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TORNADOES


Most tornadoes occur east of the Rocky Mountains to the east coast of the U.S. They usually occur during the spring and summer months. Each year tornadoes cause an average of 80 deaths and 1,500 injuries.




What is a Tornado?

A tornado is a violently rotating column of air that extends from a thunderstorm to the ground. Tornado winds can reach 250 miles per hour or more. Strong tornadoes can cause damage paths up to one mile wide and 50 miles long! According to Wikipedia, tornadoes have been seen on every continent except Antarctica. The United States has the most tornadoes in the world and most of those occur in what is known as "Tornado Alley" which includes the Great Plains, South and Midwest regions of the United States




Funnel Cloud:

Many times the first visible sign of a tornado is a funnel cloud. A funnel cloud is a rotating cloud below a larger cloud with no strong winds at ground level. As a tornado forms, the funnel cloud will stretch downward toward the ground.

Funnel Cloud
Funnel Cloud




Tornado Characteristics:

Size and Shape:

Some tornadoes are shaped like a cylinder and are lower to the ground, those are called a "stovepipe." Others and called "wedges" because they look like wedge stuck into the ground. A third type of tornado shape is a "rope" tornado that actually looks like a extending from the clouds to toward the ground.

Stovepipe Tornado
Stovepipe Tornado

Wedge Tornado
Wedge Tornado
Rope Tornado
Rope Tornado



















Types Of Tornadoes:


Tornadoes come in various sizes and can form in different locations and under different types of weather conditions. Below are some of the variations.

Super-cell Tornadoes

Some of the strongest and most damaging tornadoes develop from supercell thunderstorms. A supercell thunderstorm is a long lasting thunderstorm that has a rotating updraft of air. These storms are the most likely to produce tornadoes. The supercell thunderstorm has a low-hanging, rotating layer of cloud known as a “wall cloud.” It looks a lot like a layer of a layer cake that hangs below the cloud base. One side of the wall cloud is often rain-free, while the other side may be surrounded by heavy rain. The tornadoes that come from supercell thunderstorms are more likely to remain in contact with the ground for long periods of time -- an hour or more - than other tornadoes, and are more likely to be violent, with winds over 200 mph.

Waterspout

A waterspout is a tornado over water. A few form from supercell thunderstorms, but many form from weak thunderstorms. Waterspouts are usually less intense and cause a lot less damage than supercell tornadoes. They are not usually more than fifty yards wide, and they form over warm tropical ocean waters. Even though waterspouts form over ocean waters, their funnel is made of freshwater droplets condensed from water vapor from condensation - not saltwater from the ocean. Waterspouts usually die out when they reach land.

Land spout

Land-spouts are also weaker than a supercell tornado and landspouts are not associated with a wall cloud. Landspouts are the land equivalent of a waterspout. They often form along the leading edge of a rain-cooled downdraft of air that comes from a thunderstorm, known as a gust front.

Dust Devils
Dust devils are like cousins to tornadoes. Dry, hot, clear days on the desert or over dry land can bring about dust devils. It isn't unusual to see dust devils in open fields here in Illinois. They generally form in the hot sun during the late morning or early afternoon hours. They are mostly harmless whirlwinds that are triggered by light to moderate breezes that create a swirling column of dust with speeds about 70 mph. These differ from tornadoes in that they are not associated with a thunderstorm (or any cloud), and are usually weaker than the weakest tornado. Usually, the life cycle of a dust devil is a few minutes or less, although they can last longer. Although usually harmless, they have been known to cause minor damage. They can blow vehicles off the road and could damage your eyes by blowing dust into them.







Appearance:

Tornadoes can take on very different appearance depending on the specific weather conditions and environments that they form in. Some tornadoes take on lots of dirt and debris which makes them darker. Other tornadoes can be more gray or white because they haven't picked up much debris. Tornadoes traveling over water can turn white or even blue due to the water that they pick up. The time of day that a tornado occurs also has an effect on the way it looks. Tornadoes with the sun behind them will look darker and night-time tornadoes might only be seen when lightening flashes.

Sun Behind Tornado
Sun Behind Tornado
Night-Time Tornado
Night-Time Tornado
















Rotation:

According to Wikipedia, tornadoes rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.



Tornado Sounds:

People who have been in or close to tornadoes often say that they sounds like a freight train, a waterfall or possibly even a jet engine. The high winds create a loud roaring sound. The tornado sound is influenced by how far away it is and by the type of land that it is passing over (flat, hilly, etc). As the tornado picks up debris and as the conditions in air pressure change, the tornado sounds can also change.


Measuring the Intensity of a Tornado:

The strength of tornadoes are rated using the Fujita Scale. Weather experts use the Fujita scale to rate wind speed and estimate damages. The fujita scale isn't as concerned with the shape, size or location of a tornado, it is focused on the actual intensity of the tornado.



external image enhanced_fujita_scale.gif





Tornado Detection:

Tornado detection in the United States has come a long way in the last 50 years. Before the 1950's, the only way that a tornado could be detected was when it was sighted on the ground. Then during the 1950's weather radar was invented and it was possible for local weather offices to warn the public that severe weather was a possibility. In 1953 it became possible for meteorologists to detect thunderstorms that were capable of producing tornadoes while they were still 50 or 60 miles away. Today, meteorologists are able to use dopple radar to detect storms that can produce tornadoes. Doppler radar can measure the strength and direction of winds in a storm from more than 100 miles away. Another more simple method of detection is to use storm spotters. Spotters are trained people such as local police and fireman who look out for severe weather and call in reports of any severe weather that they see.





Tornadoes in the United States:

North America has unusual geographical features that make the middle and southern regions of the United States prime areas for tornadoes to form. The United States has both tropical and arctic climates, but what has the most influence on tornado formation is the combination of the Rocky Mountains in the Western U.S. and the warm moist air from the Gulf of Mexico. The Rocky Mountains cause the air to become colder and dryer as it passes over them. That air collides with the warm, moist air from the Gulf and the result is often severe thunderstorms and sometimes tornadoes. Spring and fall are the seasons when the most tornadoes occur. The reason for that is because there are stronger winds and the atmospheric conditions are less stable during those times. Tornadoes are also more likely to occur during the late afternoon and early evening because of solar heating. However, tornadoes can and have occurred at any time during the day or night. Nighttime tornadoes and winter tornadoes are the deadliest because they often catch people off-guard and unprepared.



What causes a Tornado?

Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an
invisible, horizontal spinning effect in the lower atmosphere.


Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.



external image pic6.gif
An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within
this area of strong rotation.






Tornado Myths & Facts:

Myth One: You should open the windows to lessen the pressure and decrease the damage caused by a tornado.
Fact: A strong tornado will destroy a house whether the windows are open or not.

Myth Two: Highway overpasses are safe places to go to get shelter from a tornado.
Fact: Highway overpasses are actually a dangerous place because they create a wind tunnel effect.
Myth Three: The southwest corner of a basement is that safest place to go during a tornado.
Fact: The opposite corner of the basement from the direction that the tornado is coming from is the safest area. Taking cover under a sturdy piece of furniture can also increase your safety.
Myth Four: There are some places that are protected from a tornado such as near major river, in a city, on a hill, etc.
Fact: There is no safe area from tornadoes, but some areas are more affected than others.





Tornado Safety:

The best way to survive a tornado is to go to the basement or an interior first-floor room of a sturdy building. Many public buildings have storm shelter areas where people can go to when severe weather hits. If traveling in a car, it is recommended that you get out of the car and find a sturdy shelter. If none is available, you should lay flat in a ditch.



Tornado Damage Video








Sources:

http://en.wikipedia.org/wiki/Tornado

http://www.nssl.noaa.gov/edu/safety/tornadoguide.html

http://www.sciencedaily.com/releases/2005/04/050411100716.htm