Tornadoes

A tornado is a rotating, funnel shaped cloud that is in contact with the cloud base and the ground. Wind speeds in a tornado can reach up to 300 miles per hour, though many do not. They can cause damage over one mile wide and 50 miles long. Tornadoes are not, necessarily, visible. It becomes visible when the winds inside the funnel lift up dirt and debris from the ground. Some tornadoes can be "hidden" by the rain from the thunderstorm or by low-hanging clouds. A tornado ends when its energy source is gone. It needs a source of instability, like heat or moisture, and a larger area of rotation. It it loses either of these, the tornado will dissipate.

Tornadoes are rated on the Enhanced F-Scale. The original F-Scale was named after Dr. T. Theodore Fujita who developed the scale. It was changed some, since the original scale was untested. The Enhanced F-Scale took effect on February 1, 2007. Both scales rate a tornado as a whole based on the most intense damage that the tornado did.
A F-0 tornado is a Gale Tornado with winds about 40 to 72 MPH. It can damage chimneys, break branches off of trees, and uproot shallow-rooted trees.
A F-1 tornado is a Moderate Tornado with winds about 73 to 112 MPH. It can peel off roof surfaces, push mobile homes off their foundations or overturn them, and it can push moving cars off the road.
A F-2 tornado is a Significant Tornado with winds 113 to 157 MPH. It can tear a roof off a frame house, demolish a mobile home, snap or uproot large trees, and create projectiles from light objects.
A F-3 tornado is a Severe Tornado with winds 158 to 206 MPH. It can tear a roof and some walls off a well-constructed house, overturn a train, and lift up and throw heavy cars.
A F-4 tornado is a Devastating Tornado with winds about 207 to 260 MPH. It can level well-constructed houses, move structures with weak foundations, and create large projectiles.
A F-5 tornado is an Incredible Tornado with wind speeds about 261 to 318 MPH. It can lift up and carry strong frame houses, create projectiles the size of a car and throw it over 100 yards, and debark a tree. The complete F-Scale is at FEMA Kids Intensity Scales.

A tornado can form anywhere in the world. In the United States, every state is at risk for a tornado, but Tornado Alley has the highest risk. Tornado Alley consists of the states: Arkansas, Iowa, Kansas, Louisiana, Minnesota, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, and Texas. A tornado can form at any time during the year, but they are most common during the tornado season, which is from March to August. The peak tornado season for the southern states is in the spring, while it is during late spring to early summer for the northern states. Tornadoes can occur at any time, day or night, though most occur in the late afternoon and evening, between the hours of 3 and 9pm. A tornado typically moves from southwest to northeast, though it can travel in any direction. Some tornadoes will even change direction at any time, or even backtrack suddenly. There is no way to know when, or if, a tornado will change direction, so it is best to stay inside in a safe place.

When a tornado is coming you need to take shelter right away. You should move to an interior room, or basement, and stay away from any windows. If you are in a basement, try to get under some sort of sturdy structure, like a work bench. If that is not possible, cover yourself with a mattress or sleeping bag. You want to be protected from falling debris. Also, if you are in a basement, you want to try to stay out from under heavy objects that are on the floor above you, like your fridge. If you do not have a basement you should get to a room that has no windows in the center of the building. Good places are bathrooms, closets, under a stairwell, or in an interior hallway. You should crouch down as close to the floor as possible and cover your head with your arms. You should also have something soft, like a mattress or sleeping bag, to cover yourself with. If you are in a mobile home, you need to get out of it. Your chances are better laying in a ditch than if you stay in your mobile home. If you can get to a shelter, that is where you should go. If you cannot get to a shelter you should lie flat on low ground as far away from your mobile home, cars and trees as you can get, and remember to cover your head. If you are in a car, and the tornado is far away, you may be able to drive out of the path of it by driving at right angles to the tornado. If the tornado is too close to get away from it, you need to get out of your car and seek shelter in a sturdy building, if possible. If there are no sturdy buildings around, you should run to low ground, away from any cars, and lie flat on the ground covering your head. FEMA has a table with what to do during a tornado.

Myth: You should open your windows when a tornado is coming.

Fact: This should not be done because it doesn't do anything and wastes precious time. A tornado will blow the windows open for you. The time is better spent getting yourself, and family, to a safe place.

Myth: The southwest corner is the safest spot in your basement.

Fact: People believe this because most tornadoes move from the southwest to the northeast. Being in the southwest corner is no safer than any where else because the tornado can blow debris in any direction.
Another myth is that areas near rivers, mountains, and lakes are safe from tornadoes. A tornado can form anywhere at anytime.

Waterspouts are tornadoes that form over water. These tornadoes are just as dangerous as a land tornado and can move onto land at anytime. A waterspout can form over seas, bays and lakes. They do not count in the tornado records unless they hit land. Waterspouts can overturn boats, damage ships, and do significant damage if they hit land.

FEMA for Kids
FEMA
Online Tornado FAQ
Tornado Safety
Live Science
American Red Cross
Pictures from NOAA Photo Library