Tornadoes are impressive, but potentially dangerous, storms. Click image for larger view.
Forecasters and researchers currently use a wind damage scale created in 1972 by T. Theodore Fujita to classify tornadoes and sometimes the damage done by other wind storms. The F (for Fujita) - scale uses numbers from 0 through 5. The ratings are based on the amount and type of wind damage.
Fujita Tornado Damage Scale
Category F0: Light Damage (<73 mph); some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.
Category F1: Moderate Damage (73-112 mph); peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off road.
Category F2: Considerable Damage (113-157 mph); roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
Category F3: Severe Damage (158-206 mph); roofs and some walls torn off well-constructed houses, trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.
Category F4: Devastating Damage (207-260 mph); well-constructed houses leveled; structure with weak foundations blown off some distance; cars thrown and large missiles generated.
Category F5: Incredible Damage (261-318 mph); strong frame houses lifted off foundations and swept away; automobile sized missiles fly through the air in excess of 100 meters (109 yards); trees debarked; incredible phenomena will occur.
IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These wind speed numbers are estimates and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place - even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.