Differences Between a Tornado "Watch" and a "Warning"

The feature article in the USA Weekend from Sunday, June 10th 2007, titled "Take our exclusive Weather Quiz" written by Stu Ostro of the Weather Channel was a very interesting piece to go through as it dealt with some facts and myths associated with weather.

I guess that ever since the movie "Twister" came out (I still watch it every time it is on) I have been a little curious about tornadoes, and the section about tornado safety caught my attention because it got me wondering what do people really know about tornadoes, so I decided to do a little research on some things I have wondered about tornadoes and see if anyone else might find it interesting.

Tornadoes occur most frequently in the United States, in an area called "tornado alley" in the spring and early summer. Tornado alley is vulnerable because of its unique geographic characteristics. As cool, dry air sweeps down from the north, it meets up with warm, humid air pushing up from the south. While tornado formation is a very complicated process that scientists don't yet fully understand, this combination sets the basic requirements for frequent thunderstorms, lightning, hail, and tornadoes. Tornadoes are difficult to predict, and people often have little warning before a tornado strikes, which is probably why despite so many attempts to improve the amount of time of warning people receive, sadly during tornado season we seem to hear tragic circumstances associated with the fact that people had little or no warning.

What I personally have never really understood is the difference between a tornado "WATCH" and a "WARNING" and who makes the call on these, in other words who defines them and what is the warning process.