Light damage. Some damage to chimneys; break
branches off trees; push over shallow-rooted trees; damage sign
boards.
(F1) Moderate tornado (73-112
mph)
Moderate damage. The lower limit is the beginning
of hurricane wind speed;peel surface off roofs; mobile homes pushed
off foundations or overturned;moving autos pushed off the
roads.
(F2) Significant tornado
(113-157 mph)
Considerable damage. Roofs torn off frame houses;
mobile homes demolished;boxcars pushed over; large trees snapped or
uprooted; light-object missiles generated.
(F3) Severe tornado
(158-206 mph)
Severe damage. Roofs and some walls torn off
well-constructed houses; trains overturned; most trees in forest
uprooted; heavy cars lifted off the ground and thrown.
(F4) Devastating tornado
(207-260)
Devastating damage. Well-constructed houses
leveled; structures with weak foundations blown off some distance;
cars thrown and large missiles generated.
(F5) Incredible tornado
(261-318 mph)
Incredible damage. Strong frame houses lifted off
foundations and carried considerable distance to disintegrate;
automobile sized missiles fly through the air in excess of 100 meters
(109 yds); trees debarked; incredible phenomena will occur.