Alberta's Canada Day tornado given EF4 rating

A team of experts has classified a tornado that tore a path of destruction near Carstairs, Alta., on Canada Day an EF4.

The Northern Tornadoes Project (NTP), in collaboration with Environment and Climate Change Canada's (ECCC) Prairie and Arctic Storm Prediction Centre, made the determination Tuesday following an analysis of the damage left behind.

"The survey teams found that there was enough evidence to rate the tornado damage at EF4, with a maximum wind speed of 275 km/h," NTP said in a statement.

"The preliminary path length is 15.3 kilometres and maximum path width 620 metres."

Officials say 12 homes were impacted by the storm: three were destroyed, four were left uninhabitable and five others were damaged.

WHAT IS THE EF SCALE?

According to ECC, the EF (Enhanced Fujita) Scale is a six-point scale that ranges from zero (weakest) to five (strongest). It was adopted in April 2013 as "a more modern and improved version of the original Fujita Scale or F Scale.

"Environment Canada used the F-Scale to rate wind damage, in particular tornado damage, for several decades. However, the F-Scale, developed by Prof. T. Fujita in the 1960s, was found to have significant shortcomings. There was a limited number of damage indicators with which to rate damage, and engineering studies had shown that the F-Scale wind speeds were not well correlated with actual damage," ECCC said.

The new rating system takes into account a wider number of damage indicators, including homes, office towers and trees. It also "more accurately" records wind speeds by analyzing damage.

"The damage ratings are also backwards compatible with the original F-Scale; only the associated wind speeds have undergone major changes."

Table 1. Comparison of F-Scale and EF-Scale Wind Speeds

F/EF Rating	F-Scale Wind Speed Rounded to 10 km/h	EF-Scale Wind Speed Rounded to 5 km/h
0	60-110	90-130
1	120-170	135-175
2	180-240	180-220
3	250-320	225-265
4	330-410	270-310
5	420-510	315 or more

Table 1. Comparison of F-Scale and EF-Scale wind speeds (adapted for Environment Canada) associated with damage ratings. Note that for the EF-Scale wind speeds have been increased for lower ratings and decreased for higher ratings. (Source: ECCC)

When looking at the Canada Day tornado, experts found one of the homes destroyed was "well-built." That was factored into the storm's strength, which placed it into the range of wind speeds of 275 km/h.

Other damage at the property also illustrated how powerful the tornado was, the NTP said.

"In terms of nearby corroborating damage, various farm equipment was flipped and thrown at that property. This includes a combine weighing almost 10,000 kilograms that was thrown at least 50 metre, and then rolled for another 50-100 metres after that.

"Wind tunnel studies of another combine that was hit by a previous Canadian tornado suggest a wind speed of 230 km/h for just flipping a combine."

(Supplied/NTP)

STRONGEST SINCE 1987 TORNADO

Experts also said the tornado was one of only three F/EF4 tornadoes in Alberta and the strongest since the F4 tornado that struck near Edmonton 35 years ago.

That storm, on July 31, 1987, killed 27 people and injured more than 300. It also destroyed 300 homes.

The Canada Day tornado thankfully did not cause as much damage or injuries. The NTP says only one person, a first responder, received a minor injury.

The organization says there have been 21 "violent" tornadoes in Canada that have been classified as F/EF4 or higher. The country's only F5 tornado occurred in Elie, Man., in June 2007.

Further details, including additional photos of the scene, can be found online.