From AMS Glossary
(Also known as the F-scale.) Relates tornado intensity indirectly to structural and/or vegetative damage.
The estimated wind speed is calculated using the following formula: V = 6.30 (F+2)1.5 m s-1. A six-point scale has been developed that corresponds to the following wind-speed estimates:
- F0 (light damage): 18–32 m s-1
- F1 (moderate damage): 33–49 m s-1
- F2 (considerable damage): 50–69 m s-1
- F3 (severe damage): 70–92 m s-1
- F4 (devastating damage): 93–116 m s-1
- F5 (incredible damage):117–142 m s-1.
Although extremely dependent on the design of a structure and the tree type, the following visual characteristics of the damage have been assigned to the F-scale.
- F0 - Some damage to chimneys; branches broken; shallow-rooted trees knocked over.
- F1 - Surface of roofs peeled off; mobile homes pushed off foundations or overturned; moving autos pushed off road.
- F2 - Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted.
- F3 - Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.
- F4 - Well-constructed houses leveled; structures with weak foundations blown off; large missiles generated.
- F5 - Strong frame houses lifted off foundations and carried considerable distances; automobile- sized missiles flying through the air for distances in excess of 100 m; trees debarked.
Fujita, T. 1981. Tornadoes and downbursts in the context of generalized planetary scales. J. Atmos. Sci.. 38. 1511–1534.