The
Enhanced Fujita Scale, or EF
Scale, is the scale for rating the strength of tornadoes in the United States
estimated via the damage they cause.
Implemented in place of the
Fujita
scale introduced in 1971 by
Ted
Fujita, it began operational use on February 1, 2007. The scale
has the same basic design as the original Fujita scale, six
categories from zero to five representing increasing degrees of
damage. It was revised to reflect better examinations of tornado
damage surveys, so as to align wind speeds more closely with
associated storm damage. Better standardizing and elucidating what
was previously subjective and ambiguous, it also adds more types of
structures as well as vegetation, expands degrees of damage, and
better accounts for variables such as differences in construction
quality.
The new
scale was publicly unveiled by the National Weather Service at a
conference of the American Meteorological
Society in Atlanta
on February
2, 2006. It was developed from 2000 to 2004 by the
Fujita Scale Enhancement Project of the Wind Science and Engineering Research
Center
at Texas Tech University
, which brought together dozens of expert
meteorologists and civil engineers in addition to its own
resources.
As with the Fujita scale, the Enhanced Fujita Scale remains a
damage scale and only a proxy for actual wind speeds. While the
wind speeds associated with the damage listed have not undergone
empirical analysis (e.g. detailed physical or any numerical
modelling) owing to excessive cost, the wind speeds were attained
through a process of
expert
elicitation based on various engineering studies since the
1970s as well as from field experience of meteorologists and
engineers. In addition to damage to structures and vegetation,
radar data,
photogrammetry, and
cycloidal marks (ground swirl patterns)
may be utilized when available.
The scale was used for the first time a year after its public
announcement when parts of central Florida were struck by
multiple tornadoes, the
strongest of which were rated at EF3 on the new scale.
The first time the EF5
assessment was used was the Greensburg, Kansas tornado
that occurred on May 4, 2007.
Parameters
The six categories for the EF Scale are listed below, in order of
increasing intensity. Although the wind speeds and photographic
damage examples are updated, the damage descriptions given are
those from the
Fujita scale, which are
more or less still accurate. However, for the actual EF scale in
practice, one must look up the damage indicator (the type of
structure which has been damaged) and consult the degrees of damage
associated for that particular indicator.
| Scale |
Wind speed |
Relative frequency |
Potential damage |
| mph |
km/h |
| EF0 |
65–85 |
105–137 |
53.5% |
Light damage.
Peels surface off some roofs; some damage to gutters or siding; branches broken off trees;
shallow-rooted trees pushed over.
Confirmed tornadoes with no reported damage (i.e. those that remain
in open fields) are always rated EF0. |
|
| EF1 |
86–110 |
138–178 |
31.6% |
Moderate damage.
Roofs severely stripped; mobile homes overturned or badly damaged;
loss of exterior doors; windows and other glass broken. |
|
| EF2 |
111–135 |
179–218 |
10.7% |
Considerable damage.
Roofs torn off well-constructed houses; foundations of frame homes
shifted; mobile homes completely destroyed; large trees snapped or
uprooted; light-object missiles generated; cars lifted off
ground. |
|
| EF3 |
136–165 |
219–266 |
3.4% |
Severe damage.
Entire stories of well-constructed houses destroyed; severe damage
to large buildings such as shopping malls; trains overturned; trees
debarked; heavy cars lifted off the ground and thrown; structures
with weak foundations blown away some distance. |
|
| EF4 |
166–200 |
267–322 |
0.7% |
Devastating damage.
Well-constructed houses and whole frame houses completely leveled;
cars thrown and small missiles generated. |
|
| EF5 |
>200 |
>322 |
<0.1%></0.1%> |
Explosive damage.
Strong frame houses leveled off foundations and swept away;
automobile-sized missiles fly through the air in excess of ; steel
reinforced concrete structure badly damaged; high-rise buildings
have significant structural deformation. |
|
Damage Indicators and Degrees of Damage
The EF Scale currently has 28 Damage Indicators (DI), or types of
structures and vegetation, with a varying number of Degrees of
Damage (DOD) for each.
| DI No. |
Damage Indicator (DI) |
Degrees of Damage (DOD) |
| 1 |
Small Barns or Farm Outbuildings (SBO) |
|
| 2 |
One- or Two-Family Residences (FR12) |
|
| 3 |
Manufactured Home – Single Wide (MHSW) |
|
| 4 |
Manufactured Home – Double Wide (MHDW) |
|
| 5 |
Apartments, Condos, Townhouses [3 stories or less] (ACT) |
|
| 6 |
Motel (M) |
|
| 7 |
Masonry Apartment or Motel Building (MAM) |
|
| 8 |
Small Retail Building [Fast Food Restaurants] (SRB) |
|
| 9 |
Small Professional Building [Doctor’s Office, Branch Banks]
(SPB) |
|
| 10 |
Strip Mall (SM) |
|
| 11 |
Large Shopping Mall (LSM) |
|
| 12 |
Large, Isolated Retail Building [K-Mart, Wal-Mart] (LIRB) |
|
| 13 |
Automobile Showroom (ASR) |
|
| 14 |
Automobile Service Building (ASB) |
|
| 15 |
Elementary School [Single Story; Interior or Exterior Hallways]
(ES) |
|
| 16 |
Junior or Senior High School (JHSH) |
|
| 17 |
Low-Rise Building [1–4 Stories] (LRB) |
|
| 18 |
Mid-Rise Building [5–20 Stories] (MRB) |
|
| 19 |
High-Rise Building [More than 20 Stories] (HRB) |
|
| 20 |
Institutional Building [Hospital, Government or University
Building] (IB) |
|
| 21 |
Metal Building System (MBS) |
|
| 22 |
Service Station Canopy (SSC) |
|
| 23 |
Warehouse Building [Tilt-up Walls or Heavy-Timber Construction]
(WHB) |
|
| 24 |
Electrical Transmission Lines (ETL) |
|
| 25 |
Free-Standing Towers (FST) |
|
| 26 |
Free-Standing Light Poles, Luminary Poles, Flag Poles
(FSP) |
|
| 27 |
Trees: Hardwood (TH) |
|
| 28 |
Trees: Softwood (TS) |
|
Differences from the Fujita scale
The new scale takes into account quality of construction and
standardizes different kinds of structures. The wind speeds on the
original scale were deemed by meteorologists and engineers as being
too high and engineering studies indicated that slower winds than
initially estimated cause the respective degrees of damage. The new
scale lists an EF5 as a tornado with winds at or above 200 mph
(324 km/h), found to be sufficient to cause the damage
previously ascribed to the F5 range of wind speeds. None of the
tornadoes recorded on or before January 31, 2007 will be
re-categorized.
Essentially, there is no functional difference in how tornadoes are
rated. The old ratings and new ratings are smoothly connected with
a linear formula. The only differences are adjusted wind speeds,
measurements of which weren't used in previous ratings, and refined
damage descriptions; to standardize ratings and to make it easier
to rate tornadoes which strike few structures. Twenty-eight Damage
Indicators (DI), with descriptions such as "
Double-wide mobile home" or "
Strip mall", are used along with Degrees of
Damage (DOD) to determine wind estimates. Different structures,
depending on their building materials and ability to survive high
winds, will have their own DIs and DODs. Damage descriptors and
wind speeds will also be readily updated as new information is
learned.
Since the new system will still use actual tornado damage and
similar degrees of damage for each category to estimate the storm's
wind speed, the National Weather Service states that the new scale
will likely not lead to an increase in a number of tornadoes
classified as EF5. Additionally, the upper bound of the wind speed
range for EF5 is open — in other words, there is no maximum wind
speed designated.
See also
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