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Enhanced Fujita Scale

The Enhanced Fujita Scale (EF Scale) rates the strength of tornadoes in the United States based on the damage they cause. Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it became operational on February1, 2007. 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.

SCALE  WIND/MPH  FREQUENCY
EF0    65-85     53.5% Minor Damage.
Peels surface off some roofs; some damage to gutters and 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    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   10.7% Considerable Damage
Roofs torn off well-constructed homes; 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   3.4% Severe Damage
Entire stories of well-constructed homes destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off ground and thrown; structures with weak foundations blown away some distance.
EF4    166-200   0.7% Devastating Damage
Well-constructed homes and whole frame houses completely leveled; cars thrown and small missiles generated.
EF5    >200      <0.1% Extreme Damage
Strong frame homes leveled off foundations and swept away; automobile-sized missiles fly through air in excess of 100m (300 ft)' steel reinforced concrete structure badly damaged; high-rise buildings have significant structural deformation.

Source: http://en.wikipedia.org/wiki/Enhanced_Fujita_Scale#Parameters

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