This week is tornado awareness week and only in America! It is a campaign to get people more organised and prepared for when the big one hits.
It is also about informing the public about the different types and strengths of a twister.

Tornadoes are reported all over the world each year — in places like Australia, Europe, Africa and Asia — and can occur wherever thunderstorms form. However, the most active area on earth for severe weather lies in the United States, where an estimated 1,000 tornadoes are reported every year.

After a tornado touches down, it typically tracks along the ground for a few kilometres or less, though some tornadoes can remain in contact with the ground for more than 80 kilometres and span more than a 2 km in width.

The winds inside most tornadoes blow at 160 kph or less, but in the most violent tornadoes, wind speeds can exceed 330 kph. (Thankfully, these monsters are also rare.)

Tornadoes can appear in the familiar funnel shape seen in countless television clips, or in a slender, rope-like form. While some tornadoes are marked by a dark, smoky, churning appearance, others may be virtually invisible, detectable only by swirling dust or debris.

Weak tornadoes

Comprise 69% of all tornadoes
Cause less than 5% of all tornado deaths
Have a lifetime of between 1 – 10 minutes
Wind speeds measured at less than 175 kph

Strong tornadoes

Comprise 29% of all tornadoes
Cause nearly 30% of all tornado deaths
May last 20 minutes or longer
Wind speeds measured at between 175-270 kph

Violent tornadoes

Comprise 2% of all tornadoes
Cause 70% of all tornado deaths
Have a lifetime of 1 hour or longer

TheWeatherChannel