Environment Canada has issued a blizzard warning for parts of southern Ontario in advance of a massive storm that's set to dump up to 40 cm of snow on some areas on Wednesday.
It's the first time since March 1993 that such a widespread blizzard warning has been issued in the region.
The definition of a blizzard has recently changed.
Isabel Ruddick with Environment Canada said the organization began reviewing the criteria for what constitutes a blizzard in June 2010 and created a new official definition.
“The main idea was to harmonize the warnings and criteria across the country so that we would deliver a consistent warning program to Canadians,” she said in an email.
Environment Canada issues winter storm watches and warnings when 25 or more centimetres of snow are expected to fall within a 24-hour period or when snowfall is combined with other severe winter weather, including freezing rain, strong winds and extreme cold.
Blizzards are characterized mainly by strong winds -- specifically, winds that are expected to reduce visibility to 400 meters or less in combination with falling snow for at least four hours.
Environment Canada currently applies that criteria to storms anywhere in Canada south of the tree line. North of the tree line (the northernmost portion of the territories, northern Quebec and Labrador), the criteria is the same, but the conditions have to be expected to last for at least six hours.
Under the old definition, a storm would have to pack winds of 50 kilometers per hour or more, visibility of one kilometer or less, and windchill values of -25°C or lower to be considered a blizzard.
Chris Scott, a meteorologist with The Weather Network, says the new definition actually makes it easier for a storm to be classified as a blizzard.
“A couple of storms during 2008 could have been classified as blizzards with the new criteria.”
Eventually, even this definition of a blizzard will change.
Environment Canada is considering creating different alert levels related to the severity of conditions within the general definition of a blizzard.
For now, the current definitions of various types of severe weather can be found on Environment Canada's website.