Article contentWhen Environment Canada issues severe weather or tornado warnings, data to support those warnings is provided by Instant Weather, a partner of the Northern Tornado Project at the University of Western Ontario. Environment Canada’s website says a tornado watch is issued when conditions are favourable for the development of severe thunderstorms with one or more tornadoes. Warnings are issued when a tornado has been reported, or when there is evidence based on radar from a reliable spotter that a tornado is imminent.