The EF Scale and Asphalt Scouring Caused by the March 2 Henryville Tornado

[Bob Hartig]

I should clarify that the original F-scale was designed to connect the Beaufort scale to the mach scale, which is where the F6-F12 designations came from. So I suppose it technically was also a wind scale, but I think the meaning of the scale has been lost between then and now.

Yeah, that's how it started out, and then it got limited to F5. F6 was a theoretical possibility if you went by wind speeds, but once the damage function of the scale got emphasized, F6 became meaningless because it dealt with purely hypothetical winds for which the damage yardstick didn't exist (having been blown away entirely at F5). I initially thought of the scale as Ted Fujita's attempt to extrapolate wind speeds from damage, but eventually I got it hammered home that it was a damage rating only, nothing more, though I suppose someone should have informed the good doctor as well, because he didn't seem to have been aware of that fact when he designed the scale.

Now we've got the EF Scale and we're using Doppler radar in some cases to help determine ratings, and part of the scale's premise in the first place was to more accurately correlate damage with wind speeds. To my mind, this Scale has suffered from identity issues for a long, long time, and if I think about it too much, I get a headache. Thankfully, far more astute minds than mine continue to work through the scale's imperfections and complexities with an eye on increasing its usefulness. But I'll bet even those guys are popping their share of Advil.

 

[Shawn Schuman]

I've always thought that the EF scale was just applied to building/structure damage.

Mostly, yes. Trees are officially included as well. But buildings can't always tell the whole story if there aren't sufficiently well-built structures in the path of the tornado, so sometimes consideration is given to things that aren't officially part of the scale. I don't know how much weight they're given, but it would seem they can be strongly considered given several tornadoes have been rated EF5 largely on the strength of unconventional damage.