----- Original Message ----- From: "Kevin Tarr" <[EMAIL PROTECTED]> To: "Brin-L" <[EMAIL PROTECTED]> Sent: Sunday, April 21, 2002 11:57 PM Subject: Re: Tornados
> > > >From the weather geek in me: the Fujita-Pearson Scale is based on > damage > > > done to man-made structures. A super strong tornado in the Mississippi > > delta > > > that destroys nothing valuable could be a F0, while a moderate tornado > > that > > > by chance, as in it never moves more than a few feet for some minutes > but > > > completely destroys two houses, could be a F5. > > > > How sure are you of this. Everything I've read, including the web site > you > > furnished, gives the F number in terms of the maximum wind speed. I've > been > > following meteorology ever since I took near daily breaks from my > dissertation > > and walked over to the UW meteorology building to look at the weather maps > > back in the late '70s and early '80s. > > > > > > > > > This we site compares death rates vs. scale and all tornadoes from > 1950 - > > > 1994. > > > > > > http://www.tornadoproject.com/fscale/fscale.htm > > > > > > Kevin T. > > >From the web page: > > The Fujita Scale is based on damage, not the appearance of the funnel. > > The Seymour, Texas, tornado of April 10, 1979 is a prime example of a > tornado that is destined to be misjudged on the Fujita Scale. This > spectacular funnel was probably capable of F4 damage, had it passed through > a town. It produced only telephone pole and tree damage, and thus could be > rated no higher than F2 damage. > > Me: It's giving the wind speed as an indication of what damage could happen. > I am just pointing out that a 315 MPH tornado that damages nothing will be > classified as a F0. Actually, its the other way around. Look at how precise the wind speed definition is. The description of damage, on the other hand is qualitative. The wind speed can be determined by an engineering analysis of the destruction. If the not enough about the structures is known, then one cannot make a good estimate. From the text it appears that they, quite reasonably, are conservative in assigning higher Fujita numbers. Thus, if the damage is to unknown structures, the intensity could very well be underestimated. This is why the word "misjudged" is used in your quote. >I know of tornadoes that ripped up cornfields, causing a > lot of crop damage, but were F0 because they didn't damage anything > man-made. They don't have to damage anything man made. If that were the criterion, then the scale would be in terms of dollars or lives. Instead it is precisely given in terms of wind speed. I know that the F5 tornado in Oklahoma was within 1 mph of being an F6. If there is a good Doppler radar reading of wind speeds, then that is also acceptable to determine the Fijuta number. I realize that using Doppler radar is fairly recent and that the origonal scale was based on damage. But, the goal of Fijuta was to measure intensity given data that would be available at the time. It is more likely for an intense tornado that goes through a big city to be accurately measured because better data are available. If there was a way to obtain good data elsewhere, then that would suffice. Dan M.
