Tornado in southwestern Manitoba gets 'high-end EF-2' rating

A violent tornado thatroared throughsouthwestern Manitoba earlier this week has received a "high-end EF-2" rating from Environment Canada.

The preliminary rating was issued late Wednesday afternoon, following an assessment by meteorologists who surveyed the damage between Pierson and Virden, Man., following Monday night's twister.

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A tornado ratedEF-2on theEnhanced Fujita Scalecomes with wind speeds of 179 to 218 km/h and leads to roofs blown off homes, sheds destroyed and mobile homes flipped.

Environment Canada has called Monday's tornado a "rare" event, as radar imagery shows it stayed on the ground for 2 to three hours. In Canada, tornadoes rarely stay on the ground longer than a few minutes.

Earlier, Environment Canada meteorologistNatalie Hasell saidthe team was lookingat damage to buildings to help rate the twister. But any quick clean up by people in the area could presenta challenge, she said.

"If it goes through a field, there's not a whole lot to rate there.But if it touched buildings that typeof indicator can give us an idea how sturdy the structure was and then we can rate the damage," Hasell said.

"Once the damage is rated then we get the EF,that enhanced fujita scale rating."

Environment Canada says it's still surveying the area. It's asking people who may have taken photos of the tornado or the damage to call 1-800-239-0484 oremailstorm@ec.gc.ca.

How do we rate tornadoes?

On April 1, 2013, Environment Canada adopted the Enhanced Fujita Scale or EF-Scaleto measure the strength of a tornado (it had been in use in the U.S. since February 2007). It'san improved version of the original Fujita Scale that wasdevised in 1971 by a pioneer in tornado research at the University of Chicago, Tetsuya (Ted) Fujita.

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The new EF-Scaleestimates three-second-gust wind speed inside a tornado based on the damage that's observed by examininga large number of indicators, ranging from residential housing to office towers to trees, as well as ground markings and meteorological data. The EF-Scale damage ratings are backwards-compatible with the original F-Scale, butthe associated wind speeds have undergone major changes.

The EF-Scale ranges from 0, for a tornado that pushes over shallow-rooted trees and causes some damage to chimneys and signs, to 5, when houses are lifted off their foundations, vehicles are thrown 100 metres or more, and trees are uprooted and carried long distances.