Tornadoes in america

Investigation of an extraordinary natural phenomenon

Every year, about 60 people are killed in the United States by tornadoes. A common meteorological event in the country, devastating, which remains difficult to explain and whose origin is uncertain. Why are there more tornadoes here than elsewhere? How does a tornado form and, above all, can we anticipate it? We tell you everything (what we know).

Tornado OB A.BA

What is a tornado?

A tornado is a natural phenomenon which appears as a rotating funnel-shaped cloud that extends from a thunderstorm to the ground with swirling winds up to 500 km per hour. Some tornadoes are clearly visible, while nearby rain or low clouds obscure others.

The difference between a hurricane and a tornado

Tornadoes always form on land while hurricanes form in the oceans. The wind speed of a hurricane rarely exceeds 250 km/h, that is, almost 2 times less than that of a tornado. Also, the diameter of a tornado is significantly smaller (400 meters) than that of a hurricane that can reach 1500 km! Finally, the lifespan of a tornado is a few minutes, while that of a hurricane can be active for several weeks.

How does a tornado form?

For a tornado to form, it needs the right mix of ingredients at the right time: warm, moist air close to the ground, cold air higher in the atmosphere, and superimposed wind moving at different speeds or directions. In fact, few places on Earth meet all these conditions, except for the region of great plans — and particularly the states of Texas, Missouri, Kentucky, and Oklahoma. It is also called “Tornado Alley“. As warm air rises from the Gulf of Mexico, it creeps north across the plains. Where is the air that blows west of the American Rockies.

When the two winds meet, they can create a wind vortex that rotates horizontally. The tornado is formed.

Tornado classification: the Fujita scale

Not all tornadoes are the same and their intensity varies significantly.
Dr. T. Theodore Fujita of the University of Chicago in 1971 created a measurement system analyzing the wind speed of tornadoes on the F0-F5 scale according to the damage caused. L’Echelle, improved over the years, has become The Enhanced Fujita Scale in 2007 (EF). Overall, 77% of tornadoes in the United States are considered weak (EF0 or EF1) and approximately 95% of all tornadoes in the United States are less than EF3 in intensity. The remaining small percentage of tornadoes are classified as severe (EF3 and above). Finally, among these violent tornadoes, only a few reach EF5 status.

Can a tornado be avoided?

Although it is extremely difficult to announce a tornado in advance (on average 15 minutes before), some signs suggest that this storm could be unleashed: a dark sky with sometimes large greenish or yellowish clouds hail and large, dark, low clouds that swirl and form a funnel.
On a larger scale, new systems that take into account the instability of the atmosphere, the rate of humidity, temperature and wind shear (the difference in speed and direction depending on altitude), both data provided by weather radar or satellites and images help meteorological experts predict the risk of tornadoes.

the official website of National Weather Service provides detailed information about the tornado phenomenon and the safety tips to protect yourself.

incomprehensible numbers

  • Tornadoes have landed on every continent on Earth except Antarctica.
  • In average, 1,200 tornadoes hits the United States every year.
  • Also every year, tornadoes cause 70 deaths and 1,500 injuries.
  • In Oklahoma, the tornado capital of the worldtornadoes only hit the same location once every 1,200 to 1,500 years, on average.
  • The deadliest tornado hit Bangladesh in 1989. It left 300 dead and 12,000 injured.
  • Spring 2011 was America’s deadliest tornado season, with more than 580 people killed between April and June. The damage bill increased to $21 billion.
  • Tornadoes can follow tropical storms and the hurricanes as they move towards the ground.
  • Funnel clouds usually last less than 10 minutes before dissipating, and many last just a few seconds.
  • The peak of tornado season in the southern states is from March to May; in the northern states, it is from late spring to early summer.
  • Historically, May is the most active month for tornadoes, with an average of 276 tornadoes occurring each year in the United States, reports NOAA.
  • Tornadoes are most likely to occur between 3pm and 9pm, but they can occur at any time.

“Dominator” – Tornado interception vehicle. Credit: Hydrargyrum

Job ? tornado chaser

Those extreme adventurers crossing the Tornado Corridor (Tornado Alley), in search of photos of a very photogenic tornado, are real stars in the United States and even have their own television show. The most known and recognized tour in a “dominant“, a vehicle transformed into a tank, with armored windows and tested in the explosion of aircraft. This increasingly sophisticated equipment does not protect against tragedies, unfortunately, several tornado chasers have died in recent years, in particular. Tim Samaras killed by the El Reno tornado in 2013.

Leave a Comment