Fujita Scale

F 0
the weakest tornadoes
maximum wind speeds are close to 70 mph
some tree damage, shingles removed from homes, and windows cracked

F 1
still a fairly “weak” tornado
maximum wind speeds are close to 110 mph
trees broken at the trunk, windows broken

F 2
this is considered a “strong” tornado
maximum wind speeds are close to 150 mph
trees uprooted, trailer homes destroyed

F 3
this is also considered a “strong” tornado
maximum wind speeds are close to 200 mph
cars overturned, roofs and walls destroyed

F 4
maximum wind speeds are close to 260 mph
homes removed from their foundations, cars may be carried a short distance

F 5
these are the strongest of tornadoes and the strongest winds on Earth
wind speeds inside an F 5 are greater than 260 mph
damage is extreme -- cars carried ¼ mile or more, homes completely destroyed, concrete removed from roadways

Tornado Watches and Warnings
Tornado Watch:
This is similar to a Severe Thunderstorm Watch. The Storm Prediction Center in Norman, Oklahoma will issue this watch when conditions are favorable for tornadoes. Conditions will be similar to Severe Thunderstorm Watch criteria at the surface and the winds will usually be from different directions at different altitudes. For example, the surface wind may be from the south while the wind at 30,000 feet is from the west. This shifting of winds with altitude can help create a tornado’s rotation. These watches usually cover very large areas, just like severe thunderstorm watches.

Tornado Warning:
Storm spotters and Doppler radar are used to find tornadic thunderstorms. Trained storm spotters are dispatched across the area when conditions are favorable for tornado development. These spotters have the responsibility of contacting the closest National Weather Service office and reporting tornado sightings. A tornado warning means that a tornado has either been spotted or indicated by radar. Just like severe thunderstorm warnings, tornado warnings are only issued for one or two counties at a time. If you are in the warned area, you should seek indoor or underground shelter immediately.