• Stephen M. Strader

Where Have All the Violent Tornadoes Gone?.... Hint: Nowhere

Updated: Dec 30, 2018

Over the last week there have been a number of press pieces (See end of post) discussing how this will be the first year without any “violent” tornadoes in the United States. I have also seen a number of tweets aimed at discussing the reason for the lack of violent tornadoes this year. While I understand that many times it can be hard to get across your point to the media, I think there are quite a few issues about violent tornadoes not being discussed or simply overlooked. This posts highlights some important things to consider before reading TOO MUCH into the lack of “violent” tornadoes this year.

Points of Clarity for the General Public

  • Tornadoes are rated based on the amount of damage they cause of specific structures. There exists a database of laboratory measured/tested damage that occurs to building materials at specific wind speeds. These materials are referred to as damage indicators (DI). The amount of damage is called the degree of damage (DOD). Wind speeds in the tornado are inferred from the DOD to the DIs. https://www.weather.gov/oun/efscale

  • Tornadoes are rated 0 to 5 on the Enhanced Fujita (EF) scale.

  • Violent tornadoes are those tornadoes rated EF4 and greater with winds of 166-200+mph.

My Opinions: Things Being Forgotten or Overlooked

1. No, this is not the first year in the U.S. without violent tornadoes.... It is only the first year on record.... Tornadoes were here long before humans and will be long after we are all gone. Besides, there are a number of issues with the tornado database that I won't go into here..... okay... I briefly do...

2. I’m not even sure what violent means to anyone but me…. Now, of course I know more about this than the average person because I have studied tornadoes for the last decade….. But what does violent mean to the general public? For example, try to go tell someone that had their home destroyed by a tornado that it’s going to be okay because they only had EF3 damage, it wasn’t violent after all. This just points to the fickleness of language associated with tornado ratings and how it can be very confusing to the general public. How people internalize words like “violent” or “significant” as it relates to tornadoes is incredibly important. Social scientists and meteorologists are just now (last 15 years) starting to work together to learn how language affects how people perceive and respond to severe weather threats. We have to be careful when using words like violent.

3. Violent tornado "drought".... Where to begin with this one. It's not a drought... First off, using the term drought in this context is confusing to the general public. People may get that confused with lack of precipitation. Second, we just got over a hurricane "drought" and it left us with record breaking rainfall, devastated communities, and billion dollar losses. These long pauses in events often leads to complacency bias that exacerbates disaster when the next event does occur. Let's hope this doesn't happen with pitching the downward trend in violent tornadoes to the media....

4. Trusting tornado ratings pre-1970s is a bad idea. These events were rarely surveyed in person and most of the ratings for these tornadoes were assigned by graduate students reading newspapers, looking at photos, and reading eye witness accounts. I don’t think I need to go into how many biases and issues this can create…..

5. Violent tornadoes are rare. Period. They are rare events that take a combination of factors aligning to occur. We are not talking about hundreds of events a year, but rather a handful of tornadoes (less than 10 on average) that create some type of damage that is related to EF4 or EF5 wind speeds. Thus, it is not entirely impossible to end a year with zero violent tornadoes….. which brings me to my next point.

6. How tornadoes are surveyed and rated is EXTREMELY biased and subject to TREMENDOUS variability/error. First off, rating tornado intensity is not an exact science most of the time. There is a lot of grey area and subjective surveyor input that goes into determining whether the damage to a structure is consistent with high-end EF2 or low-end EF3, high-end EF3 or low-end EF4, etc. Many times there are lines in the sand being drawn depending on who surveys the damage, the thoroughness of their survey, their experience with the event (e.g., the same people issuing the tornado warnings are responsible with surveying and rating the tornadoes ….. I won’t get into this issue right now), etc. Moreover, National Weather Service (NWS) employees that are tasked with rating tornadoes have very limited time and personnel to spend on surveying the damage given their resources are often stretched very thin. All of this leads to some degree of uncertainty. Now, do not get me wrong, it is not an easy task to survey tornadoes and get it 100% right. There also does not exist a better method out there for surveying tornado damage given resources and technology. However, I am just pointing out the HIGH amount of uncertainty in the tornado damage rating process. So, to put so much weight on whether an EF4+ tornado occurred this year is somewhat meaningless given the above mentioned. After all, humans are indeed the ones conducting the damage surveys and we are extremely biased beings that subconsciously search for patterns. We can't be 100% objective!

7. It only takes one damage indicator (DI) at EF4+ to rate a tornado as “violent”. This means a tornado can traverse hundreds of miles across the ground causing only EF0 damage, but if it just so happens to create EF4+ damage in ONE location, it will be rated as a violent tornado. This seems a bit biased to me. Nevertheless……

8. Tornadoes are not points….. They are areal phenomena that vary across geographic space (i.e., that are chaotic and ever-changing). Therefore, assessing tornado intensity with point estimates of damage is a major source of error. There is no way to even remotely account for the high amount of wind speed magnitude and spatial variability within a tornado. For example, take 2013 El Reno, OK tornado. This tornado is the widest tornado in recorded history and by all accounts an extremely violent event. Yet, there was much debate about what magnitude the tornado should be rated at due to conflicting data. This debate made national news and has highlighted some issues with our current tornado intensity rating system (see https://news.nationalgeographic.com/news/2013/10/131024-tornado-el-reno-oklahoma-samaras-enhanced-fujita-scale/. Without diving too deep into it, the issue stemmed from surveyors trying their best to rate the tornado within the guidelines of the Enhanced Fujita scale. This directly conflicted with the mobile Doppler radar data collected just a few meters off the ground. Thus, there was confusion about how to classify the tornado.

Overall, tornadoes are constantly changing, dynamic entities. The damage that they create in one location does not always equate to the same amount of damage even right across the street. Tornadoes do not care about fitting into our Enhanced Fujita scale molds, nor does the damage that they cause always fit nicely into our understanding of the relationship between wind speed and damage to a structure. Thus, in my opinion, it seems very silly to get caught up in the rating of these events given the known issues.

2013 El Reno tornado damage survey points

9. Another HUGE issue with rating tornadoes is the DI bias. DI bias occurs when a tornado traverses a largely rural landscape with few DIs, leading to an often lower damage rating on the EF scale. Simply put, the tornado didn’t hit anything that can be used to estimate its wind speed. So, it goes into the database as best as possible…..This issue was first addressed by studies from Schaefer, Doswell, Burgess, Brooks, etc. from the late 1980s to the late 2000s. A paper of mine that came out in 2015 (https://docs.wixstatic.com/ugd/fc36a1_796c14da18ae4a819541fd31d4fd016e.pdf) also highlighted this issue from a geospatial land use stand point. Overall, if a tornado doesn’t cross over a developed landscape, there is a MUCH lower chance of it being rated significant (EF2+) or violent (EF4+). The rating then is often left up to chance!

From Strader et al. 2015; Meteorological Applications

Highlighting this issue further, let’s take the May 1, 2018 tornado that occurred just northwest of Salina, KS. This tornado was on the ground for 14.5 miles and was ½ mile wide. It was also a heavily chased tornado with many photos indicating that it was a substantial tornado capable of conducting significant damage. Nevertheless, the tornado was rated an EF3 tornado based on 36 survey points. Of these 36 points, all 11 of the EF3 DIs were associated with one structure (see below). A majority of the time the tornado was on the ground it was traveling through undeveloped cropland and pasture. It struck very few DIs. My point isn’t to knock those who conducted the survey, but to point out how easily the tornado could have been rated violent had it struck a small community or subdivision. What if that tornado had occurred 15 miles to the southeast and ran through the heart of Salina, KS? Or, what if it had just occurred three miles to the northeast and struck the community of Minneapolis, KS? (see image below) It is very likely that this event would have been rated a violent tornado considering it only takes ONE EF4+ DI to rate it a violent tornado. Then, we wouldn’t be talking about the year without a violent tornado. The point is that there is always an element of luck involved with tornadoes and too much can be read into the rating of these events.

11 EF3 survey points with 1 EF2, 3 EF1, and 3 EF0

May 1, 2018 tornado and land use

…. Besides.... Just imagine if the El Reno tornado would have happened 50 miles east and gone through the heart of downtown Oklahoma City….

10. We have been lucky with tornadoes. Singular hail storms (often supercells capable of producing tornadoes as well) have far surpassed damages from all but a handful of tornadoes in history. And these types of hail events seem to be increasing over time https://www.washingtonpost.com/news/capital-weather-gang/wp/2018/08/08/costly-hailstorms-are-rapidly-increasing-heres-what-the-weather-community-is-doing-about-it/?utm_term=.9becb94ce3e3. There were many of these hail events this past year in Texas and Colorado. It’s only a matter of time before one of these storms puts down a tornado along with the hail, leading to violent damage in highly populated city.

11. As I just mentioned, it is only a matter of time….. We are loading the disaster dice year after year waiting for a tornado to do unimaginable damage. Less we forget, we are only 7 years removed from the Joplin, MO EF5 tornado that killed 150+ people. What if an event like that had gone through downtown Dallas-Fort Worth? St. Louis? Chicago? Etc. My work, along with others, has indicated that if we keep building across the landscape year after year, tornado impacts and disaster likelihood will increase. Thus, IN MY EDUCATED OPINION, the downward trend in violent tornadoes is a distraction from what the future holds. This is the heart of the expanding bull's eye concept I have been working on over the last 7 years. See this link for all expanding bull's eye work (http://chubasco.niu.edu/ebe.htm).

What is the expanding bull's eye effect? “Targets”—i.e., humans and their possessions—of geophysical hazards are enlarging as populations grow and spread. It is not solely the population magnitude that is important in creating disaster potential, it is how the population and built environment are distributed across the landscape that defines how the fundamental components of risk and vulnerability are realized in a disaster. ​ Why is it important? While climate change may amplify the risk of certain hazards, the root cause of escalating disasters is not necessarily event frequency, or risk, related. Rather, our recent research confirms the upward trend in disasters is predicated on increasing exposure and vulnerability of populations (http://chubasco.niu.edu/ebe.htm).

Overall, this post isn’t trying to take shots at the effects of climate change on severe weather, statistics, etc. I believe that climate change is playing and has played a role in tornado events for quite some time now. However, I’m not sure to what extent it is playing and whether or not these effects aren’t just being overshadowed by more important factors such as societal vulnerability and exposure. Nevertheless, we are just now getting around to making our best guesses about what the future holds for tornadoes and climate change. We should be careful to jump to conclusion. Besides, the same mitigation strategies we can apply to combating climate change also mitigates other factors that influence disaster magnitude and frequency. Promoting these ideals is a win-win.

What I do know is that people should not get caught up too much on the trends in violent tornadoes or specifically 2018 not having any violent events. As I have illustrated, it is a complex issue and there are MANY, MANY, MANY factors that could lead us to a lack of violent tornado events. They range from environmental conditions to simply chance. We have to be careful to not let our guard down with future tornado events. It’s a deadly game to assume that violent tornadoes will be a thing of the past. It only takes one event to change the narrative. Developed land area is increasing, the number of people and homes are increasing, the amount of “stuff” people have is increasing, our environment is changing, and the gap between the wealthy and poor is growing. This is a recipe for future disasters. It is only a matter of time.

By @StephenMStrader

Washington Post - https://www.washingtonpost.com/weather/2018/12/26/will-be-first-year-with-no-violent-tornadoes-united-states/?utm_term=.a5865103be1a

USA Today - https://www.usatoday.com/story/news/nation/2018/12/28/tornadoes-set-record-lows-2018-only-10-deaths-us/2431360002/

© Stephen M. Strader 2018

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