Enhanced F Scale for Tornado Damage

NOAA ^ | Feb 2007 | NOAA

[xcamel]

Enhanced F Scale for Tornado Damage

An update to the the original F-scale by a team of meteorologists and wind engineers, to be implemented in the U.S. on 1 February 2007.

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FUJITA SCALE			DERIVED EF SCALE		OPERATIONAL EF SCALE
F Number	Fastest 1/4-mile (mph)	3 Second Gust (mph)	EF Number	3 Second Gust (mph)	EF Number	3 Second Gust (mph)
0	40-72	45-78	0	65-85	0	65-85
1	73-112	79-117	1	86-109	1	86-110
2	113-157	118-161	2	110-137	2	111-135
3	158-207	162-209	3	138-167	3	136-165
4	208-260	210-261	4	168-199	4	166-200
5	261-318	262-317	5	200-234	5	Over 200

*** IMPORTANT NOTE ABOUT ENHANCED F-SCALE WINDS: The Enhanced F-scale still is a set of wind estimates (not measurements) based on damage. Its uses three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to the 28 indicators listed below. These estimates vary with height and exposure. Important: The 3 second gust is not the same wind as in standard surface observations. Standard measurements are taken by weather stations in open exposures, using a directly measured, "one minute mile" speed.

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Enhanced F Scale Damage Indicators

NUMBER (Details Linked)	DAMAGE INDICATOR	ABBREVIATION
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	TS

A 95 page PDF file explaining the development and makeup of the Enhanced F-scale now is available, both here at SPC and from the Texas Tech server.

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Back to The Online Tornado FAQ

Enhanced F-scale Website

SPC Home Page

[xcamel]

This is to clear up why it seems the press is "under reporting" tornado wind strength, in light of the recent events.

I doubt Dr. Fujita would be very happy with this "new scale"

[aft_lizard]

Who knows, he said his old scale was not perfect and it needed improvements.

[mnehring]

It's not that the wind is blowing, it is what the wind is blowing...

[CindyDawg]

Clear as mud to me:’)

[Psycho_Bunny]

Why would he be unhappy with it? He agreed his scale was flawed.

[xcamel]

True. A plastic bottle cap at 200 mph can and will kill you... now imagine 80% of an entire town... airborne.... at 200 MPH

[xcamel]

His comment about “flawed” had to do with under reporting strength/damage ratios, and it was a huge political (politically correct) fight to get number approaching 300 mph even discussed openly. He knew higher was not only possible, but likely. The technology to accurately measure 10 second bursts (not 3 second like was agreed to) didn’t exist at the time. It does now, and he was dead on right... they (NOAA) are underreporting on purpose.

[aft_lizard]

From one of your links: http://www.spc.noaa.gov/efscale/ Over the years, the F-Scale has revealed the following weaknesses: It is subjective based solely on the damage caused by a tornado No recognition in difference in construction Difficult to apply with no damage indicators if the 3/4-mile wide tornado does not hit any structures, what F-scale should be assigned? Subject to bias Based on the worst damage (even if it is one building or house) Overestimates wind speeds greater than F3

[aft_lizard]

Well if it’s any consolation peak shear force winds were as high as 240 knots according to radar for the Greensburg Tornado.

[xcamel]

Known flaw with a damage only scale. Multipoint Doppler solves this with 3D wind speed readings. - Dr. F used to use the analogy of “If a tree falls in the woods and nobody hears it, was it loud?”

[aft_lizard]

OK then a reply would be to that is, “Which is worse if you are driving a SUV getting hit by a yugo doing 100mph or getting hit by a semi doing 75 mph?”

[aft_lizard]

Let me correct this:

OK then a reply would be to that is, “Which is worse if you are driving a SUV getting hit by a yugo and it is going 100mph or getting hit by a semi going 75 mph?”

[xcamel]

“Yes”
:-)

[skinkinthegrass]

...or a straw @ 400 mph....straight though a telephone pole.

[aft_lizard]

It’s not the wind alone that does that, it’s the pressure differences inside of the cyclone that can, for lack of a better word, soften the telephone pole.

I guess my point I am trying to make is that the size+speed is more important than just speed alone.

[xcamel]

it all comes down to mass in motion — basic physics.

[stevie_d_64]

Having worked in the structural engineering field for a few years, I can see the corrolation between the different levels of intensity of a tornadic event and the structures it “could” effect, depending on that force acting on the structure...

But...

To me its all destructive, and dependent upon a few other factors in how a structure “might” fail...And it all happens so fast it is just impossible to design effectively enough to counter all the variables you could possibly compile into the design...

You can do your best, and there are guidelines and industry standards...But you can only do so much...

I would say that its important to go as far as you can with what you have available, but always look for ways to encourage people to prepare for the worst, and create plans and shelter you can get to very quickly that anyone can take advantage of to protect lives...

Anyone who has looked at the devastation in that town, if you notice how many (below ground) shelters beside those destroyed homes in those pictures, showed the doors open, know that those shelters saved lives, and that is the best thing yet out of this whole ordeal...

[xcamel]

Right on the money.
Photo #20 from the KC arial site is a perfect example of a "safe room" built into the structure of the house. It mas mostly undamaged, and saved an entire family.

[M Kehoe]

I didn't see , "Common soda straw half way through palm tree," listed up there.

5.56mm

[stevie_d_64]

Those look like APB’s (Anthony Power Beams) coming across the top of those internal wall frames out from theat center room (shelter)...

I saw that pic yesterday, but it didn’t register till you mentioned it...

If they had more incentive to make “internal” armored rooms that would either be “no cost” or give a substantial insurance break to homes built in areas like this would really save a lot of lives if you ask me...

I’m having one built into our new home this time...No breaks for us, except peace of mind, and the skill to make use of it when the need arises...