Weather Facts

Tornado's are natures most violent storms on earth with estimated wind speeds in excess of 300 miles per hour. A Tornado is a rotating column of air that connects all the way to the ground from the base of a thunderstorm. The rotating motion of a thunderstorm is mostly counterclockwise (cyclonic rotation).

Thunderstorms develop when warm moist air and cool and dry air mix. (warm, moist, cool and dry are relative terms in weather. This means when a warm or cold front is moving in, it can only be a few degrees warmer or colder, the larger the difference is, the better chance of severe weather).

The figure below is the Fujita scale, it measures the intensity of tornados by the amount of damage it causes (not by how large it is).

Category

Wind Speed

Effects

F0

40-72 mph

Light damage: Some damage to chimneys; branches break from trees; shallow rooted trees pushed over; sign boards damaged

F1

73-112 mph

Moderate damage: Roof surfaces peeled off; mobile homes pushed from foundations or overturned; cars pushed off roads

F2

113-157 mph

Considerable damage: Roofs torn off frame houses; mobile homes demolished; large trees snapped or uprooted

F3

158-206 mph

Severe damage: Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted

F4

207-260 mph

Devastating damage: Well-constructed houses leveled; structures with weak foundations blown off some distance

F5

261-318 mph

Incredible damage: Strong frame houses lifted off foundations and carried considerable distance to disintegrate

F0 and Fl tornadoes comprise 70% of all tornadoes that occur in the U.S. They usually touch down briefly and cause minor damage. However, forecasting these tornadoes is less reliable than for stronger tornadoes, so less than 50% occur during tornado watches.

F2 and F3 tornadoes comprise about 28% of the tornadoes in the U.S. They can cause significant damage, injuries, and deaths.

F4 and F5 tornadoes comprise about 2 percent of the tornadoes in the U.S. and cause 70% of the death and destruction. Fortunately, the NWS has identified precursor conditions for the more damaging tornadoes. Over 95% of these tornadoes, therefore, occur during tornado watches.

Data from the National Weather Service

There four types of thunderstorms

1. Single-cell thunderstorm

2. Multi-cell Thunderstorm

3. Squall Line

4. Super Cell thunderstorm

Category	Wind Speed	Effects
F0	40-72 mph	Light damage: Some damage to chimneys; branches break from trees; shallow rooted trees pushed over; sign boards damaged
F1	73-112 mph	Moderate damage: Roof surfaces peeled off; mobile homes pushed from foundations or overturned; cars pushed off roads
F2	113-157 mph	Considerable damage: Roofs torn off frame houses; mobile homes demolished; large trees snapped or uprooted
F3	158-206 mph	Severe damage: Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted
F4	207-260 mph	Devastating damage: Well-constructed houses leveled; structures with weak foundations blown off some distance
F5	261-318 mph	Incredible damage: Strong frame houses lifted off foundations and carried considerable distance to disintegrate
F0 and Fl tornadoes comprise 70% of all tornadoes that occur in the U.S. They usually touch down briefly and cause minor damage. However, forecasting these tornadoes is less reliable than for stronger tornadoes, so less than 50% occur during tornado watches. F2 and F3 tornadoes comprise about 28% of the tornadoes in the U.S. They can cause significant damage, injuries, and deaths. F4 and F5 tornadoes comprise about 2 percent of the tornadoes in the U.S. and cause 70% of the death and destruction. Fortunately, the NWS has identified precursor conditions for the more damaging tornadoes. Over 95% of these tornadoes, therefore, occur during tornado watches. Data from the National Weather Service