The upgrade of a winter storm warning to a blizzard warning sparked questions on social media sites like Twitter about the difference between the two alerts. To help clarify, here are the thresholds for each as defined by Environment Canada.
A blizzard warning is declared when winds of 40 kilometres per hour or greater are expected to cause widespread reductions in visibility to 400 metres or less due to blowing snow, or blowing snow in combination with falling snow, for at least four hours.
A snowfall warning in Alberta is declared when 10 centimetres of more of snow falls within 12 hours or less.
A winter storm warning is declared when severe and potentially dangerous winter weather conditions are expected, including
A major snowfall (25 centimetres or more within a 24 hour period); and
A significant snowfall (amounts meeting the criteria for a snowfall warning) combined with other cold weather precipitation such as freezing rain, strong winds, blowing snow and/or extreme wind chill.
Blizzard conditions may be part of an intense winter storm, in which case a blizzard warning is issued instead of a winter storm warning.
Source: Environment Canada