIBILITY. THAT IS RIGHT. IF you KNOW you live in an area that is proto tornadoes and you decided to settle on buying a cheaply built house or one that has no basement or storm shelter – THEN THAT is YOUR fault and YOUR responsibility. The Federal Government -and my tax dollars- are NOT responsible for your stupidity. So when your Insurance Company -if you had the brains to have insurance- gives your check to "rebuild" – Maybe you will build a house with a basement or a storm shelter. Or Better Yet – Maybe you will BUILD A BETTER HOUSE.

    You Want Help? Go see your Republican Governor and his "States' Rights" Republican-dominated Legislature and ask THEM for the "help" you need since according to them "the States' can do a much better job at running things than some Federal Bureaucrat can."

    Better Yet – Go to your local TEA Party Chapter for "help." I am sure they will be willing to "help" you – If they are not too busy lobbying your Republican Governor and the Republican Legislaature.

    April 30, 2011 at 12:58 am | Report abuse |
    • Jacob Jones

      First: The fact that you still spew politics when discussing tragic loss of human life should be a wake up call pal. This is a human issue. This has nothing to do with tea party, democrat, republican.

      Second: You cannot build a house/apartment strong enough to withstand 200+ MPH winds from an EF4-EF5 tornado without spending many thousands of dollars. Too bad money doesn't grow on trees down here.

      Third: From a democrat living in Tuscaloosa, Alabama: Go f*** yourself.

      April 30, 2011 at 1:37 am | Report abuse |
    • carla

      Thank you DanteX. I have posted similar things with little success. As much as I feel horrible for families who lost loves ones and their homes, I am getting really tired of people wanting government out of their lives until it's convenient for them. Although Jacob would like to believe this is just a human issue, he is so wrong. I lived in tornado alley for 8 years. Plenty of storms. I live in Minnesota now where we also get them. You are so right, when the sky turns green, get inside. Don't worry about taking that awesome video to post on youtube or face book. Don't go out and stare at the dang thing. Get your dang butts inside. Everyone knows this, especially living in these areas. The nat'l weather service can call you personally on the phone and tell you it's in your backyard but they can't make you smart. Next time one of these red states want less government, they may want to think about last wednesday again and see if maybe, at times, people need help and we can't always do it ourselves. They may want to stop griping about paying those taxes so that we can keep emergency folks available to dig you out when a tree has fallen on you from that forecasted tornado. That big old bad government isn't looking so bad right now is it folks. Remember that at the next election.

      April 30, 2011 at 1:57 am | Report abuse |
    • carla

      @jacob. Instead of telling Dante to go F himself. You should look around at the devestation around you and be thankful you are not one of the near 300 who have perished. I'm betting there are a lot of ppl help you already. Be thankful sir. You would think a close call with meeting your maker would make you a little more humble. Contact your governor and tell him he should have taken some of that stimulus money to help build the sturdy shelters..

      April 30, 2011 at 2:00 am | Report abuse |
    • Jacob Jones


      I've had a long couple days. I am thankful to be alive and spoke a bit strongly with the GFY comment. To see what has happened to my town being turned into a political discussion sickens me quiet frankly. It is not a discussion I will partake in. All the best, and please keep my town in your thoughts and prayers. Regards,


      April 30, 2011 at 2:40 am | Report abuse |
    • Amber

      One big problem there, alot of the areas that were hit with the tornadoes weren't in "tornado alley" my hometown (barnesville, ga) was devastated in this storm & guess what? no one there can even recall when the last tornado that touched down there (that didn't dissipate in like 5 seconds) was! It isn't a matter of 'personal responsibility', it was a freak storm! Why would people in a town as poor as barnesville pay to have shelters built when something like this has never happened before!?!? Not to mention, if they live in a trailer, do you really think they can afford to build some sort of storm shelter?

      April 30, 2011 at 2:46 am | Report abuse |
    • wow really

      Well dantex,

      In a perfect world where there is plenty of money to go around and jobs for everyone building a perfect home with a perfect shelter would make sense wouldn't it?? The fact is that many people that were affected by these tragic storms are infact poor or middle class people who can barely get the loans to finance their "crappy and cheap" homes. Unfortunately, the major banks in this country FAILED and were handed a HUGE stimulus to avoid being shut down. Now these same banks will not lend to people with perfect credit scores. You (I assume sir) are the idiot because we do not live in this fantastic utopia you have described by your post. We live in a nation that is on the brink of bankruptcy, yet sends billions of dollars to other countries when they are in a time of need. You need to wake up and realize that yes the government should be held accountable to an extent, and more then anything, you need to realize that these kind of events are rare and even in the "safest" place to hide mother nature has ways to spew destruction, and that as fellow citizens we owe it to our countrymen and women to lend a helping hand when we can.

      April 30, 2011 at 3:08 am | Report abuse |
    • Tornado Alleycat

      You and Carla are the real idiots. Do you even pay taxes? Probably not.

      April 30, 2011 at 9:07 am | Report abuse |
    • fishnn machine

      Lmfao JACOB JONES man that was funny stuff ,you hit the nail in the the third one.......some people are so stupid..qqz

      April 30, 2011 at 9:14 am | Report abuse |
    • fishnn machine

      Carla go ff your self ........hope a tornado goes up your a hole

      April 30, 2011 at 10:05 am | Report abuse |
  13. spider

    Ever hear of the haarp project? Look it up.

    April 30, 2011 at 1:23 am | Report abuse |
  14. Mike

    Sorry Dantex... I am not a republican or a tea party member. My house is well built and I simply said for the sake of those who have to REBUILD that it should be required so if necessary to have a safe place to go. This Country experiences almost every natural disater known .. be it earthquakes, hurricanes, floods, and let's not forget man made as well. I don't know where the hell you live where you are not vulnerable to at least one of these. Please tell us so we can move there. And like I said if we meaning the Feds can spend billions of dollars a year fighting in unjust wars trying to make countries believe as we believe, trying to bully Eastern countries that has lost all respect for us. BTW. I served in operation desert shield / storm. Then its not a matter of what your party is or what state you live in. I also said it wouldn't have saved all but even one less would be worth it. I AM FOR PEOPLE , NOT CORPORATIONS. . . Put your political issues to the side. At what value do you place human life. F@#$ a check these people DON'T HAVE ANYTHING LEFT.. Insurance companies can't get your family heirlooms back, or your forty or fifty year old baby pictures. $3000.00 – $6000.00 to save a families life after they have lost everything else, is a small price to pay. I have friends here that lost friends Wed. as those tornadoes tore thru my County less than 5 miles from my home. TELL THOSE PEOPLE THAT THEIR LIVES WASN'T WORTH IT. U MO%@*&F!#@$%& IDIOT.

    April 30, 2011 at 2:48 am | Report abuse |
    • fishnn machine

      Yes go ffffkkkk your self dexter! Hope a tornado goes up ur a hole : (

      April 30, 2011 at 10:19 am | Report abuse |
  15. Mike

    Also Dantex, I am an Arican American man living in the United States and has had to work for everyhingi have. A.A. make up less than 15% of this country and they all don't feel the way I do. Know matter where I go I will be outnumbered, but and will stand by anything I say. And I will continue to help those less fortunate than I ....... NOT JUST WHEN DISATER STRIKES

    April 30, 2011 at 3:02 am | Report abuse |
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