Scientists rank a tornado's intensity and estimate its wind speed based on observed damage, using a scale developed by the late University of Chicago researcher Tetsuya Theodore Fujita:
 |
Click on tornado to hear Dr.Fujita.
F0: Gale tornado.
Wind speed: 40-72 mph. Damage: Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.
F1: Moderate tornado.
Wind speed: 73-112 mph. Damage: The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.
F2: Significant tornado.
Wind speed: 113-157 mph. Damage: Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.
F3: Severe tornado.
Wind speed: 158-206 mph. Damage: Roof and some walls torn off well-constructed houses; trains overturned; most trees in forests uprooted.
F4: Devastating tornado.
Wind speed: 207-260 mph. Damage: Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown; large missiles generated.
F5: Incredible tornado.
Wind speed: 261-318 mph. Damage: Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile-sized missiles fly through the air in excess of 100 meters; trees debarked; steel-reinforced concrete structures badly damaged.
On average, only one F5 tornado hits the United States each year. F5 twisters struck in 1999 in Norman, Ok.; 1998 in Waynesboro, Tenn., and Pleasant Grove, Ala.; in 1997 in Jarrell, Texas; in 1996 in Oakfield, Wis.; in 1992 in Chandler, Minn.; and in 1990 in Plainfield, Ill., Goessel, Kan., and Hesston, Kan. In one of the worst U.S. tornadoes on record, seven F5s struck the Midwest on April 3, 1974, including at Xenia, Ohio. F6: Although he called it ''inconceivable,'' Fujita left open the possibility a tornado could cause a small area of damage even worse than F5 intensity. But he said evidence of an F6 tornado - with wind speed up to 379 mph - likely would be masked by damage from surrounding F4 and F5 wind
How tornadoes form
The ingredients to form a tornado are: a big thunderstorm; winds blowing from opposite directions; and a strong updraft. Strong updrafts surge up through storm clouds causing the cloud tops to bubble up and subside. A tornado can form when the air in these updrafts begins to rotate as opposing winds cause the storm to start spinning. This whirling mass of air and cloud is called a vortex and the spinning column of air within the vortex is called a mesocyclone. The air pressure in the center of the vortex drops as more air is sucked into it, although at the present time scientists do not know just how low the air pressure can get within the center of the vortex. As the mesocyclones get stronger they begin to shrink and spin faster. The familiar funnel shape of a tornado develops as the air pressure in the center of the vortex drops. As more and more air gets drawn into the funnel it accelerates upwards and the funnel stretches.
See what the weather is like outside.
Tornado Watches and Warnings
A tornado watch means that weather conditions will support the formation of a tornado and a tornado may occur in your area. Listen to local radio/television, or NOAA Weather Radio for information and advice. A tornado warning means that a tornado has actually been sighted or has been indicated by radar and may strike your vicinity. Take action to protect yourself from being blown away, struck by falling objects, or injured by flying debris.
Safety and Preparedness Tips
If a tornado warning is issued for your location, take the following steps immediately. These steps should also be practice during your tornado drills. Go at once to the basement, storm cellar, or the lowest level of the building. If there is no basement, go to an inner hallway or a smaller inner room without windows, such as a bathroom or closet. Get away from the windows. Go to the center of the room. Stay away from corners because they tend to attract debris. Get under a piece of sturdy furniture such as a workbench or heavy table or desk and hold on to it. Use arms to protect head and neck. If in a mobile home, get out and find shelter elsewhere The designated tornado shelter should always be stocked with the following disaster supplies: Flashlight and extra batteries Portable, battery-operated radio with weather band and extra batteries First aid kit and manual Emergency food and water Nonelectric can opener Essential medicines Cash and credit cards Sturdy shoes
Watching the skys for a twister.This picture is from the first tornado preparedness film.
Safety Tips Away From Home Tornadoes often strike when people are in unfamiliar surroundings, whether it is a car, a building, or a park. Here are several steps you can take if a tornado threatens when you are away from home. If at work or school: Go to the basement or to an inside hallway at the lowest level. Avoid places with wide-span roofs such as auditoriums, cafeterias, large hallways, or shopping malls. Get under a piece of sturdy furniture such as a workbench or heavy table or desk and hold on to it. Use arms to protect head and neck. If outdoors: If possible, get inside a building. If shelter is not available or there is no time to get indoors, lie in a ditch or low-lying area or crouch near a strong building. Be aware of the potential for flooding. If in a car: Never try to outdrive a tornado in a car or truck. Tornadoes can change direction quickly and can lift up a car or truck and toss it through the air. Get out of the car immediately and take shelter in a nearby building. If there is no time to get indoors, get out of the car and lie in a ditch or low-lying area away from the vehicle. Source: Federal Emergency Management Agency
How about some music?
Click on the young lady
Questions & Answers
*How long do tornadoes last?
Most tornadoes last only two or three minutes. The kind that we see in videos and the kind that do the damage we see on the news probably average about 15 minutes.
*What is the longest continuous tornado track in recorded history?
The track of the Tri-State Tornado is officially 219 miles, and stands as the record. However, the concept of tornado families was not known in 1925, and this may have been a family of several tornadoes.
*How fast do tornadoes move?
The few tornadoes that have been timed seem to average about 35 miles per hour, but every year some are seen to stand still and others are clocked at 60 miles per hour.
*Do they ever occur in the mountains?
Tornadoes have occurred in every kind of terrain. In 1987, one may have crossed the Continental Divide in Wyoming's Teton Wilderness. They are rare in mountainous areas, but a well developed tornado is probably not affected by the shape of the land underneath it.
*How big in diameter do tornadoes get?
Tornadoes have been known to range in diameter from 3 feet to two miles. The last one recorded to be 2 miles wide was seen near the town of Gruver in the Texas Panhandle on June 9, 1971. These giant ones, however , generally don't have high wind speeds.
*Okay,so if trailers don't attract tornadoes, why do so many trailer parks get hit by tornadoes?
There are probably hundreds(maybe more than a thousand) very small tornadoes that touch down in the USA every year, but are not recorded because they do no damage. However, since a mobile home flips over so easily in even the weakest tornado, trailers probably act as "mini tornado" detectors.
*How strong a wind does it really take to blow over a mobile home?
Lightweight mobile homes can be flipped by a 60 mile per hour wind. Heavier mobile homes may not go until 70 or 80 miles per hour. And a tied down trailer might stay put at 110 miles per hour.
*Where is Tornado Alley?
There are several areas that can be considered "Tornado Alley". The area from central Texas to Colorado, North Dakota and Minnesota commonly gets this poorly defined label. But there is also a tornado-prone area that extends eastward from Texas to Georgia that can be considered as a Tornado Alley, and still another "alley" from Arkansas to the Ohio River and the Great Lake states of Ohio, Indiana, Illinois and Michigan.
*Are there places that are not in Tornado Alley that still get more than the average number of tornadoes?
Florida gets more small tornadoes per square mile than any other state, but so few big ones that most people don't consider it as a "tornado alley". Southern New England seems to have its own little "tornado alley" in western Massachusetts and Connecticut.
*Do they really get tornadoes in California?
California is a very large piece of real estate, with all kinds of curves on the coast, mountains and a huge central valley. With such a varied terrain, storms and air flow conditions manage to create conditions for small and weak tornadoes every year. Tornadoes are certainly not new to California, but despite the high population, no one has ever been killed by one.
*How about Hawaii?
Quite a number of waterspouts have come ashore in Hawaii and have been damaging to resorts. Those are counted as tornadoes.
*Which way do tornadoes turn?
Cyclonically, of course! Tornadoes turn counterclockwise in the northern hemisphere. Warm air sweeps north, jet streams come in from the west, creating a situation in which the storms rotate counterclockwise. The tornadoes usually rotate that same way. Sometimes opposite direction swirls develop under a thunderstorm. And about 1 in 100 tornadoes rotate clockwise. The situation is just the opposite in the southern hemisphere(well, not quite the opposite, but close)
| |||||||||||||||||||||||||
Weather Links:
Visit my favorite tv channel
A great tornado site.
Enjoyable site with good graphics.
A very informative site.
This site has it all.
There's No Place Like Home
