Environment Canada says the storm that ripped up electricity towers and damaged buildings in Lambton County on the weekend was an F2 tornado.
Officials said the tornado followed an 11 kilometer path southeast of Wyoming to Watford, Ont., channelling wind speeds of 180 to 230 km/h.
Environment Canada said witnesses reported a wall of white, which is consistent with a "rain wrapped tornado". These twisters are actually deadlier because it's hard to determine that they're actually tornados, it said.
Officials recommended that people not leave safety to chance, and head for shelter immediately if the wind picks up.