How would you rate a tornado based on ground scouring alone

[STurner]

I was just wondering how they rate a tornado if their is massive ground scouring and that is all that occured. I dont think it would be rated high on the EF-scale because it is not the best indicator. It just seems that a lot of strong/violent tornadoes were associated with massive scouring of the ground and in addition to whatever else was damaged.

 

[rdale]

You wouldn't rate it very high unless it did some damage.

 

[Angie Norris]

No damage to structures or trees? I'd think it would default out to an EF-0.

 

[rdale]

There are ways of ranking based on corn field scattering - check Dr F's work on the Plainfield IL tornado.

 

[STurner]

There are ways of ranking based on corn field scattering - check Dr F's work on the Plainfield IL tornado.

I thought Fujita rated this tornado an F5 based upon the most amazing vegetation scouring he had ever seen. There was also a lot of major damage that also occured in the Plainfield tornado. Even if no damage to structures occured, wouldn't amazing ground scouring just like the Plainfield tornado indicate it was a pretty storng tornado.

 

[Jeff Richardson]

I believe Dr. Fujita ranked the Plainfield, IL tornado based on a combination of the damage to the corn field vegetation and the distances/trajectories traveled by several vehicles that were blown from an adjacent highway. The supplement to Significant Tornadoes (if you can still find one) has a great deal of information on Fujita's damage survey of this particular storm. By today's standards with the EF scale, I'm sure the same tornado would receive a lower rating. But, since the old and new Fujita scales are a human risk assessment tool, I would assume that even a violent tornado would not be given a high EF scale rating based on crop/vegetation damage alone, regardless how spectacular it might be. Tim Marshall and others who worked on the EF Scale would be able to give a more detailed answer.

 

[Rob Wadsworth]

Here's a 'curveball', Some 'naders have taken topsoil - up to a couple of feet deep. Not comon - bu it happens. As well as taking out asphalt - too. Surely, the f-scale hasn't taken this in to account. Could be wrong, but I haen't seen it anywhere yet. Of course, the f-scale is all about building damage assesment. No buildings or structures - no assessment.
Hey, there goes a cow!

Seriously though, if a 'nader is taking out soil or a roadway - it should get some consideration by those who make/change the scale assessments. Too often 'naders don't really knock something over. It's too bad that chasers or the NWS don't have a radar gun that can calibrate wind speed at the base of the tube or its middle portion - so that data can be logged in. Otherwise, it becomes a bit difficult to quantify any one 'nader potential.
Just a thought or three.

 

[Scott Weberpal]

Seriously though, if a 'nader is taking out soil or a roadway - it should get some consideration by those who make/change the scale assessments.

Relatively weak tornadoes can scour pavement, especially if it's blacktop. Once the wind gets under a layer of concrete of blacktop, it will have no problem lifting out large chunks. I was at a talk about this a few years back (I believe Tim M. was the presenter), and it was noted that even an EF1 tornado could scour pavement especially if the pavement is already loose or layered without being sealed.

 

[Chad Cowan]

Of course, the f-scale is all about building damage assesment. No buildings or structures - no assessment.

Not true. Both the F and EF scales use all available data to ascribe a rating. This includes "radar data, photogrammetry, cycloidal marks (ground swirl patterns)" and vegetation (Damage Indicators 27 & 28 on the EF scale).

It's too bad that chasers or the NWS don't have a radar gun that can calibrate wind speed at the base of the tube or its middle portion -

We do. They're called mobile radars

 

[Rob Wadsworth]

Yeah, I got one - as in a laptop and GR3. Iwas thinking along the lines of real-time. I was thinking out loud for a handheld unit like the police use to check cars for speeding.
It was meant to be semi-serious and humerous.
Structure damage is the way that EF can get some real concept of actual wind speed vs damage. Rating an old building wind damage w/o uniform building codes isn't as exacting as Universal building code and wind damage. There might have been something there about road damage, but I don't recall. Good to know though - thanks...

 

[Darren Addy]

It is hard for people to wrap their minds around this, but the scale is a damage rating - not a tornado rating. I think a good analogy would be the medical rating for burns. You have 1st degree, 2nd degree, and 3rd degree burns (and you have them over a certain percentage of your body). The damage of the burn doesn't say a lot about the severity of the actual heat that caused the burn. The damage is a combination of the heat and the proximity and the time in contact with the skin.

Similarly the EF/F scale is rating the damage, which tells us something about the originating tornado, but not everything. As humans we want to classify everything and so we think we are classifying tornadoes, but we are really only classifying the thing we can wrap our arms around: the resulting damage.