I wonder what it was about the obliterated houses that differentiated them from the standard F5 obliterated house - I would like to see a bit more detailed report that describes the structural issues surrounding the final decision.
Happened several times this year -- the Harper F4 comes to mind right away. The house was completely leveled, with no structure remaining that was above-ground. However, I'm assuming two things here that kept the rating at F4:
1. The debris remained in the general area.
2. The structural integrity of the house(s) remained questionable.
Now, the first one may valid the most, but I haven't seen many pre-cleanup pics yet. The problem with using the first reason, however, is that this may be a strong function of tornado residence time over a location. For example, take a tornado with winds near 200mph, and keep it over one house for 30 1 minute, and I will bet that the debris is MUCH more scattered than a 250mph tornado that moves over a location for only 10 seconds. Part of the reason why the Jerrel pics showed parts of the damage path being completely devoid of debris likely has to do with the fact that the tornado moved quite slowly.
The second reason also is can be sketchy, since it seems legit if there are stronger structures that remain standing, but seems sketchy if all other structures (trees, etc) are gone. For the first, take La Plata. Some houses were initially rated F4 or higher because the foundation was wiped clean. However, some detailed work (see Tim Marshall's talk at
http://www.nssl.noaa.gov/nsww2003/talks/Ti...im_Marshall.htm ) showed that the houses literally "slid" off their foundations when winds could have been <150mph! However, for the second, one of the main drawbacks of the Fujita scale resurfaces. Say one tornado hits a weak house and the house is completely obliterated, while a second tornado hits a strong house and the house is completely obliterated. Can we say anything about the strength of the two tornadoes relative to each other? Was the second tornado necessarily stronger than the first? No. Both completely obliterated the houses they hit. We can know with more certainty that the second tornado (which hit the 'strong' house) was likely violent, but we can't necessarily conclude the first tornado (that hit the weak house) was weaker than the second, nor can we conclude that it wasn't weaker than the second. This deals with the same problem of an obviously strong or violent tornado staying in a field in western KS and not hitting anything. Everyone may know it was a strong or violent tornado, but *technically*, it may only be able to be classified as an F1.
I can imagine that there are some signficant difficulties when "weak" houses get completely destroyed, since we can usually only say then that the tornado was "at least a strong F3", or something to that tone. It is at this time that the damage assessment team must examine surrounding damage to see if they can rate it higher. How did trees fare? What about the roads? Was asphalt completely scoured of does a road reman? Indeed, in cases such as this, it's much easier to put a minimum rating on a tornado (e.g. - this tornado was at least a weak F4) than to determine it's max rating, since, as has been discussed a plethora of times, there may not be any recognizable damage to say with certainty that a tornado was an F5...
I don't want to rehash the oft-discussed drawbacks of the Fujita scale, since it has been discussed indepth a multitude of times before, and is likely of little utility in the absense of the power to do something about it, but thought I'd atleast give my thoughts...
