Tornadoes are funnel shaped clouds that are associated with thunderstorms. Tornadoes have wind velocities higher than hurricanes (up to 500 km/hr [318 miles per hour]), but affect a much smaller area than hurricanes. Tornadoes are mostly found in inland areas with high convection rates.
Tornado Development - A tornado develops within a severe thunderstorm when there is an excessive amount of vertical wind shear. Vertical wind shear is when upper level winds are blowing at a high velocity relative to lower level winds. Prior to the development of the thunderstorm strong high level winds blowing to the west initiates a spinning flow near the Earth's surface. This spinning flow takes the form of an invisible horizontally oriented cylinder. As the thunderstorm develops, strong updrafts of warm air lifts this rotating air into a more vertical position within the thundercloud, causing part of the thundercloud to rotate around the a vortex in a counterclockwise direction. Tornadoes form within this rotating air, usually at the rear flank of the thunderstorm, and extend down from the thundercloud occasionally reaching the surface. They travel at velocities between stationary and 110 km/hr, with cyclonic wind speeds up to 500 km/hr as noted above. The diameters of tornadoes range from a few tens of meters up to 1.5 km. They do not often remain in contact with the ground for long periods of time, but can skip across the surface as the thunderstorm moves along.
|After National Weather Service (1992)|