wind speed :300 ~350mph -500 mph
lifetime :10 mins - 2 hrs
track length: few miles - 100 miles ( 0.5 % )
Shape : long, thin rope, an elephant's trunk, fat inverted bell
Colour :as white as the whitest cloud, as black as soot ( the black colour coming from the dirt they pick up )
Centre of the funnel:circular opening : ~ 50 - 100 ft in diameter, extending striaght upward for a distance of at least 1/2 miles. the walls are of rotating clouds, with constant flashes of lightning which zig-zag from side to side.
around the lower rim of great vertex:small tornadoes are constantly forming and breaking away. Small twisters have same or different rotating direction as great whirl.
Destructiveness: When a tornado attacks a house, the structure behaves like an aircraft wing. The faster the air, the lower the pressure; the slower the air, the higher the pressure.
The tornado wind rushes at the front wall, and this barrier forces the wind over the roof and side walls of the house. The air inside is now at higher pressure and exerts a thrust on the roof, on the side walls, and to a lesser extent on the leeward wall.
160mph wind will produce a lifting force of over 30 tons on a typical house. 300 mph, about 2 times more, will produce a lifting force of 100 tons.
The usual effect :roof lifts up, wall weaken, front wall blows in, side walls blow out, rear wall falls down and out and then roof falls in. But neither the roof nor the walls are necessarily swept away.
Houses are much harder to lift when lying flat on the ground than they are when upright.
Waterspouts are tornadoes' ocean equivalents.
Cloud shapes known as a signature of potential tornadoes:
i)Bright V-shaped cloud wedge with overshooting towers of convection
ii)Pendulous mammatus cloud
iii)Rotatory circulation in wind-tattered cloud bases
When a tornado does appear, it usually comes out of the storm's rear side, near where a stream of cool air from a vertical downdrafr spins into the warm, low level horizontal inflow. Horizontal winds are apparently capable of assisting the formation of the violent vertical updraft characteristic of a tornado.
In U.S., about 1/3 tornadoes ravage just 3 states : Texas, Oklahoma, Kansas. Warm, moist air flowing up from the Gulf of Mexico meets cool, dry air from Canada channelled east by the Rockies, would precipitate the formation of the twisters.