Most tornado's have a speed of at least 110 mph (177 km/h). They are approximately 250 feet(80 m) across and can travel several miles/kilometres before dissipating.
A tornado is not always visible. A funnel cloud or Condensation cloud is it's most common feature. It is formed at intense low pressure causing high speeds(Bernoulli's Principle) and rapid rotation due to cyclostrophic balance, which causes water vapour in the air to become visible as a cloud. It is funnel shape.
Tornado's vary in size. Some are narrow, others are much larger. Small tornado's are weak. There may be a small swirl of dust. Average speed is 40 mph or 64 km/h. A 'stovepipe' is a cylindrical tornado. It can appear wedge like.
Tornado's rotate cyclonically(Anti Clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). This is because of the Coriolis affect. A tornado has a rumbling sound.
The colour is determined by it's environment. In a dry environment it is nearly all visible, if over water it can be blue or white. The type of soil may also contribute to the colour. The time of day will affect colour also.
The life cycle is broken up into different stages. Formation, Maturity, Demise.
Formation:
As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating wall cloud.As the funnel descends, the RFD(Rear flank downdraft) also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud becomes a tornado within minutes of the RFD reaching the ground.
Maturity:
When the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the "mature stage". This can last minutes to hours. This is the stage that causes most damage. The RFD now an area of cool surface winds, begins to wrap around the tornado, cutting off the inflow of warm air which feeds the tornado.
Demise:
As the RFD completely wraps around and chokes off the tornado's air supply, the vortex begins to weaken, and become thin and rope-like. This is the "dissipating stage"; often lasting no more than a few minutes, after which the tornado fizzles. The storm is contracting into a rope-like tube and, like the ice skater who pulls her arms in to spin faster, winds can increase at this point. As the tornado enters the dissipating stage, its associated mesocyclone often weakens as well, as the rear flank downdraft cuts off the inflow powering it.
The Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. The Enhanced Fujita (EF) Scale was an upgrade to the older Fujita scale, by expert elicitation, using engineered wind estimates and better damage descriptions. The EF Scale was designed so that a tornado rated on the Fujita scale would receive the same numerical rating. An EF0 tornado will probably damage trees but not substantial structures, whereas an EF5 tornado can rip buildings off their foundations leaving them bare and even deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.
