(F0) Gale tornado (40-72 mph): 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 off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off 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; heavy cars lifted off ground and thrown.
(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 ground and thrown.
(F4) Devastating tornado (207-260 mph): Devastating damage. Well-constructed houses leveled; structure with weak foundation 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 through the air in excess of 100 yards; trees debarked; incredible phenomena will occur.