Fujita Scale

Intensity of tornadoes

Tornadoes are formed when the cumulonimbus bodies of warm and cold air meet. The contrasts in temperature cause the severe weather in twisting large cloud masses slowly on itself. Is created inside the cloud of upward movements of air that can reach impressive speeds. The Fujita scale is used to estimate the intensity of a tornado. The Fujita scale, or Fujita-Pearson scale, is a scale that ranks tornadoes by severity, depending on the damage they cause. The Fujita Scale was created in 1971 by the American researcher Tetsuya Theodore Fujita, meteorologist in collaboration with Allan Pearson, the Storm Prediction Center (forecast severe thunderstorms) in the United States. It was immediately adopted by the scientific community and weather.
- The force F0 is light winds from 60 to 120 km/h. The damage observed are broken branches, the deformation of signs, television antennas twisted...
- The force F1 is moderate winds from 120 to 180 km/h. The damage observed are torn tiles, trailers overturned...
- The force F2 is strong winds ranging from 180 to 250 km/h. Damage is observed, trees and roofs torn off...

- The force F3 is winds from 250 to 330 km/h. The damage is observed, walls and roofs of buildings into the air, forests cut down...
- The force F4 corresponds to wind speeds of 330 to 420 km/h. The damage observed is, buildings without foundations and vehicles overturned...
- The F5 is extreme winds ranging from 420 to 510 km/h. The damage is observed, buildings razed, trains moved...

NB: The Fujita scale does not take into account the quality of construction of damaged structures. That foundations were swept class systematically, a tornado in the category F5. Numerous studies have shown that the Fujita scale overestimates the wind speed in the categories F3, F4 and F5. For these reasons a new and improved version was created by the U.S. National Weather Service in 2006 and is now based on 28 indicators of damage, taking into account the types of buildings or structures. The Enhanced Fujita Scale, or EF is a rating scale of the strength of tornadoes by damage. It is used in the United States since the summer of 2007.

Image: More than 1 200 tornadoes develop each year in the United States, twenty reached levels 4 or 5 of the Fujita scale.

Enhanced Fujita Scale

- EF0: Parties partially removed roof (tile, shingles), gutters, chimneys and damaged cladding...
- EF1: Parties roof completely removed, soaring exterior doors, windows and broken windows...
- EF2: Roofs blown onto moving solid houses, houses completely destroyed, large trees broken or uprooted...
- EF3: Floors of solid destroyed houses, trains overturned, debarked trees, cars raised...
- EF4: well-built houses, houses blown cars and light frame, many objects become missiles...
- EF5: Homes razed and solid objects the size of a car are sucked into the air...
Wind speeds in a tornado can reach 500 km / h. The record was recorded by a tornado that passed through Missouri, Illinois and Indiana some 350 km on 18 March 1925. Rated F5 on the Fujita scale, the results of this tornado was disastrous (695 dead, 2,027 injured and three cities were partially destroyed). This is Florida knows that the greatest number of tornadoes, though most are of low intensity.
Oklahoma undergoes the greatest number of destructive tornadoes, but the largest number of U.S. tornadoes occur in Texas.

Image: The "Tornado Alley" in the United States (in pink). The cold continental air coming from the West, mingles with the most hot and dry Sonoran Desert of the southwestern United States air and the hot and humid coming from the Gulf of Mexico. The whole gives an unstable air mass that develops powerful storms and tornadoes. Image credit: public domain.

Tornadoes

Image: Aerial view of the destruction of the city of Moore after the passage of the tornado that hit the area south of Oklahoma City, Monday, May 20, 2013. This image shows the extent of damage that can cause EF5 tornado on the Fujita scale as it passes over the houses. The winds of the storm reached 320 km / h, crushing the houses that were on their way. We note here through the enlarged picture, and a trail of debris from both sides just a few meters, the rows of houses spared. Image Credit: CNN