How damage determines a tornado’s EF rating

Severe Weather

GRAND RAPIDS, Mich. (WOOD) — Tornadoes can cause a wide range of damage as minimal as a few leaves shaken off trees or as serious as flattened buildings. Meteorologists use the Enhanced Fujita Scale, or the EF Scale, to rate how destructive a tornado was.

The local National Weather Service office will send a crew to the tornado path after a storm has passed to survey the damage. What they find allows the NWS to estimate the wind speeds produced by the tornado and eventually assign a rating based on those speeds.

The estimated wind speeds in a tornado path are different than measured, sustained wind speeds. We can measure wind speeds directly by using an anemometer on a weather station, but the odds of a tornado passing directly over a weather station (or the weather station escaping unscathed if that were to happen) are small. The EF Scale instead looks at a point of damage and estimates the three-second wind gust that would have caused damage of that degree.

The lowest rating that can be assigned is an EF-0, where the three-second gust is estimated at between 65 and 85 mph. Common damage found in an EF-0 tornado includes branches broken off softwood trees and roof panels ripped off barns.

Next is the EF-1 with estimated winds of 86 to 111 mph. Single-wide mobile homes can roll over under the force of the winds and softwood tree trunks can be snapped.

An EF-2 tornado has estimated winds of 111 to 135 mph. These winds are strong enough to destroy single-wide mobile homes and canopies on service stations can collapse.

EF-3 tornadoes are estimated to have wind speeds of 136 to 165 mph. Roofs can collapse over townhomes or apartments and entire warehouses can be destroyed.

The second highest rating that can be given to a tornado is an EF-4. The three-second gust is estimated at 166 to 200 mph. Isolated retail buildings and strip malls can be torn apart.

Finally, there’s the EF-5 rating, which is the most destructive rating that can be given to a tornado. Winds are estimated to be anywhere over 200 mph. The damage is incredible in a tornado of this caliber. Strong frame houses can be leveled, high-rise buildings can experience significant deformation and large shopping malls can be destroyed.

The ratings are not assigned until after the damage has been done. In addition to wind speends, keep mind that there are several more factors that influence how destructive a tornado may be. For example, an EF-2 passing over a town during the evening commute could be much costlier than an EF-5 briefly touching down in an empty field.

A tornado warning will be issued for any sort of tornadic threat, so all warnings should be taken seriously.

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