Originally posted by Alex Lamers
How do you account for the REALLY strong EF5's then like the Moore tornado would have been? 318 mph?
IDK. What is the basis for the change anyways. Why can't they just make damage indicators for the old fujita scale?
Someone tell me the advantage of the switch, not just information about it.
...Alex Lamers...
How do we account for REALLY strong Cat 5s? There is no upper bound, so a 300mph MEASURED wind speed is still in the EF5 range, just as a 215mph sustained speed in a hurricane is still a Cat 5.
The old F-scale HAD wind speeds attached to it that were unrealistically high. It's been tested that 220mph winds aren't required to obliterate a house, like the original F-scale implied (F4 or greater). It doesn't make sense to me to enhance the scale without making necessary changes to the wind speeds associated with each category.
As stated above, even if a tornado is MEASURED (by a miracle anemometer) to have 500mph winds, it'll still be given an EF-5 rating if I understand things correctly. In addition, the obliteration of a wellbuilt structure will still earn a 'violent' rating. This just gives us an advantage of having more indicators to deal with those situations in which there aren't well-built homes damaged (which happens a lot). Heck, even having tree damage as an indicator is nice, and I'd expect that it'll help standardize rating assessments when those 'well-built' homes aren't affected or aren't affected directly.
I'm not sure we'll see a large rise in level-4 or level-5 rated tornadoes (compared to historical F4 and F5 tornadoes) when the EF scale comes out since it's still based on damage! I DO think we may see a couple more EF-4s than F4s we've had recently since there are more damage indicators to help with an assessment. Even at that, violent tornadoes from at least the past few years were rated by a panel of damage experts that were no doubt well-qualified to make such assessments. So, a tornado that rips the roof off a house won't be rated EF5, just as it wouldn't be rated an F5 now. Just my 2 cents. This just goes to show how many previous tornadoes had winds that were likely considerably weaker than previously thought. I don't think it says much about whether previous tornadoes were over-rated, since the F-scale is a damage scale, so F5 damage is F5 damage. Now, however, we just see that 300mph probably aren't necessary to obliterate structures.
I also like how the wind bounds don't imply a precision that we don't have. By saying that the an F3 tornado has winds of 158-207mph implies a precision that is unfounded. The EF-scale rounds the upper-bounds to x0 or x5 (e.g. EF3 foes from 136-165mph).
Damage indicators:
1 Small barns, farm outbuildings SBO
2 One- or two-family residences FR12
3 Single-wide mobile home (MHSW) MHSW
4 Double-wide mobile home MHDW
5 Apt, condo, townhouse (3 stories or less) ACT
6 Motel M
7 Masonry apt. or motel MAM
8 Small retail bldg. (fast food) SRB
9 Small professional (doctor office, branch bank) SPB
10 Strip mall SM
11 Large shopping mall LSM
12 Large, isolated ("big box") retail bldg. LIRB
13 Automobile showroom ASR
14 Automotive service building ASB
15 School - 1-story elementary (interior or exterior halls) ES
16 School - jr. or sr. high school JHSH
17 Low-rise (1-4 story) bldg. LRB
18 Mid-rise (5-20 story) bldg. MRB
19 High-rise (over 20 stories) HRB
20 Institutional bldg. (hospital, govt. or university) IB
21 Metal building system MBS
22 Service station canopy SSC
23 Warehouse (tilt-up walls or heavy timber) WHB
24 Transmission line tower TLT
25 Free-standing tower FST
26 Free standing pole (light, flag, luminary) FSP
27 Tree - hardwood TH
28 Tree - softwood
Since it wasn't directly linked to previously, you can read the full report at
http://www.spc.noaa.gov/faq/tornado/ef-ttu.pdf , which explains how the EF scale was derived, how the EF scale correlates to the F scale, etc.
Originally posted by EF-Scale Report+ page 15 of the pdf--><div class='quotetop'>QUOTE(EF-Scale Report]
Members of the Forum were very specific in their opinion that a single building, structure, or other DI should not be used to rate a tornado event. Several DIs should be considered in assigning an EF-Scale rating to a tornado event.[/b]
That would imply that a single damage indicator that would imply an EF4, for example, does not necessary guarantee that an EF4 rating would be accurate.
<!--QuoteBegin-EF-scale Report@ pg. 17-18 of the pdf
The estimated wind speed then determines the EF-Scale category appropriate for the observed damage. The categories range from EF0 to EF5. The wind speed ranges in each category are related to Fujita Scale ranges by a correlation function (Equation 1). This correlation between Fujita-Scale and EF-Scale wind speeds provides a link between the two scales and thus makes it possible to express a Fujita-Scale rating in terms of an EF-Scale rating. The only difference is the wind speed ranges in each scale. Thus, the historical tornado database is preserved and can be easily converted to the criteria of the EF Scale.
The problem of no DIs in open country remains. Research is currently underway to identify additional damage indicators and to obtain estimates of the wind speeds to cause defined damage. Of particular interest are damage to various crops, farm equipment, silos, grain storage facilities, and irrigation equipment. These indicators can be incorporated as DIs in the EF Scale as reliable data become available. The technology of portable Doppler radar should also be a part of the EF Scale process, either as a direct measurement, when available, or as a means of validating the wind speeds estimated by the experts.[/quote]
{Emphasis added by me}
The last sentence is interesting, in that it implies (to me at least) the mobile Doppler radar measurements CAN now be ground for assigning a rating to a tornado. Of course, there are plenty of unknowns still, such as the problem of estimating near-surface (10m) winds from velocity data obtained well above that level. I would take this to mean that if a tornado sits in a field and does very little damage, a DOW ob (surface-extrapolated, however that will happen) of 180mph may be sufficient in assigning an EF4 rating. On the other hand, this now makes wind speeds a more integral part of the EF-scale (e.g it's no longer a PURELY damage-based scale!).
Of course, my understanding of this may be incorrect, so it'd be nice to hear from someone more involved in the EF-scale.
