The Fujita Scale is a rating of numbers that tell how violent the tornado is. The ratings go from F0 to F6. The worst rating is F6. They usually won't worry about the tornadoes that are rated F2 and below.

F-0= Gale tornado, 40-72 miles per hour

F-1= Moderate tornado, 73-112 miles per hour

F-2= Significant tornado, 113-157 miles per hour

F-3= Severe tornado, 158-205 miles per hour

F-4= Devastating tornado, 206-260 miles per hour

F-5= Incredible tornado, 261-318 miles per hour

F-6= Inconceivable tornado, 319-above miles per hour