“Tornadoes”. “Swarms”: Words We Don’t Like to See Together

October 17, 2014

Terrorists. Oil revenue.

Ebola. Cruise Ship.

Tornadoes. Swarms.

Lindsay Abrams in Salon:

A new study, published Thursday in the journal Science, is the latest to indicate that tornadoes have been acting differently lately. NOAA researchers looked at U.S. storms going back to 1954, and found that the number of “tornado days” (days during which a tornado occurs) has declined since the 1970s. Since the total number is remaining steady, that means that tornado days are rarer but also more eventful. In 2011, for example, there were only 110 tornado days, down from the 1970s average of 150 — but nine of those days saw more than 30 tornados each. One horrific two-day stretch saw 175 confirmed twisters.

The study also finds that tornado season has been occurring erratically: while the heaviest activity usually begins in March and April, things are now getting started both extremely early or extremely late, depending on the year.

The changes have practical implications, as insurers and emergency responders need to anticipate less frequent, but potentially more damaging, tornado disasters. As Harold Brooks, the study’s lead author, told Science magazine, “We need more resources … even if we don’t use them very often.”

The money question, of course, is whether or not this is our fault. The atmosphere has certainly been changing since the 1970s, warming as a result of greenhouse gas pollution. But while the researchers don’t think the changes they observed stem from a reporting problem, they say it’s too soon to draw a link between climate change and tornadoes gone wild. “We know that tornadoes form when there is lots of energy available for thunderstorms and when there is lots of wind shear,” Brooks told Smithsonian Mag, noting that while the former is increased by global warming (heat = energy), the latter is expected to decrease.

MSN: News:

Brooks’ team logged an increase of as much as six times in days with multiple tornadoes. In the ’60s and ’70s, there was 0.5 to one day each year with more than 30 tornadoes ranking above EF-1; in the past decade, that number has shot up to three days. The last year to feature less than two days with under 30 twisters was way back in 2002. Here’s more from the study:

In effect, there is a lower probability of a day having a tornado, but if a day does have a tornado, there is a much higher chance of having many tornadoes. As a result, tornadoes are “concentrated” into a smaller number of days in more recent years. Approximately 20 percent of the annual tornadoes in the most recent decade have occurred on the three “biggest” days of each year, in contrast to 10 percent in the earlier period. This concentration leads to the potential for short periods of time, such as months, to have extreme (both large and small) numbers of tornadoes.

5 Responses to ““Tornadoes”. “Swarms”: Words We Don’t Like to See Together”


  1. […] Terrorists. Oil revenue. Ebola. Cruise Ship. Tornadoes. Swarms. Lindsay Abrams in Salon: A new study, published Thursday in the journal Science, is the latest to indicate that tornadoes have been a…  […]

  2. climatebob Says:

    The increase in the power of tornado’s is a worry but I have just been looking at bursts of rain within a rain storm. http://www.climateoutcome.kiwi.nz/increased-flood-damage-in-a-warming-world.html


  3. I have not done any statistics but it seams tornadoes are much more common in some years and less common in other years. So we now get tornado years.

  4. Gingerbaker Says:

    Swarms of tornados? – bad. Swarms of Japanese giant hornets? – Worse.

    • dumboldguy Says:

      Don’t forget the swarms of brain-eating amoebas, Rocky Mountain Pine Beetles, the ticks that are decimating the moose in MN and NH, and all the other scourges that are moving ever northward because of AGW….

      (that includes the oilfield workers from TX that are now in ND)


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