April 1, 2015

Counting Storm Shelters Along the Highway

Filed under: Severe — Erin @ 12:54 am

Not long ago, during spring break, I went to Huntsville, Alabama with family on a quick getaway.  We’d had a harsh three weeks of winter conditions in an area that is unaccustomed to them, and which is certainly unaccustomed to four winter storms in about twenty days.  We were also under assorted conditions of stress from work, school, and preparation for the future.  We needed the trip, short though it would have to be.

No one in the car really wanted to drive on I-20/I-59.  That stretch of interstate between Tuscaloosa and Birmingham is incredibly nerve-wracking and dangerous, and is not something I’d recommend to any driver unless one particularly savors the thrill of bumper-to-bumper 75 mph across three to four lanes and people passing with only feet to spare.  We took the state highways instead.  Some of the drive took place on Highway 43, a winding but generally pleasant stretch of road that passes through such Alabama towns as Hamilton and Hackleburg.

It was as we approached Hackleburg that we saw the first unusual scene:  a swath of trees snapped, long denuded of leaves, bent down flush with the ground at assorted angles.  The realization hit all of us at once.

The track of the EF-5 “Hackleburg tornado” (really an extremely long-tracked tornado that began in far western Alabama and continued a little into Tennessee) paralleled Highway 43 early in its lifespan, and EF-5 damage was observed along this part of the path.  The destruction we saw was not the organized logging of a timber company.  They weren’t even the type of trees likely to be felled for commercial purposes.

It has been almost four years, and yet these downed trees still remain, a stark reminder of the violence of April 27, 2011.

We continued our drive.  As we moved into Hackleburg, we saw the first one along the road.  A heavy, inset, but otherwise unassuming rectangular door that opened into what appeared to be a small room built into a slope on the property.

“Storm cellar,” somebody remarked matter-of-factly, with no alteration of tone or pitch.  It might have been me.  I don’t recall who noticed the first one.  We were all pointing them out before the end of it.

The “Hackleburg tornado” took 72 lives in rural and small-town Alabama, scouring 132 miles with its fury.  The official survey claims that the winds were at least 210 mph.  I am convinced that they were much higher than that in places.

We talked about things we remembered about this tornado.  I was pretty sure that it had created a “situation” at the nuclear power plant in northern Alabama.  It had.

“Storm cellar.  Looks like the same kind as before.”  And indeed the second one we noticed did look like the same design as the first one.

Although they are generally acceptable for shelter in most tornadoes, I am firmly of the opinion that basements and above-ground safe rooms (even reinforced) are insufficient to guarantee safety in EF-5 tornadoes.  There have been basement fatalities before.  I particularly recall that they happened in the 2008 Parkersburg, IA EF-5 tornado.  Think about it:  If a basement is even partially above surface level, or the flooring above it is not specially reinforced, then just what exactly is to prevent an EF-5 tornado (capable of leveling a house down to a bare slab foundation) from exposing a basement and then descending into it?  If a safe room is above-ground, what is to prevent an EF-5 tornado (capable of hurling heavy metal tanks up to a mile, as happened in the 2013 Moore, OK tornado) from tossing a massive object right at it and crushing it?

“There’s another storm cellar.”  Again the same type.  Most likely the same contractor installed them.

I have some misgivings about the notion of building earthen walls around prefabricated storm shelters, particularly those plastic rooms that Southeasterners frequently saw advertised after the 2011 tornadoes.  The tornado that I drove away from that day, the EF-5 Kemper/Neshoba tornado, dug trenches into the ground 2 feet deep.  The storm shelters that we saw along Highway 43, however, appeared to have been built into natural embankments.  I hope they are sufficiently deep into the ground that they could not likely be exposed by another monster of that sort.

“Another storm cellar.”

We were all pleased to see the residents of Hackleburg being prepared.  It must have been an unimaginably traumatic event.  I didn’t even lose anything, but merely the fear/expectation that I was going to lose everything left me with a mild case of PTSD-like symptoms every time the anniversary approached.  In order to be sure of this, I would have to make the drive again with someone marking placing markers on a GPS-enabled map whenever we passed a house with a shelter, but it is even possible that these were all people who lost their homes in the 2011 tornado.  They were certainly close to the EF-5 damage path, if not directly in it.

These appeared to be homes of middle-class residents.  It should be easier for everyone to install a—

“Storm cellar.”

By then we were simply saying the words.  It was almost like another road game, such as counting cars of a particular color.  As we passed through Hackleburg proper, we couldn’t help but observe how much construction appeared to be quite new.  Even the road had a new stretch of pavement, identifiable because of its smoother surface and different, darker color from the surrounding road.  The tornado did tear up the asphalt as well.  Intense tornadoes often do that.

“Storm cellar.”

If this stretch of road is representative of the community, that says something very positive about the residents of this area.  I don’t support unfunded mandates to require private homeowners to have basements or storm shelters, because I think people should have the right to face private, personal risk as they see fit (after all, I did precisely that by choosing to hit the road to evade an EF-5 tornado, against the recommendation of the National Weather Service), but I am very glad when people do take the initiative to protect themselves and their families in this manner.  I am in favor of the “carrot” of permanent tax credits for any expenditure of this nature.

There were six homes with the same kind of earthen, in-ground storm cellar just along Highway 43 between Hamilton and Hackleburg.  I’ve never seen that many in such a small area before.  It might not even be noticed by most people, especially people who did not know that an exceptionally violent tornado had occurred in this place four years earlier.  But those of us who did have that bit of knowledge, and who still look at things outside the vehicle instead of some sort of onboard entertainment, noticed this series of doors opening to rooms in the ground.  It was a subtle indicator of something different about this area.

Trauma changes people.  What we saw that day, March 11, 2015, was proof positive that it changes communities too.

September 1, 2013

For the Record

Filed under: Severe — Erin @ 7:06 pm

The El Reno tornado (2013) was, in the official records, downgraded from EF-5 to EF-3 on the basis that EF-5 damage was not found and “the Enhanced Fujita scale is a damage scale” (quotation my own).  Let me go on record right now as saying that I oppose this and all other instances where scientifically collected, calibrated wind speed data are ignored.  I oppose the practice of rating tornadoes based strictly on those factors that civil engineers deem important while throwing out data collected by meteorologists, and for several reasons.

  1. Estimates of wind speed that are derived ex post facto from damage are inherently less reliable than objective, instrumentally collected measurements.  This should not even be controversial.  Differences in materials, building practices (which can be very hard to determine in the event of total obliteration), and even environmental factors (e.g., temperature and humidity) prior to a tornado can affect at what wind speed the structure fails.  Surveys attempt to find out about such things, but it’s inherently impossible to cover all bases.  Measurements are always more reliable than estimates, even educated ones.
  2. The Enhanced Fujita scale was designed to be expanded.  In practice, vehicular and ground damage are now included as damage indicators in surveys, even though the official EF scale documents don’t (to my knowledge) list them.  There was also the intention, when the scale was formed, of leaving it open for actual wind data to be used in ratings.
  3. The Enhanced Fujita scale is a wind scale.  It is not just a way of rating the intensity of damage, which need not have anything to do with wind at all.  The EF scale is not used for rating damage caused by floods, hailstorms, or earthquakes; it is used for tornadoes, which are wind events.  Tornado surveys do not merely say that a tornado “has produced EF-3 damage.”  They also assign an estimated numerical wind speed to the storm.  This is apparently a subtle point for those who insist that the EF scale is a “damage scale,” but I really don’t think it’s all that hard to understand once you think about it.  Saying that the EF scale is a damage scale is like saying that, traditionally, the Celsius scale was a mercury expansion scale, not a temperature scale, because mercury thermometers were used to determine temperature.  That would obviously be ridiculous.  The EF scale is a wind scale.  Primarily it uses damage for the determination of wind speeds, but only because measurement data are not usually gathered.  That unfortunate circumstance is no reason to throw out valid data when they are available.
  4. Portable Doppler wind measurements can, in fact, be extrapolated to the surface in tornadoes.  The wind speeds near the ground level (i.e., damage level) of a tornado are likely to either match or even exceed those found at heights measured by portable Doppler radar (Wurman et al, Bulletin of the AMS, June 2013).  Though the researchers cited didn’t measure a tornado with winds this high, the research implies that, yes, 300 mph winds could occur at the surface if they were measured at portable Doppler level.  The cited research is another reason why I have gotten off the fence and decided that 320 mph or higher winds could also theoretically occur at the surface in subvortices of the most violent tornadoes, such as, perhaps, the Hackleburg, AL tornado of 4/27/2011.

It is becoming increasingly clear to meteorologists that, although the categories of the EF scale are probably accurate as regards the intensity of wind required to damage structures in specific ways, the scale is grossly inadequate for measuring the highest possible winds that a tornado could produce.  There is little question that the most powerful EF-5 tornadoes can generate winds well in excess of 200-210 mph at the surface, especially if they are multivortex.  Surface winds of 300 mph in subvortices are also a near-definite, and there is quite a difference between 210 and 310 mph.  The former will reduce a well-built house to its foundation but could be survivable; there are accounts of people who sat through Category 5 hurricanes, which could generate wind gusts of that intensity.  The latter will shred the debris into pellets and tear the human body to pieces (see, for example, the Jarrell, TX tornado of 1997, but get your Pepto and smelling salts if you read detailed accounts of that).  The former could be ridden out in an above-ground shelter (the kind of shelter, incidentally, that some non-meteorologists involved in the creation of the EF scale had a financial stake in selling—just saying).  The latter requires an in-ground storm cellar with guard rails to hold.  I regard it as, frankly, grossly irresponsible for the public not to be informed of the true intensity that EF-5 tornadoes can reach or what such incredible winds can do.

I don’t blame the meteorologists at Norman for what happened.  They wanted to use hard data in the rating of the El Reno tornado, obviously.  There must have been pressure exerted from some other source.  I do hope, however, that weather scientists are soon able to force an official change in the procedure of rating tornadoes when calibrated, scientifically valid wind data are available.  One way to bring this change about more quickly is to increase funding for university meteorology departments so that they can send out chase teams equipped with portable Doppler.  Disregarding one or two sets of data, all from one small region, can apparently be done by the “powers that be.”  Disregarding data from all over Tornado Alley might not be doable.

June 7, 2013

Thoughts on Instrumental Measurements in Tornado Ratings

Filed under: Severe — Erin @ 10:32 pm

It’s been a while since I blogged anything.  I’ve decided that I do not really want to be a forecaster, but instead, a research meteorologist, and the war for funding is so intense that I’d much rather publish research in a scientific journal than on my blog.  However, this post is not research; it is commentary and speculation.  The opinions in it are no one’s but my own.

A controversy in meteorology has developed about the use of mobile Doppler wind data to rate tornadoes.  It flared up initially in 2011 when a tornado in El Reno, OK was rated EF5 purportedly because of mobile Doppler measurements.  However, it later came to light that the tornado had produced EF5 damage indicators along its path as well, including the hurling of very heavy oil tankers, the moving of equipment weighing a million pounds, and the intense scouring of dirt.  The controversy has arisen again, though.  At least two tornadoes in May 2013 had their ratings increased (rather significantly, I should add) strictly because of wind measurements.  The May 31 El Reno, OK tornado was increased from EF3 (from damage indicators) to EF5 because of a mobile Doppler measurement of 296 mph at 500 feet above ground level.  The Rozel, KS tornado was increased from EF2 to EF4 because of a wind measurement.

Some people seriously object to the use of instrumental readings in tornado ratings.  “The EF scale is a damage scale!” they say.  And, to an extent, it is.  However, that’s not all that it is.  In surveys, tornadoes are not simply said to have produced damage of a particular category.  Attached to each of the six ratings is a range of wind speeds that were determined, via engineering analysis, to produce such damage.  Surveys include an estimate of the wind speed of the tornado as well, and these wind speed estimates are often very specific.  I have seen surveys of EF4 tornadoes, for example, that distinguish between 170 and 190 mph winds.  Since the EF scale does not simply classify the level of damage produced by the tornado, but also includes numerical wind speeds for the tornado itself, I therefore have to come down on the side of those who use mobile Doppler and other calibrated, accurate forms of measurement to rate tornadoes.

However, there is a caveat.  I’m concerned about the use of mobile Doppler in areas like the Oklahoma City metro area resulting in a skewed picture of the distribution of EF4 and EF5 tornadoes.  They also are documented in areas that don’t happen to house the Storm Prediction Center, University of Oklahoma meteorology department, Norman OK National Weather Service Office, and National Severe Storms Laboratory.  However, if measurements of these tornadoes are never taken because of a lack of resources, they can be misrated.  The May 31 El Reno tornado was initially rated an EF3 from damage.  One cannot help but wonder how many tornadoes outside this Mecca of meteorology are misrated because there may not be a massive pool of storm chasers with state-of-the-art instruments.  Nevertheless, the proper course of action to correct for this is to fund more tornado research and wind-measuring equipment, not to sacrifice scientific accuracy on those occasions when we can obtain it.

The 296-mph winds in the El Reno tornado (at 500 ft.) were detected in a mesovortex.  This fact would also explain why, perhaps, some tornadoes are underrated; such small vortices might not strike anything if the path of the tornado is primarily unpopulated.  The outer funnel of the El Reno tornado had winds in the EF4 range, though again, at 500 feet.  Winds at the surface in the outer funnel may in fact have only been in the EF3 range, as the damage indicated.  However, this brings up several interesting points.

First, some meteorologists objected to the EF scale because they knew that the winds in EF5 tornadoes could reach speeds much faster than 200-210 mph, the range given in every damage survey for an EF5 tornado until the Joplin tornado.  They knew it from hard observations, including the mobile Doppler measurement of 300 +- 20 mph in the Bridge Creek tornado of 1999 and a measurement of 284 mph in the Red Rock tornado.  Now it seems that this was not just a pair of flukes; such extreme wind speeds may occur much more frequently in multivortex tornadoes than previously imagined, and not just those officially rated EF5.  The Red Rock tornado was rated F4 rather than F5 because wind measurements did not count in the old Fujita scale, and the 2013 El Reno tornado apparently didn’t produce demonstrable EF5 damage.

Second, I would bet that the usage of the EF scale, however accurate it is for below-EF5 winds, has resulted in some extremely inaccurate official wind estimates for EF5 tornadoes in surveys.  210 mph for the Smithville, MS and Hackleburg, AL tornadoes?  I do not believe that for a minute.  Now, I know that it is apparently not possible to distinguish between 200 and 250 mph on residential home damage alone, but if that much uncertainty exists, and if we know that tornadoes do indeed produce 250 mph winds at times, then I think damage surveys should not attempt to estimate a precise wind speed for an EF5 tornado from damage.  To do so implies a level of accuracy and surety that does not actually exist.

Finally, it is worth noting again that the 2013 El Reno tornado did not, apparently, produce demonstrable EF5 wind speeds in its outer funnel or its damage path, but a mesovortex inside the tornado nevertheless reached 296 mph.  This raises some serious questions about just how strong those mesovortices can become.  Now, many damage surveys for EF5 tornadoes note that the swath of EF5 damage was very small, a fact that indicates a mesovortex as the probable culprit.  One can be particularly confident in this if video exists of multiple vortices and the tornado’s path crossed over a developed area, as was tragically the case for the 2013 Moore, OK tornado.  However, what does that suggest for tornadoes that do produce wide swaths of EF5 damage along their paths, swaths too large to have been created by transient mesovortices and that were probably generated by the main funnel itself?  If the El Reno tornado generated an inner vortex spinning 110 mph faster than its main funnel, then I would be inclined to say that some multivortex (E)F5s that were rated on damage may in fact have generated “F6″-range winds (319+ mph) in their inner vortices.  (I say this with some trepidation, because there are few things more controversial and inflammatory in severe storms meteorology than the use of the term “F6.”)  I’m looking at the Hackleburg-Phil Campbell tornado and the Kemper-Philadelphia tornado (both of the April 27, 2011 super outbreak) in particular for this.  The former tornado had an uncommonly large path of EF5 damage, indicating that the main funnel may have reached EF5 levels; the latter had a small region in which the dirt was dug out of the ground to a depth of 2 feet, indicating the possibility of an inner vortex of truly incredible intensity.

I’ve personally been on the fence for a long time about whether such winds can occur on Earth–but this information about the El Reno tornado is edging me off that fence.  I doubt it could happen very often, of course.  I’m not suggesting that every EF4 or EF5 tornado is harboring an inner funnel with 330 mph winds at the surface.  This most assuredly is not the case.  Most EF5s earn their ratings not because of an EF5 damage swath attributable to the outer funnel, but because they do tend to be multivortex, and something had the misfortune of being struck by an inner vortex with EF5 winds.  But do I think 319+ mph winds could occur in a tornado that did have EF5 winds in its outer funnel?  Do I think they may have occurred before?  Honestly, at this point, I’m inclined to give a tentative yes.

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