How strong does a tornado have to be to be considered "significant"?

Tornadoes that are EF2 or stronger are generally considered to be significant in scale. EF4 and EF5 tornadoes are considered "violent," and rightly so!

How many F5 tornadoes have there been in the United States since 1970?

There have been 28 F5 tornadoes in the United States since 1970. Six of these occurred during the tornado outbreak of April 1974.

F5 Tornadoes in the United States, 1970-2008

What is a turtle?

In terms of meteorology, the word turtle does not refer to a shelled reptile. Rather, they are sturdy encased instruments that can be placed in the path of a tornado to measure air pressure, humidity, and temperature. Unfortunately, they cannot measure wind speeds, but they do gather this other valuable data.

Has there ever been an F6 tornado?

No. Although the old Fujita Scale did allow for an F6 tornado (estimating that winds up to 380 miles [611 kilometers] per hour were theoretically possible), there has been no recorded tornado of that intensity. The EFS does not include an F6 category at all, and lists any tornado with winds over 200 miles (320 kilometers) per hour as an F5.

Do meteorologists actually have reliable data on tornado wind speeds?

No, and that is a big part of the problem in categorizing tornadoes. Tornado wind speeds have been scientifically estimated using Doppler radar and video observations, but there have been no successful attempts to physically measure speeds using an anemometer.

What is the VORTEX project?

VORTEX stands for Verification of the Origin of Rotation in Tornadoes Experiment. Conducted at the National Severe Storms Laboratory from 1994 to 1995, the project was led by Erik Rasmussen, and the goal was to conduct intense data gathering using weather balloons, air planes, turtles, and cars equipped with radars and taking photographs. The study focused on tornadoes formed in supercells and collected so much data that it took years to analyze it all.

How long a path do tornadoes typically make?

Most tornadoes actually have fairly brief lifespans, lasting less than an hour and often only several minutes or seconds. About five miles of travel can be expected from an average tornado. Of course, there have been much longer-lived tornadoes, such as one on March 18, 1925, which crossed 215 miles (346 kilometers) of terrain.

What is a multiple-vortex tornado?

Sometimes a central tornado can be surrounded by smaller tornadoes called sub-vortices or suction vortices. There can be as many as seven subvortices surrounding the central tornado, though two to five is more common. Interestingly, these smaller tornadoes tend to be more intense, with winds spinning at about 100 miles (160 kilometers) per hour or more faster than the central vortex.

A wind speed instrument mounted on a Project Vortex vehicle monitors conditions in northern Texas in this 1994 photo. (NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory)