Tornadoes and severe storms tornado heavy weather tiempo temps tempo wetter väder sää vær

Tornadoes form from severe thunderstorms. They have a very high energy density which means that they are very destructive to a small area. They also don't last very long which makes them hard to study. Without much information about how they develop, meteorologists have a hard time forecasting when they'll form. The general public knows even less about tornadoes, which is why there are so many inaccurate myths about them.

75% of the world's tornadoes occur in the United States, but they can (and probably have) developed anywhere. Most tornadoes in the U.S. form in an area of the Great Plains known as Tornado Alley. There are also some other interesting facts about tornadoes. People with an interest in tornadoes sometimes attend classes held by the National Weather Service and become spotters for their communtiy. Sometimes people travel out to Tornado Alley to chase tornadoes first hand! When a tornado touches down, scientists try and figure out how strong it was by using the Fujita Tornado Scale.

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Engergy

A tornado is the most destructive force in nature; that doesn't mean it has the most energy. Thunderstorms which produce tornadoes can have 40,000 times as much energy as a tornado! Tornadoes are so destructive because they have a higher energy density than thunderstorms; the energy is concentrated in a small area while the energy in a thunderstorm is spread-out over a much greater area.

Energy and energy density can be compared to weight and force. Energy density is energy per unit volume and force is weight per unit area. If a 100 pound person in flat shoes stepped on your foot, you'd feel it. If the same person stepped on your foot while wearing very narrow high-heels, you might end up with a broken toe. That's because the person's weight is concentrated in a small area. The same holds with tornadoes. They may not have as much total energy as thunderstorms, but the energy they do have is concentrated in a very small area. So small, in fact, that tornadoes have destroyed houses while not damaging the neighbors.

Tornado

Mesecyclone

Most tornadoes form in a part of a supercell thunderstorm called a mesocyclone. The mesocyclone draws energy into the storm so it can last for hours. Scientists aren't sure why, but some can create tornadoes. Mesocyclones can be detected by conventional radar as a hook echo. In the mesocyclone, air is drawn into the storm. Scientists believe a vertical wind sheer (wind that changes direction with height) causes the tornado to begin spinning. Most tornadoes spin cyclonically but a few spin anticyclonically. Strong fronts develop between cold polar air and warm tropical air and when the atmosphere is unstable tornadoes can form. Tornadoes form throught the year but most occur in May. Though, the most damage is usually caused in April which means that the more dangerous tornadoes form then. The more north you go, the later the main tornado season becomes. The atmosphere in the norther plains is cooler and more stable earlier in the year; it takes longer for the sunlight to heat it up.

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Forecast and detection

The short duration and complicated nature of tornadoes make them nearly impossible forecast. Meteorologists don't really know the specifics of how they form, but they do know what atmospheric conditions were present during past tornadoes. They use this knowledge to try and identify tornado threats before they happen. The earlier they realize that a tornado is going to strike, the earlier they can notify residents of the areas which will be hit. The more warning people have, the fewer people will be killed. To know the current atmosphere conditions, meteorologists send up weather balloons every twelve hours to take soundings of the upper atmosphere. The equipment on the balloons measure conditions such as the atmospheric stability, temperature, and relative humidity. Two conditions tornadoes need to form are high instability and a high dew point. When these conditions exist, they issue a tornado watch. A new type of weather radar can greatly improve the time between tornado detection and tornado touchdown. Conventional radar could only be used to detect a tornado after it had formed, usually by seeing a shape such as a hook echo on the radar return. The echo doesn't appear with every tornado, so forecastor can't rely on just that information. They also need observations from tornado spotters in order to issure a tornado warning.

Tornado strength scale

Before 1971, there was no way to categorize tornadoes by their strength. Because they're so intense, it's impossible to measure the wind speed or the pressure like you can do in a hurricane. Without a standard system to rank tornadoes, there was no way to keep an accurate storm record; everybody had their own idea of how strong the storm was.

T. Theodore Fujiata, a professor at the University of Chicago, came up with a system that equated wind speed with tornado damage. The scale Fujita came up with connects the Beaufort wind scale with Mach 1 in twelve steps. Tornadoes are only observed in categories F0 to F5. There could theoretically be an F6 tornado, but the damage would be so incredible that it would be nearly impossible to tell the difference between an F5 and an F6 tornado. Scientists have to figure out how strong a tornado was after it is over. Because the scale is based on the damage caused by it, they can't predict how strong a tornado would be before it strikes like they can predict a hurricane's strength using the Saffir-Simpson scale.

Photos of a Severe Thunderstorm in the The Netherlands on the 17th of July 2004

Bad weather in the netherlands: Severe Thunderstorm