The Enhanced Fujita Scale

Tornadoes are rated after the fact, based on the damage they leave behind:

• EF0 (105-137 km/h): branches broken, chimneys damaged
• EF1 (138-178 km/h): roofs peeled, mobile homes overturned
• EF2 (179-218 km/h): roofs torn off, large trees uprooted
• EF3 (219-266 km/h): whole stories destroyed, trains overturned
• EF4 (267-322 km/h): well-built homes leveled
• EF5 (over 322 km/h): near-total destruction

About 75 percent of tornadoes are EF0 or EF1 — brief and fairly weak. But the stronger 25 percent cause over 95 percent of all tornado deaths.