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Beginning Nov. 15, 2008, Quebec motorists will be required to install winter tires and keep them on until April 15 each year, under a provincial law passed Dec. 19, 2007. It is the first Canadian province to require the tires. (CBC)

In Depth

Forces of nature

Snow

A guide to the white stuff

Dec. 21, 2007

Sarah Donaldson tackles the snowdrifts Jan. 2, 2008, at her family's home in Moncton. (Photo submitted to CBCNews.ca by Cathy Donaldson)

It's just falling ice composed of crystals in complex hexagonal forms – a major part of Canadian life between November and early April. Unless, of course, you live in Victoria or Vancouver, where the mild Pacific is usually enough to ward off the white stuff.

So what is this substance that so consumes Canadians? Snow forms in clouds when water vapour turns directly to ice without going through the liquid stage.

We've developed quite the lexicon when it comes to the white stuff, but not quite the myth of the 400 words the Inuit allegedly have for snow. English or Inuktitut, there really are only a couple of dozen ways to describe snow – and the various ways it tests our patience.

Here's a quick guide to snow in Canada – and how to prepare for it:

While picking up your morning coffee at the local doughnut shop, you overhear the following conversation:

"I hear it's gonna snow today."

"Yup, we're getting some snow."

Here, the term snow is used without qualification. It means you can expect precipitation of significant duration and extent. Try to remember where you put your snow shovel.

Had the doughnut shop people said "we're expecting snow flurries or snow showers," you would have breathed a bit of a sigh of relief, because you knew that not much of the white stuff would accumulate. At least not enough to shovel.

You would have been even less concerned had they used the term snow grains – although very few of us do in normal conversation. Snow grains are very small snow crystals or the ice equivalent of drizzle. Not much to worry about – but you might have to scrape the windshield of your car a little.

One stage up is snow pellets, which are white, opaque particles that form as ice crystals fall through cloud droplets that are below freezing but still liquid. The cloud droplets freeze to the crystals forming a small lumpy mass – not the multi-pointed crystals of ice that make up snowflakes. Usually easy to shovel.

Among the nastiest stuff winter has to offer is sleet. This is formed when drops of rain or drizzle freeze into ice as they fall. Sometimes called ice pellets, these things sting when accompanied by a strong wind.

Even worse is freezing rain or drizzle. These water droplets maintain a temperature below 0 degrees C but do not turn to ice in the air. But they freeze as soon as they hit anything on the ground. Leads to much scraping of your car's windshield and slipping and sliding on sidewalks.

Ice crystals are tiny sprinkles that sparkle in the sunshine and hang in the air – usually when it's really, really cold out.

Snowstorms are a fact of life in Canada – and they can vary, depending on where you live.

Good old-fashioned blizzards, for instance, are rare in most of the country. The folks who watch the weather for a living define a blizzard as a severe storm that lasts three or more hours, and brings low temperatures, strong winds and poor visibility due to blowing snow. They're most common in the southern Prairies, Atlantic Canada and the Eastern Arctic, and are rare in the western Northwest Territories, British Columbia and the Yukon.

On Jan. 30, 1947, southern Saskatchewan was inundated with a series of blizzards that lasted 10 days. The storm blocked all highways in Regina and buried a train under a snowdrift that was one kilometre long and eight metres deep.

Diane Paquet clears snow in her driveway in Truro, N.S. on Monday, Jan. 24, 2005. (Andrew Vaughan/Canadian Press)

Thought that blowing snow and drifting snow were the same thing? There's an important distinction between the two. Blowing snow is lifted by the wind from the earth's surface to a height of two metres or more. Drifting snow is blown to a height of less than two metres. So if your head's poking out of a mound of snow and you're a little taller than two metres, it's drifting snow that got you.

Lake effect snow is most common near the Great Lakes. These squalls occur as cold air picks up substantial moisture as it moves over the lakes. The moisture gets dumped as snow inland from the downwind shore. Usually, they follow major storm systems that are cleared out of the area by blasts of Arctic air.

Often, the affected region will get a much bigger dump of snow from the squall than from the storm itself. In the more severe lake-effect snow squalls, accumulations of more than 75 cm per day are not uncommon, and fall rates as high as 28 cm per hour have been reported. Such severe snowfalls have been termed snowbursts.

These nasty little storms are often confined to small geographical areas. It could be snowing like crazy over your house – but bright and sunny (but really cold) a few kilometres away.

They may have some of the same characteristics, but there are some major differences between blizzards and snow squalls.

In a blizzard:

  • Winds must be sustained at 40 km/h.
  • Visibility is less than one km.
  • The wind chill value is greater than 1,600 watts per metre-squared, or the temperature is -25 C or lower.
  • The above conditions must be met for a minimum of four hours.
  • You do not have to have snow falling.

In a snow squall:

  • Snow must be falling.
  • A strong wind of at least 22 knots or 39 kilometres per hour must blow for at least one minute.

Yet another type of storm is sometimes called an Alberta clipper. This is a fast-moving winter storm that forms just east of the Rockies and sweeps south and eastward across southern Canada and the upper Midwest states. They're usually weaker than most winter storms and don't usually drop much snow. But they often bring along their evil twin – a surge of frigid Arctic air that can produce near-zero visibility in blowing and drifting snow.

There are various levels of warnings you will receive from your local weather forecaster. Pay attention, because there are significant differences between them.

If you hear a blizzard warning, expect snow or blowing snow, with a severe wind chill and visibility reduced to less than one kilometre, for four hours or more. Stock up on heating fuel and food. Stay indoors and wait out the storm – could be a long one.

A snow squall warning, however, means you might get hit by blizzard-like conditions over the course of the day. Or maybe the next town down the road will be. But be prepared for terrible driving conditions if you're in the path of a squall.

When you hear a heavy snowfall warning, you can expect 10 centimetres or more of snow to fall (15 cm or more in Ontario) in 12 hours or less. Travel could become hazardous, unless the plows get a good jump on the situation.

In Ontario, a winter storm warning is issued when two or more winter conditions reach warning proportions, such as wind and snow or freezing rain followed by heavy snowfall. You might want to think about hanging around the house for the day.

Winter storms and excessive cold claim more than 100 lives every year in Canada, more than the combined toll from hurricanes, tornadoes, flood, extreme heat and lightning. Many of those who die are killed trying to get rid of the stuff – stricken by heart attacks while shovelling snow off their driveways.

Some people may find freshly fallen snow very enjoyable to look at, but it can be pretty dangerous stuff. If you load a shovel with five kg of snow once every five seconds, you would move 60 kg of snow in one minute. Keep it up for 17 minutes and you will have shovelled one ton of snow.

Shovelling produces a rapid rise in heart rate and blood pressure – a combination that's tough on the heart. But cold can also act as a trigger for heart attacks, which is why some people suffer heart attacks while using snow blowers. Add to the mix that most people tend to ease off on the physical activity in the winter months, and you're looking for trouble if you try to crank it up after a big snow dump.

The Heart and Stroke Foundation of Canada offers these tips to avoid becoming a snow shovelling casualty:

  • Do take the time to do warm-up exercises to get your body accustomed to the vigorous exercise in the cold.
  • Do take frequent breaks so your body doesn't get too strained. The effort of picking up heavy show pushes up blood pressure more than aerobic exercise such as walking.
  • Do the shovelling as part of a group activity. Get the entire family out there to pitch in.
  • Do listen to your body. Stop shovelling if you experience any suspicious symptoms, such as sudden shortness of breath, discomfort in the chest, lightheadedness, nausea, dizziness or severe headache.
  • Do wear the appropriate clothing. You should layer clothing so you can remove the top layer if you get overheated.
  • Plan ahead. On days when heavy snowfalls are forecast, avoid rushing and allow adequate time for clearing the snow.
  • Don't continue shovelling just to get the driveway cleared in a hurry. If you're tired, quit.
  • Don't shovel or do any other vigorous activity directly after eating a meal. Your body is working hard enough just to digest the meal; adding vigorous activity on top of that could put too much strain on your heart.
  • Don't stoop to pick up the snow; bend at the knees to avoid back problems.

Go to the Top

MORE ON WINTER WEATHER

Environment Canada: Wind chill and the risk of frostbite

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