U.S. Tornado Statistics and Data Set Analysis

[vortex95]

I recently asked SPC for the U.S. annual list of tornado count, fatalities, and killer tornadoes.

They sent me the list. Official records begin in 1950.

http://home.comcast.net/~trwplusa/19502011stat.pdf

This provides a good opportunity to examine an official data set and realize they can sometimes

be misleading, especially when trying to determine trends over an extended period of time.

1) There is a significant spike in annual tornado count starting in 1953. This was the year the Severe

Local Storms (SELS) unit, forerunner of SPC, was established for around the clock severe storm

monitoring. Tornado reporting was encouraged by the U.S. Weather Bureau for documentation

and watch/warning verification purposes, hence the increase in count.

2) Starting in 1990, you see another significant spike to above 1000 in tornado count. This year

marked the first installation of NEXRADs and around this time, storm chasing was beginning to ramp

up in popularity. Both of these resulted in more tornadoes being reported, verified, and documented.

3) After 1990, the NWS Modernization occurred over the next several years, and investigation of

tornado reports and post damage storm surveys at each new WFO county warning area ramped up

considerably, leading to a more representative count of tornadoes per year, staying above 1000 for

all years afterwards except 2002.

4) Storm chasing really took off after the release of the movie 'Twister' in 1996 and has continued

to grow ever since. This continued to increase/sustain higher annual tornado counts.

5) By the middle part of the first decade of the new millennium, digital cameras were rapidly replacing

traditional slide and print film. This eliminated the long processing times of film, allowing for not only

more tornadoes to be verified and documented, but also in a more timely manner.

6) By the end of the first decade of the new millennium, social media such as Facebook and Twitter

allowed instant reporting of tornadoes in real time. Wireless Internet had been firmly established for

the now ubiquitous smartphone/mobile device, combined with built-in digital still picture and

video cameras, made tornado reporting and verification even quicker and more efficient. Also,

tornadoes took front and center in the mainstream media, both in the daily news and reality shows.

So all the above shows that a data set can be misleading over an extended period of time if you

do not take into account changes in things like technology, population, and public awareness, as

three examples. Despite all this, we are still too low in the annual tornado count. By how much on

average?, difficult to say, but likely by a few hundred. We document nearly all the the significant

tornadoes, but smaller, short lived ones are missed, due to darkness, poor visibility, and/or remoteness

of location. We are finding tornadoes in the Rockies and Great Basin are more common than once

thought. Given the low population density and large area, it is likely these areas of the country are

where we miss the most tornadoes.

Some other notes...you can see the number of tornado fatalities can highly vary from year to year going

back to to 1950. Overall though, there has been downward trend in fatalities long term. However, the

benefits of better warnings and awareness/preparation is constantly being tempered by the growing

population.

Year U.S. Population

1950 151,325,798

1960 179,323,175

1970 203,211,926

1980 226,545,805

1990 248,709,873

2000 281,421,906

2010 308,745,538

We have doubled in population in 60 years. Put simply, there are just more people in the way of

tornadoes every year. In addition, population in and around the larger cities has become denser, so

the potential of very high death tolls for when a large, violent tornado plows through any of the larger

cities is becoming more and more likely as time goes on.

So I think this shows to a respectable, if not a large degree, tornadoes are only becoming "worse"

not due to meteorological or climatological reasons, but more due to technological and sociological

reasons.

Comments/opinions?

[Stebo]

I would agree with this, people are now living in areas where years prior no one lived. Locally there have been several large tornadoes in the past 60 years, if those same tornadoes hit today it would be catastrophic. The difference now, urban sprawl has occurred in the last 20 years so much so that Metro Detroit has expanded in size by vast amount. The same can be said for many metro areas across the nation.

However I do think in the last 60 years construction standards and tornado safety techniques have gotten much much better this would counteract the amount of deaths that could potentially occur even if a tornado were to come through a large city, case in point last week with the DFW metroplex.

[Hoosier]

No doubt that detection has gotten way better, but I personally think that it's possible that we are still missing up to half of the actual tornadoes that occur in the US. In other words, I think the actual annual average could be over 2000. Nothing really solid to back this up, but when you think about all the rural areas that still exist and how we know that tornadoes can be very brief, I don't think it's a huge leap. Even in more populated areas, some brief rain wrapped tornadoes may go unnoticed if embedded within a larger area of straight line wind damage.

[AtticaFanatica]

I recommend these peer-review paper about the tornado database:

http://journals.ametsoc.org/doi/full/10.1175/WAF910.1

http://journals.ametsoc.org/doi/full/10.1175/1520-0434%282002%29017%3C0354%3ADITMOC%3E2.0.CO%3B2?

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281988%29116%3C0495%3AOSIOUS%3E2.0.CO%3B2

Also, I think weak tornadoes without condensation funnels also may impact the climatology in some measurable way.