Fall and winter weather hazards

Winter is a naturally hazardous season in Canada because of its extremely cold temperatures, challenging driving conditions and severe winter storms.

You should be careful when severe winter weather strikes or when travelling in potentially hazardous winter environments. Such environments include frozen bodies of water and avalanche zones.

Avalanche safety

Climate and historical weather

Blizzard

A blizzard occurs when strong winds and heavy or blowing snow combine to cause low visibility. In whiteout conditions created by blizzards, people have become lost even when going only short distances. In Canada, the region that experiences the most hours of blizzard conditions extends from Resolute, Nunavut to Churchill, Manitoba.

Freezing rain and ice pellets

Freezing rain or freezing drizzle is precipitation that falls in liquid form at first, but then falls through a layer of cold air. If this cold air layer is thick enough and the air temperature is below freezing, the precipitation freezes on contact with objects on the ground that are below freezing temperature, forming a coating of ice on its surface.

Driving and even walking can be dangerous in such conditions. Ice-coated utility lines or poles can fall down due to the excess weight of the ice.

Ice pellets are raindrops that freeze before they reach the ground, after falling through a layer of air that is below freezing.

Ice fog

Unlike regular fog, which reduces visibility due to suspended water droplets, ice fog reduces visibility due to suspended ice crystals. Ice fog occurs at very cold temperatures and is rare at temperatures warmer than -30o C. Ice fog can form very quickly in the right conditions and has been known to develop immediately after a plane’s take-off.

Driving any vehicle in low visibilities due to ice fog can be hazardous and speeds should be reduced accordingly.

Rain

Rain in the winter can have serious impacts when it falls on a snowpack or on frozen ground, as the increased runoff can lead to flooding. When heavy rainfall is expected that could contribute to localized or downstream flooding and other hazardous conditions, Environment and Climate Change Canada issues a rainfall warning. For some areas of the country, the criteria used for issuing a rainfall warning in the winter is lower than that for a summer rainfall warning.

Snow

Although it can snow anywhere in Canada during the winter, the amount of snowfall varies greatly from region to region. It snows less in the North and the interior plains because the air is very dry. Along the west coast of the country, precipitation falls more often as rain, because of the warming effect of the Pacific Ocean. Moving inland, snowfall increases to its maximum in the Rocky Mountains. Similar amounts are reported in the Gulf of St. Lawrence due to frequent winter storms. Further inland, the winter accumulations of snow drop due to a lack of moisture. Heavy snowfall can greatly reduce visibility, create hazardous road conditions, and knock down trees and power lines.

Criteria for public weather alerts: snowfall

Blowing snow is snow driven by strong winds. It reduces visibility and can cause deep drifts, which can impede transportation and make driving dangerous. Snowdrifts and snow plow deposit can also make it difficult for people to leave their homes or get out of their driveways.

A snow squall is a sudden, moderately heavy snowfall with blowing snow and strong, gusty winds that reduce visibility. Intense but very localized, snow squalls usually last for a relatively short period of time. They often blow in off the Great Lakes, the Gulf of St. Lawrence, and other large bodies of water.

Wind chill and cold temperatures

Wind chill is when the wind makes cold temperatures feel even colder. Environment and Climate Change Canada’s wind chill index will tell you the combined cooling effect of these factors on the human body. It uses temperature-like units to liken the current conditions to how cold your skin would feel on a calm day. Cold temperatures can also be hazardous, even if there is little or no wind.

Wind chill and cold temperatures can cause exposed skin to freeze very quickly, leading to frostbite. Extremely cold conditions can cause hypothermia, a potentially fatal condition. Protect yourself by taking steps to stay warm when you are outdoors.

Canada’s wind chill index

Smog

Smog is not just a summertime concern. It can also occur in the winter, often in communities where wood is used for home heating. Winter smog is made of fine airborne particles, mainly from wood smoke, traffic and road salt. These pollutants can build up in the local area during cold weather, when there is little wind to disperse the particles. This often occurs during temperature inversions and in valleys and other areas that are sheltered from the wind.

Winter smog can be a health hazard, as fine particles can be inhaled deeply into the lungs. Children, the elderly, and people with heart or lung conditions are most at risk. When winter smog occurs in your community, you can help clean the air by not burning wood in your fireplace or woodstove, and by reducing the use of your car.

Environment and Climate Change Canada’s Air Quality Health Index helps to track winter smog in your community and find health information. Use our daily forecasts to plan ahead to protect your health and that of your family.

Winter smog

Air Quality Health Index

Winter storm

Winter storms are large-scale weather systems that measure hundreds of kilometres across. They are called extratropical cyclones because they form and develop outside of the tropics. These storms gather their energy from the temperature and moisture differences across the boundary where different air masses come together. The larger the differences in the temperature and moisture levels across this boundary, called a front, the more energy there is available for the storms to develop. This is why some are stronger or more intense than others.

Winter storms tend to move from west to east and can produce strong winds, heavy snowfall, freezing rain and bitterly cold temperatures as they affect a given area.

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