The Enhanced Fujita scale, explained

The ratings

The scale ties damage to estimated three-second gust speeds. The ranges below are the standard estimates published by the National Weather Service.

• EF0: 65 to 85 mph: light damage, such as broken branches and peeled shingles
• EF1: 86 to 110 mph: moderate damage, such as stripped roofs and overturned mobile homes
• EF2: 111 to 135 mph: considerable damage, such as roofs torn off houses and large trees snapped
• EF3: 136 to 165 mph: severe damage, such as entire stories of houses destroyed
• EF4: 166 to 200 mph: devastating damage, such as well-built houses leveled
• EF5: over 200 mph: incredible damage, such as strong frame houses swept from their foundations

Rated by damage, not by looking at the funnel

A tornado cannot be rated while it is happening. Survey teams from the National Weather Service examine the damage afterwards, comparing it with a list of damage indicators (different kinds of buildings and structures — and judging how severe the damage is for each. The highest damage found sets the rating.

That means a violent tornado that crosses open fields can be rated low, because there was little to damage. The rating describes what the tornado did, not the most it could have done.

Size is not strength

A wide tornado is not automatically a strong one, and a narrow one is not automatically weak. Width, wind speed and path length are all separate measurements. Wedge tornadoes tend to be wide and are often, though not always, intense.

Why the scale was changed from Fujita

The original Fujita scale, from the early 1970s, had little guidance on how damage related to wind speed. The EF scale added damage indicators and refined wind estimates so that ratings are more consistent from one survey to the next.