A monstrous, black funnel descends from the sky winding its way over the ground, utterly indifferent to every living thing in its path. In fact, a tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. With most violent tornadoes capable of tremendous destruction and wind speeds of 250 mph or more, they are truly nature’s most violent wind. The path of destruction from a tornado can be in excess of one mile wide and 50 miles long. There have been tornadoes with wind speeds up to 300 miles per hour!! Once a tornado in Broken Bow, Oklahoma, carried a motel sign 30 miles and dropped it in Arkansas! Fortunately, speeds this high are very rare, occurring in only 2% of tornadoes. A similar phenomenon to tornadoes is a funnel cloud, which is simply a tornado that does not touch down.
Although tornadoes occur in many parts of the world, these destructive forces of nature are found most frequently in the United States east of the Rocky Mountains during the spring and summer months. In an average year, 800 tornadoes are reported nationwide, resulting in 80 deaths and over 1,500 injuries. A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground.
The simplest explanation for what causes tornadoes is the rapid convection of air. A good analogy to explain how convection works would be water in a pot on the stove; the water at the bottom heats first since it's closer to the heat source, causing the water molecules in the hotter area of the pan near the bottom to accelerate. Then they bombard the other, cooler water molecules and set them in motion upward through the water column. This causes the differing water temperatures in the pot to circulate around inside (without ever having to stir it with a spoon!).
The same conditions happen in the air in the lower and upper atmosphere. When very warm, humid air that is close to the ground continues to heat up from the heat rising off the ground it rises upward rapidly towards superheated, dry air that is forcing that air down towards the ground. Think of the warm, humid air layer above the ground as starting to "boil" and push its way upward. When it rapidly breaks through the mid-to-upper layer of stable, dry air into the cooler, moist air of the upper atmosphere, those rapidly moving air molecules pick up speed, forcing the air currents to flow downward rapidly. This reaction happens very quickly and gains momentum as the wind shear increases. Typically, the rotating column of air begins parallel to the horizon, but then swings down and touches the ground. This is when it becomes painfully visible to all because the dirt, dust and debris the twister is picking up, colors the column black.
It's kind of hard to imagine that something so small and invisible to the human eye - air molecules - could move with such tremendous energy and cause such a gigantic wind phenomenon.
During the spring in the Central Plains, thunderstorms frequently develop along a "dryline," which separates very warm, moist air to the east from hot, dry air to the west. Tornado-producing thunderstorms may form as the dry line moves east during the afternoon hours.
Along the front range of the Rocky Mountains, in the Texas panhandle, and in the southern High Plains, thunderstorms frequently form as air near the ground flows "upslope" toward higher terrain. If other favorable conditions exist, these thunderstorms can produce tornadoes.
Tornadoes occasionally accompany tropical storms and hurricanes that move over land. Tornadoes are most common to the right and ahead of the path of the storm center as it comes onshore. (Blanchard, 2009)http://extremescience.com/tornado.htm
When a tornado happens over water, the tremendous power of the upward draft through the center of the cyclone causes a sucking action (like a vaccuum), which draws water up inside creating a water spout. These can travel over water onto dry land, turning into a tornado.
Waterspouts
· Waterspouts are weak tornadoes that form over warm water.
· Waterspouts are most common along the Gulf Coast and southeastern states. In the western United States, they occur with cold late fall or late winter storms, during a time when you least expect tornado development.
Waterspouts occasionally move inland becoming tornadoes causing damage and injuries (Golden, 2009) nssl.noaa.gov/edu/safety/tornadoguide.html
Tornado Safety
There is no such thing as guaranteed safety inside a tornado. Freak accidents happen; and the most violent tornadoes can level and blow away almost any house and its occupants. Extremely violent tornadoes are very rare. Most tornadoes are actually much weaker and can be survived using these safety ideas...
Prevention and practice before the storm: At home, have a family tornado plan in place, based on the kind of dwelling you live in and the safety tips below. Know where you can take shelter in a matter of seconds, and practice a family tornado drill at least once a year. Have a pre-determined place to meet after a disaster. Flying debris is the greatest danger in tornadoes.; so store protective coverings (e.g., mattress, sleeping bags, thick blankets, etc) in or next to your shelter space, ready to use on a few seconds' notice.
In a house with a basement: Avoid windows. Get in the basement and under some kind of sturdy protection (heavy table or work bench), or cover yourself with a mattress or sleeping bag. Know where very heavy objects rest on the floor above (pianos, refrigerators, waterbeds, etc.) and do not go under them. They may fall down through a weakened floor and crush you.
In a house with no basement, a dorm, or an apartment: Avoid windows. Go to the lowest floor, small center room (like a bathroom or closet), under a stairwell, or in an interior hallway with no windows. Crouch as low as possible to the floor, facing down; and cover your head with your hands. A bath tub may offer a shell of partial protection. Even in an interior room, you should cover yourself with some sort of thick padding (mattress, blankets, etc.), to protect against falling debris in case the roof and ceiling fail.
