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"(A tornado is "a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud.")" A vortex can only be classified as a tornado if it is connected from the ground to the cloud base. "Wind speeds in tornadoes range from values below that of hurricane speeds to more than 300 miles per hour!" "The maximum winds in tornadoes are often confined to extremely small areas, and vary tremendously over very short distances, even within the funnel itself". With this said, the stories you hear about one house being completely destroyed and it's neighbor, maybe a football feild away, looking untouched, are true.

"In 1971, Dr. T. Theodore Fujita of the University of Chicago devised a six-category scale to classify U.S. tornadoes into six intensity categories, named F0-F5. These categories are based upon the estimated maximum winds occurring within the funnel. The Fujita Tornado Scale, more commonly called the "F Scale", has subsequently become the accepted and recognized scale for estimating wind speeds within tornadoes based upon the damage done to buildings and structures.

TABLE FROM http://csgnetwork.com/tornadotable.html

Wind Speed MPH	Air Temperature (Degrees Fahrenheit)
Maximum Wind Speeds	Saffir-Simpson Scale*	Typical Effects
F0 Category Tornado
40-72 mph (35-62 kt)	NA	Gale Tornado. Light Damage: Some damage to chimneys; breaks twigs and branches off trees; pushes over shallow-rooted trees; damages signboards; some windows broken; hurricane wind speed begins at 73 mph.
F1 Category Tornado
73-112 mph (63-97 kt)	Cat 1/2/3	Moderate Tornado. Moderate damage: Peels surfaces off roofs; mobile homes pushed off foundations or overturned; outbuildings demolished; moving autos pushed off the roads; trees snapped or broken.
F2 Category Tornado
113-157 mph (98-136 kt)	Cat 3/4/5	Significant Tornado. Considerable damage: Roofs torn off frame houses; mobile homes demolished; frame houses with weak foundations lifted and moved; boxcars pushed over; large trees snapped or uprooted; light-object missiles generated.
F3 Category Tornado
158-206 mph (137-179 kt)	Cat 5	Severe Tornado. Severe damage: Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forests uprooted; heavy cars lifted off the ground and thrown; weak pavement blown off roads.
F4 Category Tornado
207-260 mph (180-226 kt)	Cat 5?	Devastating Tornado. Devastating damage: Well constructed homes leveled; structures with weak foundations blown off some distance; cars thrown and disintegrated; large missiles generated; trees in forest uprooted and carried some distance away.
F5 Category Tornado
261-318 mph (227-276 kt)	NA	Incredible Tornado. Incredible damage: Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile-sized missiles fly through the air in excess of 300 ft (100 m); trees debarked; incredible phenomena will occur.
F6-F12 Category Tornadoes
Gtr than 319 mph (277 kt)	NA	The maximum wind speeds of tornadoes are not expected to reach the F6 wind speeds.