December 30, 2011

Was the Joplin Tornado the Deadliest We Can Expect?

Filed under: Severe — Erin @ 10:58 pm

Meteorologists and weather-watchers are bidding the year 2011 a less-than-fond farewell.  While it was certainly a banner year from the point of view of storm chasing—6 EF-5 tornadoes, 17 EF-4s, and many of them highly photogenic, as the dozens of home videos on Youtube illustrate—it was a catastrophe in terms of the human impact.  With 552 fatalities, this year is tied for the second-deadliest tornado year in the U.S.  The death toll is an order of magnitude greater than even most of the “bad years” of the 1975-2010 period.  Two events are primarily responsible for this:  the April 27 Dixie Super Outbreak, which killed over 300 people (breaking the 1974 Ohio Valley Super Outbreak’s grim record by a hair), and the Joplin, MO EF-5 tornado, with approximately 160 fatalities.

With the 2011 Super Outbreak, meteorologists are starting to work out an approximate historical return period for these large-magnitude events.  Before the 1974 event, the last comparable event occurred in 1936, with an outbreak popularly known as the Tupelo-Gainesville outbreak for the violent tornadoes that occurred in Mississippi and Georgia.  It seems that these huge events occur approximately every 35-40 years.  Obviously, a comparable event could occur next spring, but statistically, it seems that they are a 35- to 40-year event.  And, given that the 1974 Super Outbreak and 2011 Super Outbreak saw comparable death tolls, I think we can also estimate what the human toll for such an event will unfortunately be as long as the affected communities have unsuitable safety options for EF-4 and EF-5 tornadoes.

The Joplin tornado is a different beast.  We do not have a comparable modern event.  Individual tornadoes in 1953 killed over 100 people in Waco, TX and Flint, MI, but that year was something of a catalyst of public outrage, for a third tornado in Worcester, MA killed 94 people.  Public sentiment that year was essentially, “DO something so that this never happens again!”  And for 57 years, no single tornado in the U.S. did kill over 100 people.  Then… it happened again.

Was the Joplin event a worst-case scenario?  Is this the deadliest (give or take) that a single tornado can actually be now?

I think the answer to the first question is a guarded “yes,” at least for the specific case of a tornado striking a city.  The tornado was about as strong as they come; its winds were estimated to be up to 250 mph.  They can get more intense than that, but it doesn’t make a lot of difference in terms of structural damage.  The tornado rapidly intensified precisely as it entered the heavily populated regions of Joplin, and it passed right through residential and commercial shopping areas—the worst areas it could strike.  Examination of the track shows that there was also a pretty large corridor of EF-4 and EF-5 tornado damage, which would be expected for a wedge tornado.  Sometimes the area of violent damage is comparatively small, but this was not the case with this tornado.  Storm cellars were rare in this area, making survival above ground mostly a matter of good luck.  The tornado was also rain-wrapped for much of its existence.  In terms of the storm’s power and the location of impact, you can’t get much worse than this.  However, I should note that it occurred on a Sunday.  Some have argued that if it had happened at the same time of day on a work day, it could have been worse.  We don’t know for sure, and let’s hope we don’t find out.  I tend to think it probably would not have been much worse, given that residential areas (not a likely area for commuters to be stranded) and the shopping district (which probably would get more foot traffic on weekends than work-week afternoons) were such a large part of the damage zone.  In my opinion, the Joplin tornado was essentially a worst-case scenario for a tornado striking an urban area.  A comparable tornado striking an urban area probably would have a comparable human toll.

Unfortunately, the second question—is the death toll of ~160 the highest we could see for a single tornado in the modern era—has a different answer.  There are two ways that a single tornado could kill a lot more people than that.

One is the possibility of a weak, poorly-built or dilapidated high rise building taking a direct hit from a violent tornado and collapsing with a lot of people inside it.  Generally, these buildings are not supposed to collapse even in EF-5 events.  Images of collapsed high rises on hurricane landfall sites are misleading; these buildings mostly had shallow foundations and were undermined by the storm surge.  They were not blown over by wind alone, and storm surge is obviously not a factor for tornadoes.  The St. John’s Hospital building in Joplin took a direct hit from the tornado when it was at EF-4 intensity and it did not collapse.  However, a poorly-constructed or dilapidated one could.  (As an aside, one does have to wonder about the possibility of a tornado tearing up ground several feet deep, as happened in the EF-5 tornado on April 27 in central Mississippi. This could definitely undermine a slab foundation on a house, resulting in the foundation being ripped from the ground—the supposed hypothetical “F6 intensity” signature that one heard bandied about prior to the adoption of the Enhanced Fujita Scale.  However, high-rise buildings have much deeper foundations than residential homes.)

The other possibility is that of a violent tornado striking a crowded spectator event, such as a sports game, a fairground, a speedway, etc.  This possibility has been discussed at length by meteorologists such as Dr. Roger Edwards of the Storm Prediction Center.  It’s almost happened before, in fact; in 2008 an EF-2 tornado in Atlanta, GA struck the Georgia Dome while a basketball game (involving my college team) was going on.  It had gone into overtime, so people were not milling around outside.  Still, there are videos from that event of pieces of the roof collapsing and falling to the floor while the spectators were left to fend for themselves in the stands.  A stronger tornado could very easily have taken that roof off.

So yes, although the Joplin tornado was very likely a worst-case event for a tornado strike on a city, thereby representing an approximate limit on fatalities for that type of disaster, the potential exists for individual tornadoes to kill far more people than that in a different sort of disaster.  Let us hope that we can deal with the infrastructure and the safety considerations of large venues so that these greater disasters do not occur, either in 2012 or years to come.

October 19, 2011

NWA 2011: Thoughts About Tornado Warnings and the Casualty Count

Filed under: Severe — Erin @ 7:56 pm

I attended the National Weather Association’s conference in Birmingham, Alabama, for two days.  Toward the end of the second day, the main focus of the talks was the terrible death count from tornadoes for 2011, and most of the speakers were coming at the problem from the perspective of social science such as psychology.  It is understandable that people would want to better understand what happened in an anomalous, outlier year such as 2011.  It is understandable that people would want to find out if the catastrophe was a result of factors that can be easily changed, and that they would even be biased toward that hypothesis.  (One presentation even mentioned the “optimism bias”—a concept that seems a bit strange to me as a natural pessimist, but I can readily see that it would exist in most people, and I would say that this is a perfect example of it.)  My intention here is not to call anyone out.  However, I think that a lot of the research is, frankly, barking up the wrong tree.  There are also some very serious flaws with some of the studies themselves.

The bulk of the research involved surveys of people from the areas that were impacted by tornadoes in 2011.  The surveys contained questions about NOAA watches and warnings (whether people received them, how they received them, whether they were understood) and people’s responses to these messages.

Here are some points I took away from the social science presentations:

  • An overwhelming majority of people in impacted areas did receive warnings.
  • A very small minority of them immediately went to shelter after receiving a warning from the first source.
  • A rather large plurality sought out additional information from TV, the Internet, or personal confirmation to determine if the tornado actually existed and would potentially affect them.  This was more likely in people with higher levels of education and in people who knew more about the weather.  (I would like to note here that this is exactly what I did when the east-central MS EF-5 tornado of April 27 was heading my way.  I did not immediately barricade myself under the stairs when I heard the warning.  I looked at radar to identify a probable debris ball signature and plotted its projected path to go right over my house.  I then grabbed my cat and got out of town.  The tornado lifted, but if it had stayed on the ground, I could have been killed as a result of following the canned advice rather than reasoning out the best course of action for myself!)
  • A minority of people chose to completely ignore a warning.
  • When asked how likely they, personally, thought it was that their area (of what radius?  I don’t recall if it was stated) would be significantly impacted as a result of bad weather mentioned in a warning, the most common answer was less than a 25% chance.  The social scientists said that they wanted people to guess a nearly 100% chance, but in fact, the scientifically and statistically correct answer was less than 5%.  Interestingly, this arguably refutes the “optimism bias” argument in that people did give a more pessimistic judgment of their risk level than was really the case, just not pessimistic enough to suit the social scientists.

The social scientists seemed to be dismayed by the fact that people were less likely to immediately dive for cover the more educated and weather-savvy that they were.  Needless to say, this is an odd message to deliver to a room full of meteorologists (many of whom actively seek out bad weather in their vehicles).  What is the point here?  “Ignorance is strength,” to quote from Orwell? Let alone that people can’t exactly become less weather-savvy, less educated, or more paranoid about the personal impact from a storm if they already know better.  This is an example of trying to close the barn door after the animals have escaped.  These things are what people do, and with the proliferation of web phones with more and more features that allow people to have access to information virtually anywhere, these behaviors are only going to become more common.  This means that they are the behaviors that must be worked with and planned for.  Trying to force people into a state of unnecessary and statistically unwarranted fear is not going to work.  Nor is it a good idea to try to bully people into not seeking out information and using cognitive reasoning.  I’m no social scientist, but I can tell you that if this is attempted, the most likely reaction is a rebellious contempt for “the government” for “trying to make us not question, not think for ourselves, and do as we’re told.”  I would be just about willing to guarantee it.  It could backfire badly.  People ultimately have to be responsible for their own decisions.

Furthermore, there was absolutely no evidence given that people who sought out more information first were more likely to be injured or die in an event, and obviously the survey methodology required interviewing people who did not die.  Knowledge about what the people who died did must come from people who were with them and survived.  However, I never even saw that there was a distinction made between the group of people who were in the path of the tornado and were uninjured or had only minor injuries, and those who were severely hurt or killed.  It would have been useful to find out if the people who were severely harmed did anything differently from those who were more or less okay.  Given that at least one of the surveys was conducted via e-mail shortly after the event in question (the Tuscaloosa tornado), I would expect that there would be very few people who were severely injured who even participated in it, because they would have been in the hospital.  In effect, the social scientists gathered statistics about a control group and presented it as though it represented the experimental group.  In this situation, the statistics about behavior patterns following a warning mean nothing in themselves.  There is nothing (survival/non-survival, minor/major injury) to correlate them to.  Implying that these behaviors caused the death toll to explode is unsupported speculation.  The one survey I saw that definitely interviewed people who had lost loved ones or who were severely injured was conducted in Smithville, MS, and these authors did not make any wild inferences about how seeking out additional information had led to the deaths.  There is simply no data support for it.  The only situation where it might make a difference is when the lead time is basically zero and every second counts, which was not the case in the April 27 tornadoes or the Joplin tornado.  (I had a lead time of about 25 minutes, which was enough for me to get my cat and laptop and go 18 miles away.)

There was one data omission that is, in my perspective, more important than any behavioral survey.  One table that I did not see in any of the social science presentation was this one:

F Scale Killer Tor Fatalities
F0 1 1
F1 3 4
F2 15 24
F3 23 76
F4 13 160
F5 6 282
F? 0 0
TOTAL 61 547

(Credit to the Storm Prediction Center: http://www.spc.noaa.gov/climo/torn/fataltorn.html)

That is, 95% of all tornadic deaths this year occurred in EF-3 or higher tornadoes, which will destroy most or all walls in a house.  EF-5 tornadoes can even expose the basement and descend into it (it is a myth that the funnel would magically stop at the ground level if an open hole existed for it to twist into), sucking people to their deaths.  And it gets even more significant when you dig deeper into the data.  A look at the list at the top of that page shows that only 4 of the deaths from EF-2 or weaker tornadoes occurred in permanent houses.  I don’t know exactly what happened there, but it could have been extremely bad luck such as a tree falling on the house, a piece of heavy furniture, or a piece of timber causing injury.  It could have been a weak structure.  The point is, this is very rare.  The rest of the deaths in EF-2 and weaker tornadoes were in trailers, vehicles, outdoors (all highly dangerous places to be in a tornado) or were unknown.

I respect the research into this year’s terrible tornado casualty count.  It is important to determine exactly why this occurred, and one question that did need to be answered was whether it happened because of bad decisions.  This is the question that the social scientists have attempted to answer.  I simply disagree very strongly with their apparent conclusions, as I think they are unwarranted by the questionable research methodologies, and are little more than speculation.  My contention is that the catastrophic death toll is directly attributable to major, violent tornadoes, the kind that obliterate entire homes, happening to occur in a lot of populated areas this year.  In short, it was a statistical outlier year.  This classification does not address the underlying structural problem of the Southeast, which is that effective storm shelter is not commonly available for the most violent events, but that’s not an easy problem to resolve.  Unfortunately, in my opinion, it is this hard problem, rather than comparatively easy ones regarding bad decisions, that must be answered if this type of death toll is to be prevented from ever happening again.

August 2, 2011

Emily Organizes; Gulf Threat Decreases

Filed under: Forecasting,Tropical — Erin @ 7:42 pm

Tropical Storm Emily struggled through most of last night and today with disorganization, an aftereffect of its multivortex structure as an unnamed disturbance.  However, it has become better stacked today, with convection blowing up over its center.  It still has a long way to go, despite its more pleasing appearance in satellite photos.

Steering in the short term is straightforward.  Emily has been generally on the left side of the forecast track for most of the day, and it is now expected to make landfall in the Dominican Republic as a tropical storm.  Weaker systems generally weather the mountains better than stronger ones, provided that they do not linger in the area; therefore dissipation of the system seems comparatively unlikely.

 

Models conclude that trough will miss Emily

The models have largely converged on a scenario in which the trough that is to weaken the Bermuda High will be gone before it can force the full recurvature of Emily.  The ridge is expected to build back in, and the GFS shows the hurricane being trapped off the coast of Florida, unable to move ashore because of another ridge, stalling until a shortwave trough lifts it away.  The GFDL and HWRF models, which take their input from the GFS, both show a very close approach to the east coast of Florida, with the HWRF showing near-hurricane-force winds onshore.  The NOGAPS shows this same scenario without the stall.  In this scenario, a landfall on the Outer Banks of North Carolina occurs, followed by a pull up the Atlantic seaboard (offshore) and out to sea.

The Canadian model shows a very weak system, probably no more than a mild tropical storm, making landfall on the east coast of Florida and then being merged into the shortwave.  I should observe that the Canadian model now shows the first low strengthening to 988 mb at sea and reducing the Bermuda High to its winter stage (the Azores High), which does not seem remotely reasonable to me for an August system.  I am not putting a lot of faith in this aspect of the Canadian solution.

The European model also shows a “screwy” solution, amplifying the shortwave trough to 992 mb at sea, while completely dissipating Emily over Hispaniola.  Although unlikely in my opinion, dissipation of the tropical storm is certainly possible, as yesterday’s blog entry said, but I am having great difficulty believing that either of the baroclinic low pressure systems involved in this will reach 990 mb levels.  The first trough is currently located in New England producing a severe weather risk, and it is analyzed at 1002 mb.

Bottom line, I am giving a highly skeptical eye to anything that destroys the Bermuda High at the beginning of August and amplifies low pressure cores to winter levels, especially when they have not been doing this consistently.  Any land-free recurvature of Emily depends entirely on such “bombs,” and the approach to the East Coast will be so close that a weaker trough or shortwave will make all the difference in the world in what wind speeds are felt onshore and whether landfall occurs.

 

Gulf Coast threat decreases… for now

As should be apparent, the threat to the Gulf Coast states has decreased over the course of the day (with a caveat).  The current thinking is that the trough will lift Emily northward enough to miss an entrance into the Gulf of Mexico.  However, this could change if the storm stays south and west enough, or the trough is weaker than expected at sea.

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