When is a tornado officially labeled as a tornado?
A tornado is a tornado when there is a violently rotating column of air that is in contact with both the ground and a type of cloud above it.
A tornado is a tornado when there is a violently rotating column of air that is in contact with both the ground and a type of cloud above it. The definition does not require a funnel cloud nor any particular speed of rotation. Check out the Definition section in the wiki article below:
The Fujita Scale is used to rate tornados and the damage they cause (there is an updated one that came out in 2007 with a lot more detail to it than necessary for this answer - but know that it is out there). The original scale is here:
Developed in 1971 by T. Theodore Fujita of the University of Chicago
#color(blue)("Scale ") -> color(purple)("Wind Estimate mph ") -> "Typical Damage"# #color(blue)("F"0):" "color(purple)(< 73) ->#Light damage
Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.
#color(blue)("F"1):" "color(purple)(73-112) ->#Moderate damage
Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.
#color(blue)("F"2): " "color(purple)(113-157) ->#Considerable damage
Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
#color(blue)("F"3): " " color(purple)(158-206) ->#Severe damage
Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
#color(blue)("F"4): " " color(purple)(207-260) ->#Devastating damage
Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.
#color(blue)("F"5):" " color(purple)(261-318) ->#Incredible damage
Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.
IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified.
Different wind speeds may cause similar-looking damage from place to place -- even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.
The Enhanced F-scale will be implemented February 2007.
And here's a video with details about tornado speeds, damage, etc...