Tornadoes
Tornadoes in Southwest Idaho and Southeast Oregon are relatively rare and
those that do form are usually in the F0 category. However, strong tornadoes are
possible in this area, they are just very rare. Southwest Idaho and Southeast
Oregon average about 3 tornadoes per year. Some years none form, other years
10 or more may form. Tornadoes in this area are most frequent in early and mid
summer, but tornadoes can form at any time of year.
Tornado strength is measured by the Fujita Scale. The Fujita scale is an
attempt to relate tornado damage to the maximum wind in the tornado. The weakest
tornadoes are rated F0 and can only produce very minor damage. The strongest
tornadoes believed to exist are F5 and produce incredible damage with winds in
excess of 300 mph. It is believed that tornadoes are not capable of producing
winds in excess of 380 mph, thus F6 are the strongest tornadoes possible.
However, estimating damage above 318 mph and directly measuring wind speed
in a tornado are nearly impossible, thus F5 are the strongest confirmed tornadoes.
| F0 |
less than 73 mph |
Minor Damage |
| F1 |
73 to 112 mph |
Moderate Damage - Peels surface off roofs; windows broken; trailor houses pushed or overturned; trees on soft ground uprooted; some trees snapped; moving autos pushed off the road. |
| F2 |
113 to 157 mph |
Considerable Damage - Roof torn off frame houses leaving strong upright walls standing; weak structures or outbuildings demolished; trailor houses demolished; railroad boxcars pushed over; large trees snapped or uprooted; light-object missiles generated; cars blown off highway; block structures and walls badly damaged. |
| F3 |
158 to 206 mph |
Severe Damage - Roofs and some walls torn off well-constructed frame houses; some rural buildings completely demolished or flattened; trains overturned; steel framed hanger-warehouse type structures torn; cars lifted off the ground and may roll some distance; most trees in forest uprooted, snapped or leveled; block structure often leveled. |
| F4 |
207 to 260 mph |
Devastating Damage - Well-constructed frame house leveled, leaving piles of debris; structure with weak foundation lifted, torn, and blown some distance; trees debarked by small flying debris; sandy soil eroded and gravels fly high in the wind; cars thrown some distance or rolled considerable distance finally to disintegrate; large missiles generated. |
| F5 |
261 to 318 mph |
Incredible Damage - Strong fram houses lifted clear off foundation and carried considerable distance to disintegrate; steel-reinforced concrete structures badly damaged; automobiles-sized missiles fly through the distance of 100 yards or more; trees debarked completely; incredible phenomena can occur. |
| F6 |
319 to 379 mph |
Inconceivable Damage - Large objects such as storage tanks and automobiles will fly through a long distnace; home foundations ripped from ground. Assessment of tornadoes in these categories is feasible only through detailed survey involving engineering and areodynamical calculations as well as meteorological models of tornadoes. |
| F7 - F12 |
380 mph to the Speed of Sound |
Not expected to occurr! |
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