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|1802 Hill Avenue
Spirit Lake, IA 51360
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Tornadoes – defined as a violently rotating column of air extending from a thunderstorm to the ground – are often formed when warm and cold air masses clash. They are capable of tremendous destruction, creating damage paths in excess of one mile wide and 50 miles long. Tornados speed can vary from nearly stationary to up to 70 mph; however, the wind speed from these formations can exceed 250 mph. Tornadoes are classified using the Enhanced Fujita Scale (Table 1). Most tornadoes (~88%) are considered weak (EF0 or EF1) and about 95% of all U.S. tornadoes are below EF3 intensity.
In the United States, on average, 1000 tornadoes are reported nationwide each year, resulting in 70 deaths and over 1,500 injuries. They occur most frequently east of the Rocky Mountains during the spring and summer months. The graphic on this page shows the distribution of tornado watches issued in the United States in 2010.
Tornado Alley is a nickname given to an area in the southern plains of the central U.S. that consistently experiences a high frequency of tornadoes each year.
Tornadoes can cause rapid destruction of homes and property, as well as injury and death to humans and animals. The following factsheets will help you prepare your family, home and farm, animals and business in efforts to minimize the impact from tornadoes and help to speed the recovery process.
Table 1. Enhanced Fujita Tornado Intensity Scale (F-Scale)
|Category||Description & Potential Damage|
|EF0||Gale tornado (40-72 mph); light damage.
Some damage to chimneys; break branches off trees; push over shallow-rooted trees; damage to sign boards.
|EF1||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.
|EF2||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.
|EF3||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.
|EF4||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.
|EF5||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 yards; trees debarked; incredible phenomena will occur.