How are tornadoes rated using the EF-scale?

Canada adopted the Enhanced Fujita scale in April of 2013 after using the original Fujita scale for many years. Like the F-scale, the EF-scale uses observed damage to rate the intensity of a tornado and estimate associated wind speeds (Enhanced Fujita scale for wind damage).

The EF-scale however has improved relationships between observed damage and estimated wind speeds, and many damage indicators that list degrees of damage, from lightest to heaviest. The EF-scale adopted in Canada in 2013 is a slightly modified version of the original that was implemented in the United States in 2007.

The main differences are the addition or modification of a number of damage indicators (e.g., farm silos and grain bins - new, trees - modified). The minimum wind speed for EF0 was also lowered to 90 km/h in order to maintain consistency with ECCC warning criteria.

The EF-scale is used in two ways.

First, it is used to rate the intensity of damage to individual damage indicators along the damage path. This allows contouring of damage intensity, particularly useful for strong to violent tornadoes.

Second, the maximum intensity found along the entire damage path using the EF-scale is also used to characterize the strength of the tornado as a whole. EF/F0 and EF/F1 tornadoes are by far the most frequent in Canada (over 90%), though some of these might have been rated higher if more damage indicators had been present. This is particularly true for some parts of the Prairies.

The percentage of Canadian tornadoes that have been rated EF/F4 or higher is less than 0.5%. In fact, there has only been one recorded EF/F5 tornado in Canada, the Elie, MB tornado of 2007. Some NTP scientists are involved in the creation of a new and better version of the EF-scale that will eventually become a standard under the American Society of Civil Engineers for the first time.