Significant Weather Events in Niagara

Weather definitions

Local snow accumulations may be significant.

• Blizzard

  When winds of 40 km/hr 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.

• Blowing snow

  When blowing snow, caused by winds of at least 30 km/hr, is expected to reduce visibility to 800 metres or less for at least three hours.

• Snow fall

  When 15 cm or more of snow falls within 12 hours or less.

• Snow squall

  When, down wind of large bodies of water, like the Great Lakes, snow squalls are imminent or occurring with one or more of the following conditions being produced:

  • Localized, intense snowfall producing snowfall amounts of 15 cm or more in 12 hours or less
  • Reduced visibility (less than 400 metres) caused by heavy snow with or without blowing snow for three hours or more
• Flash freeze

  When significant ice is expected to form on roads, sidewalks, or other surfaces over much of a region because of the freezing of residual water from either melted snow, or falling / fallen rain due to a rapid drop in temperature.

• Freezing rain

  When freezing rain is expected to pose a hazard to transportation or property or when freezing rain is expected for at least two hours.

• Freezing drizzle

  When a period of freezing drizzle is expected for at least eight hours.

• Winter storm

  When severe and potentially dangerous winter weather conditions are expected, including:

  • A major snowfall (25 cm or more within a 24 hour period)
  • A significant snowfall (snowfall warning criteria amounts) combined with other cold weather precipitation types such as: freezing rain, strong winds, blowing snow and / or extreme cold
  • Blizzard conditions may be part of an intense winter storm, in which case a blizzard warning is issued instead of a winter storm warning