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Measuring tornadoes: F-scale vs. EF-scale


Natalie Thomas, reporter
April 3, 2012 — When it comes to measuring tornadoes, in Canada we use the Fujita or F-scale. In the United States, the Enhanced Fujita or EF-scale is the norm. Natalie Thomas finds out the difference.


When it comes to damage, there are still some improvements that need to be made to the EF-scale
When it comes to damage, there are still some improvements that need to be made to the EF-scale

While the F-scale has been in use in Canada for a number of years, Dr. David Sills with Environment Canada says they hope to implement the EF-scale in 2013.

"The problem with the Fujita scale is that the winds that are associated with the damage weren’t very well correlated, as far as engineering studies go," explains Sills. "The wind speeds at the high end were too high, and the wind speeds at the low end were too low. So the purpose of the EF-scale is to try to get a better correlation between the wind damage and the wind speeds."

Sills says that last year, Environment Canada did a parallel test of both the F-scale and EF-scale using different damage from different tornadoes. "We noted some differences and a lot of similarities in the rating systems," he noted.

Sills says that even the EF-scale needs to evolve, especially when it comes to trees and certain buildings like the ones we have here in Canada. Last year's F-3 tornado that tore through Goderich, Ont. is a good example.

Environment Canada hopes to implement the EF-scale by next year
Environment Canada hopes to implement the EF-scale by next year

"In Goderich we had a lot of buildings that were downtown, kind of heritage buildings that were solid brick structures," he says, "and when those are significantly or severely damaged we call that an F3 on our scale that we use in Canada."

But Sills says that that kind of damage and building structure isn't really worked into the EF-scale yet, so the most you can get out of that kind of damage from the EF-scale is an EF-2.

"So these are the kinds of things that need to be improved in order for the EF-scale to be brought into Canada," he says. "It has to cover these kinds of buildings and the kinds of structures that we have here in Canada and may not be covered so well in the States."

Sills also says that there is hope to eventually have a scale that is constantly evolving. "I'm actually in a group of scientists that are in the United States and Canada that are trying to suggest improvements to the EF-scale to make it a better scale -- more representative and more consistent."

Environment Canada hopes to have the Enhanced Fujita scale implemented in Canada next year.

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