What is a Tornado?
A Tornado also known as a twister is a amazingly destructive whirlwind that descends to the Earth from the womb of a thundercloud.
More Tornadoes occur in the United States than anywhere else on earth. From Nebraska to Texas, experience the most tornadoes. This area is called Tornado Alley.
How do Tornadoes form?
Cold air blowing southward from Canada frequently collides with warm, moist air moving northward from the Gulf of Mexico. These conditions are perfect weather for a thunderstorm or tornado.
How do you know if a Tornado is coming ?
One sign is that they usually occur after a thunderstorm. If you see a cumulonimbus cloud there might be a Tornado.
Do you know what warnings to look for?
When there is a warning about a tornado the call it a "tornado warning".
Are there precautions you can take and are there scales to tell how bad there are?
Yes there are precautions you can take like getting in a basement and getting away from windows. Also there are scales like the one below.
Time Lapse of the 05-27-15 Canadian Texas Tornado