Single-Shot Tornado Analysis

22 May


My condolences to those who have suffered in Moore, Oklahoma when a 200+ m.p.h. tornado half a mile wide ripped through a suburb of Oklahoma City, Oklahoma. Currently, 24 people are confirmed dead and 237 are injured. Photographs of the aftermath of the tragedy resemble a war zone. Analysis of the shocking meteorological disaster have focused on climate change.

AMY GOODMAN: Jeff Masters, why is this area of Oklahoma—why is it so vulnerable?

JEFF MASTERS: Yeah, poor Moore, Oklahoma. I mean, they’ve been hit by three EF4 or stronger tornadoes in the past 14 years, including the most intense tornado ever measured: 302 mile-per-hour winds in the 1999 storm. And I guess it’s just bad luck, because you would expect other areas, you know, should have gotten that kind of pummeling, you know, not so much concentrated in area like Moore. I mean, downtown Oklahoma City has never been hit as bad as Moore has been hit. And I don’t know how to describe, you know, what accounts for that bad luck. Maybe there is some sort of terrain effect we don’t understand that makes that area more vulnerable than, say, downtown Oklahoma City.

AMY GOODMAN: How does this tornado compare to the one right there, right nearby, in 1999?

JEFF MASTERS: Yeah, yesterday’s tornado was larger and covered a bigger area, maybe at least twice as large. As far as the top wind speeds go, we’re not really sure how strong the winds were in yesterday’s tornado. We’ve been given a preliminary rating of EF4, which means 166 to 200 mile-per-hour winds, by the National Weather Service, but they haven’t done detailed damage surveys yet, and it’s quite possible they’ll upgrade this to an EF5, which means winds in excess of 200 miles per hour, certainly very close to a top-end sort of tornado. They don’t get much stronger than this.

AMY GOODMAN: You think this could be the largest in history?

JEFF MASTERS: It will certainly rank up there in the top 10 or so, I think. And, you know, we don’t have a very long history. We go back to about the early 1950s as far as, you know, measuring how big these storms are. And we didn’t have radar until, oh, the 1990s, as far as being able to look on a Doppler radar how big these storms are. So, it’s certainly going to be one of the biggest in history. We don’t know, you know, if it’s going to actually be a record-breaker at this point yet.

AMY GOODMAN: Jeff, what is the connection? Is there a connection between this tornado and global warming?

JEFF MASTERS: That’s a tough call. I mean, it’s an important question. And we really have a huge area of unknowns here to try and answer that question. The big problem is the tornado database isn’t very good. It only goes back about 60 years. And we don’t measure tornadoes directly. They have to run over a building before we know how strong they are. So we’ve got a lousy database. And our computer models to study tornadoes aren’t very good yet. We don’t understand what makes them tick very well. So, even with our highest-quality, finest research models, can’t tell you what a tornado is going to do and how it’s going to form, we can’t expect our climate models to do that sort of math, either, because they’re a lot courser. They can’t look at the fine details very well. So, a lot of uncertainty about how climate change might affect tornadoes.

I might add that over the past 12 months, we’ve seen the record lowest number of tornadoes in U.S. history, at least the EF1 and stronger tornadoes. But back in 2011, we saw the record highest 12-month total of tornadoes. So, we’ve just been getting kind of weather whiplash with our tornado seasons. I mean, going from the extreme highest to the extreme lowest, that’s really tough to, you know, say what is the trend going to be. Well, it might be one or the other. And at this point, I can’t identify what climate change is likely to do, which of those type of years we’re more likely to get.

AMY GOODMAN: In 2011, after a series of large tornadoes, Kevin Trenberth, head of Climate Analysis Section of the National Center for Atmospheric Research, said, quote, “It is irresponsible not to mention climate change. … The environment in which all of these storms and the tornadoes are occurring has changed from human influences.” Your response to that, Jeff Masters?

JEFF MASTERS: That’s right. Every weather event is substantially changed now by climate change. There is more heat in the atmosphere. There is more moisture. And something I’ve been seeing the last three years is the jet stream patterns have been getting very extreme. I’ve never seen, in my 30 years as a meteorologist, the sort of unusual sorts of jet stream patterns where we get these large loops, where they tend to get stuck in place, contributing to extreme weather. Whether we’re going to be seeing more tornadoes because of that, I don’t really know, because when you do change a jet stream like that, you are actually going to slow the winds down of the jet stream. And when you have slower winds, you get less of a twisting motion to get tornadoes spinning. So, in theory, that should decrease tornadoes. But on the other hand, when you have a warmer atmosphere, the air is more unstable, and that’s the other key ingredient we need to make tornadoes. How those two factors are going to interplay in the future, we don’t know. But I think Dr. Trenberth is right: We have to look at the changed environment that all these sorts of weather systems are in now to look forward to what we’re going to see in coming decades.

Yet, it’s always prudent to avoid the fallacy of the single cause, and look at the interplay of multiple factors. Nate Cohn offers a multiple factor explanation for the EF-5 tornado at Moore.

It’s tempting to assume that climate change is responsible for an increase in the number devastating tornadoes, like those that ravaged Joplin, Missouri, in 2011, and Hattiesburg, Mississippi, in February. But if these tragedies are indeed becoming more common, it’s mainly because of population growth. Sixty years ago, yesterday’s tornado might not have killed anyone at all: Moore had a population of 942 in 1950, but today has more than 56,000 residents.

There has been an increase in the number of reported tornadoes: Since 1950 (or even over just the last two decades), the U.S. has added Doppler radars capable of detecting tornadoes, and population growth has increased the number of on-the-ground observations. But it’s unclear whether tornadoes have become more frequent, let alone because of climate change.

A NOAA study cast doubt on the climate change case, since the conditions that tend to produce tornadoes—like an unstable atmosphere and wind shear—haven’t become more common over the last few decades. However, the number of days with extremely high levels of atmospheric instability (Convective Available Potential Energy, or CAPE) has risen since the 1970s, and climate models suggest that higher levels of atmospheric CO2 could further increase the number of days with high CAPE levels.

If true, more powerful tornadoes might become more common, bringing more tragedies. Further improvements in tornado warning lead-times might save a few more lives, but unless you have a tornado shelter, there’s no place to hide from an EF-5 tornado. Unfortunately, the residents of Moore learned that first-hand on Monday.

But, don’t tell Oklahoma’s senators they might have to authorize Federal spending to correct for these lessons – they know the gospel of austerity trumps even acts of God, like a freakishly powerful tornado.


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