National Geographic Daily News
Storms loom over El Reno, Oklahoma.

Friday's high winds snapped this power pole just south El Reno, Oklahoma.

Photograph by Chris Machian, World-Herald/AP

Ker Than

for National Geographic

Published June 1, 2013

A second wave of deadly tornadoes and thunderstorms that ripped through Oklahoma Friday night is not related to the colossal twister that tore through the same region less than two weeks ago, scientists say.

Unlike earthquakes, which are often followed by aftershocks, the storms that birth tornadoes are independent of one another.

"By pure chance, we had two separate weather systems, both in very close locations and that ended up looking quite similar," said Christopher Karstens, a research scientist with National Oceanic and Atmospheric Administration's (NOAA) National Severe Storms Laboratory (NSSL) in Norman, Oklahoma.

In addition to spawning multiple tornadoes, Friday night's severe weather triggered a flash flood and hail the size of grapefruits. At least 5 people, including a woman and her baby, are reported killed. (Related: "A Tornado Chaser Talks About His Science and Craft.")

This week's tornadoes follow closely upon another devastating twister that touched down near the city of Moore, Oklahoma on May 20, which reduced entire neighborhoods to rubble and killed 24 people.

'Tornado Alley'

What makes Oklahoma so tornado-prone? The state lies within an area of the Great Plains known as Tornado Alley, a region that stretches from South Dakota to central Texas. (Related: "Is There a Tornado/Climate Change Connection?")

Tornado Alley occupies a unique geographic position where warm humid air from the Gulf of Mexico, hot dry air from Arizona and New Mexico, and cool dry air from Canada meet, explained NSSL's Karstens.

"In the springtime, those air masses tend to work together to create environments that we saw [on May 20 and on Friday]," he added.

"Sometimes they collide in Oklahoma, sometimes in Texas, and sometimes in Kansas."

While the United States has perhaps the best historical records for tornadoes, twisters also occur elsewhere, including in Italy, India, and South America. (Related: "Lessons From Joplin's Recovery")

Another area with similar conditions to Tornado Alley is Bangladesh, said Chris Weiss, an atmospheric scientist at Texas Tech University.

"They have a lot of violent tornadoes - some would argue even stronger [storms] and tornadoes - over there," Weiss said. "But a lot go unreported because they don't have nearly the observation network over there that we have over here."

What Tornadoes Have in Common

While tornadoes can differ in their size, strength, and location, they all share certain characteristics. They are spawned from a type of rotating storm called a supercell thunderstorm.

And they are all driven by atmospheric instability and by a phenomenon known as wind shear. This happens when "wind near the ground blows in one direction, but aloft it blows in another direction. This creates shear in the airflow," Karstens explained. "If you produce an updraft within that flow, the updraft will acquire the properties of the air, and the atmosphere begins to spin and rotate."

While scientists understand some of the basic setup conditions necessary for tornado formation, there are still many fundamental questions about tornadoes that remain unanswered.

Tim Samaras, a tornado chaser known for for getting instruments inside tornadoes to measure pressure and wind speeds, says we have a lot to learn about how tornadoes form.

"We still don't know why some thunderstorms create tornadoes while others don't," he said. "We're trying to collect as many observations as possible, both from outside and from the inside [of tornadoes]."

Scientists also have a limited understanding about how tornadoes maintain their intensities and what causes them to fizzle out, Karstens said.

Tornado Forecasting

At the moment, tornadoes are much more difficult to forecast than hurricanes. For example, the National Hurricane Center was able to predict the path of last year's Hurricane Sandy with startling accuracy a full five days before it made landfall.

In contrast, even though residents of Moore had advanced warning that a potentially dangerous storm was moving in, they had only 16 minutes after the first warning on May 20 before the tornado touched down.

Part of the difficulty, Karstens said, is that tornadoes are much smaller than hurricanes.

"It's really a matter of scale," he explained. "With the hurricane being so large, we're able to populate our models with lots of points to resolve it and we can come up with much more accurate multiday forecasts."

Secondly, while current computer models can predict when a supercell storm is likely to form, not all supercell storms give rise to tornadoes.

"That's one of the questions we're struggling with as scientists: which storms will be the ones to go on producing tornadoes and which ones won't?" Karstens said.

Karstens is involved in an NSSL project that aims to predict a tornado's path shortly after it forms, called Warn-on-Forecast.

He's optimistic that tornado forecasting will improve as computers and tornado modeling software become more powerful, and as more environmental data such as temperature and dew point measurements are gathered close to tornado-spawning storms by instruments and tornado researchers.

"We've got a long way to go," he said, "but I think we're making steady progress."

Jane J. Lee contributed reporting to this article.

21 comments
summer rae roselynn
summer rae roselynn

Oh people! Look at World Events! Put them together. Started out today at hallindsey.com...every headline...war, death, flood, drought, famine, LOCUSTS?, earthquakes, storms: GOD IS BEGGING us all to repent. Suicide is an epidemic!! Hopelessness and despair EVERYWHERE! Only the Blood of Jesus and repentance can save any of us now. I have FINALLY woken and see. My suicide plans have been cancelled. GOD LOVES US SO MUCH, He is willing to warn us that time is up. John 3:16

jim adams
jim adams

I grew up in the eastern part of Tornado Alley (Southern Illinois). One afternoon in one year (about 1952 or so) from our hilltop house, i watched 11 tornadoes go across the horizon in less than an hour. I walked the ruins of several touchdowns in neighboring towns, and i got 3 years of firewood from a tornado which turned 18" trees into a tangle of pick-up-sticks. I also walked the path of that tornado from a tangle of trees around a house thru the woods for a couple miles.

Today, ANY severe storm is plastered across the headlines of papers and news programs across the country. The storms i mentioned above barely got honorable mention except by local papers. I think what is happening today is that the press is in the early stages of getting religion about Global Warming.

Elizabeth Darcy
Elizabeth Darcy

RIP Tim Samaras, Paul Samaras & Carl Young, tragically killed by the El Reno tornado yesterday. Love and thoughts to their families. Their courage and outstanding contribution to our knowledge of tornadoes will live on forever x

Michael Bedar
Michael Bedar

For more possible reasons for repetitive localized storms worthy of scrutiny, look up HAARP and the current HAARP status, a technology usable for convenient distractions as well as destructive attacts, and I don't even have to conclusively believe HAARP is the cause to at LEAST expect it to be in the discussion as to why Oklahoma is being "tornado-vexed" right now. An honest investigation would explore the existent theoretical physics of an electric ionosphere frequency technology, and the HAARP program should at least be considered as evidence demanding further exploration as to its probability level of having a relationship to the seen phenomena at this time in Oklahoma.

Carey Hoffman
Carey Hoffman

Tornado science is fascinating, and it looks like we are on the threshold of having the technology to learn some important answers.

But science is science, and one popular perception that you pick up in the press and social media is that this is a terrible year for tornadoes. Statistically, that's very far from the truth. We've only had about one-third the number of tornadoes we usually have on average at this time of year so far, and even with May picking up the pace, the month we just finished was just over 80 percent of the normal amount of reports we expect in an average year.

Yes, things have been dramatic in the last two weeks and, yes, the May 20th Moore tornado was exceptionally strong, but until the weather pattern of the last two weeks set in, it had been a very quiet year statistically. Beyond the severity of the Moore tornado, the other factor that skews public perception is the preponderance of video documentation of each storm on YouTube and other sources. Each bad storm becomes more personally experienced by each of us, and thus grows in fascination and reacting to it really becomes a social experience. The media further pick up on this, and then you end up with an article like this on National Geographic, when actually the more scientifically relevant question to be asked at this point is what factors have made 2013 so quiet thus far?

Carey Hoffman
Carey Hoffman

Tornado science is fascinating, and it looks like we are on the threshold of having the technology to learn some important answers.

But science is science, and one popular perception that you pick up in the press and social media is that this is a terrible year for tornadoes. Statistically, that's very far from the truth. We've only had about one-third the number of tornadoes we usually have on average at this time of year so far, and even with May picking up the pace, the month we just finished was just over 80 percent of the normal amount of reports we expect in an average year.

Yes, things have been dramatic in the last two weeks and, yes, the May 20th Moore tornado was exceptionally strong, but until the weather pattern of the last two weeks set in, it had been a very quiet year statistically. Beyond the severity of the Moore tornado, the other factor that skews public perception is the preponderance of video documentation of each storm on YouTube and other sources. Each bad storm becomes more personally experienced by each of us, and thus grows in fascination and reacting to it really becomes a social experience. The media further pick up on this, and then you end up with an article like this on National Geographic, when actually the more scientifically relevant question to be asked at this point is what factors have made 2013 so quiet thus far?

Jim Renton
Jim Renton

Why can't the media get this straight. OKLAHOMA IS NOT THE MIDWEST. OKLAHOMA IS THE SOUTH CENTRAL

Christopher Kavanaugh
Christopher Kavanaugh

Oklahomans have known for many years that the answer to this question is because Texas Sucks.

Jorge Lopez
Jorge Lopez

Obama's fault and left wing liberals are doing it!!

margaret jones
margaret jones

@jim adams @jim adams  Thank you Jim for the long term perspective which is also often totally ignored. If a tornado wrecks a few trees or some poor farmers lively hood and home the media doesn't even notice. But as we build cities in tornado prone areas each one becomes a national disaster and media frenzy because the number of people affected rises...not because the tornado was stronger or less deadly to any in it's path.

Alec Sevins
Alec Sevins

@Michael Bedar These HAARP conspiracy theories are tiresome. Tornadoes are driven by warm air contrasting with cool air, not antenna signals from Alaska. The real acronym to worry about is AGW (anthropogenic global warming).

Amended standard disclaimer: "While no individual storm can be blamed on global warming, it would be mindless to pretend that increased heating of the global atmosphere has no relation to heat-driven storms."

Alec Sevins
Alec Sevins

@Carey Hoffman I hope your post isn't a subtle form of a global warming denial. The increasing preponderance of major heat-driven events, including droughts, fires and hurricanes well north of the equator can't be ignored in the context of a warmer atmosphere. 

Tornadoes specifically may be hard to put in that context, but they are logically driven by more heat colliding with cool systems. Increased population density in tornado zones is yet another factor, but let's stay focused on the bigger picture.

Victor G.
Victor G.

@Jim Renton 

Jim, please.  It's the midwest.  It may be south central, but it's the midwest, the great plains, ya dig?  There's the upper midwest, south central, etc. etc, but it's between the mideast and the west, so it's the midwest!  They did get OK straight.  Anybody can look on a map and see where it is. 

Carey Hoffman
Carey Hoffman

@Alec Sevins @Carey Hoffman No global warming denying here, Alec. There could be a connection, but whatever it is has yet to be established. Global warming is likely a meta-level factor that sets the stage for regional tornadic events, like we saw Friday (if, indeed, it turns out to be a factor of causation.) No doubt, though, that it is having any number of other influences on weather.

I'm interested in the context of this story of what causes one storm to produce a strong tornado and another very similar storm 20 miles away to produce nothing but straight-line winds. As to the big picture, that's exactly what my post was trying to point out -- the big picture fact on prevalence of tornadoes this year is exactly the opposite of what the narrative is being made out to be currently in the popular media and public discussion.

Jim Renton
Jim Renton

@Victor G. @Jim Renton 

 Maybe you should research what constitutes the midwest. The census doesn't put Oklahoma in the Midwest and neither does the AP Stylebook, which journalists should follow. Oklahoma is southern by nature, both culturally and geographically, and has nothing in common with Iowa or Illinois.  Midwest does not mean middle.

margaret jones
margaret jones

@Carey Hoffman Thank you for such a balanced point of view. There are such a multitude of temperature, moisture, wind sheer, perhaps even chemical elements of air factors that could potentially affect tornado and storm activity that to focus on any one element before researching others is not going to get us to the answer. Interesting points you have made.

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