Canada is a vast country, about 400,000 sq km/155,000 sq mi larger than China, situated between 42° and 83°N. A large part of Canada lies within the Arctic Circle, and only a narrow strip close to the southern border with the United States has a temperate climate. Much of this more favoured area has a severe winter with prolonged frost and snow. With the exception of Hudson Bay, which is frozen over for about nine months of the year, the northern coast of Canada on the Arctic Ocean is permanently ice-bound or severely obstructed for most of the year by ice floes. Only the Pacific coast of British Columbia and the Atlantic coasts of Newfoundland and the maritime provinces south of the Gulf of St Lawrence have harbours that do not regularly freeze in winter.
The reasons for the very cold winters over most of Canada are the high latitude of much of the country and the generally flat and low-lying land east of the Rocky Mountains. Cold air from the Canadian Arctic has virtually no obstruction as it sweeps south and east in winter and spring, thus importing very cold conditions to most of the country. Southern Canada also lies in one of the most frequented tracts of cyclonic depressions in North America; many of these cross the region of the Great Lakes and the St Lawrence valley before moving out into the Atlantic. The cold air involved in the circulation of these depressions frequently has its origin far to the north.
The influence of the warmer maritime air of Pacific Ocean origin is mainly confined to the small area of Canada west of the Rockies in British Columbia. The coast and some inland valleys in this province have a very different climate to the rest of the country, resembling that of the British Isles and other parts of northwest Europe. Here winters are mild and summers warm, with rain falling all through the year but with a maximum fall in winter.
Winter temperatures on the Atlantic shores of Canada are somewhat warmer than those in the interior of the continent, particularly where the sea does not freeze, but the summer temperatures are kept lower than in the interior because of the cold Labrador current, which flows southwards close to the coast.
Much of the interior of Canada has a very continental climate with surprisingly high summer temperatures, in spite of the shortness of the summer, and a long, very cold winter. Even the barren northlands of Canada have quite warm summers and in this there is a close parallel with much of Siberia.
For a more detailed description of the weather and climate of Canada it is most convenient to divide the country into the following climatic regions: eastern Canada, the St Lawrence and Great Lakes region, the Prairies, western Canada including the Rockies, and northern Canada.
Including (with towns and cities in parentheses) Newfoundland (St John's), the coast of Labrador, Nova Scotia (Halifax), New Brunswick (Fredericton), Prince Edward Island (Charlottetown).
This region includes those areas where the influence of the Atlantic Ocean modifies the harshness of winter to some extent and makes the summers rather more cool and changeable than farther inland. It has the most changeable weather around the year because of the large number of cyclonic depressions, which follow a track from the Great Lakes to Newfoundland. Frequent changes of weather from day to day are the rule in all months, and cloud and rain are well distributed around the year. Much of the winter precipitation is in the form of snow which, except on the coast, may lie for long periods. The tables for St John's and Halifax show the influence of the open sea in keeping winter temperatures a little higher and summer temperatures slightly lower than at places farther inland. The table for Chatham, which is only a little way inland from the Gulf of St Lawrence, shows how the annual range of temperature increases away from the sea.
This area is very liable to sea fog, and this can be persistent offshore during the summer months. The area above the Grand Banks of Newfoundland undersea feature in the North Atlantic and the Gulf of St Lawrence are among the foggiest sea areas in the world and lie across an important shipping route. Another navigational hazard in this sea area is the frequent occurrence of icebergs in summer; they drift south in the cold waters of the Labrador current. The temperature contrast between the warm waters of the Gulf Stream and the cold Labrador current is the principal cause of the fogs. This is one of the least sunny regions of Canada. Hours of sunshine a day range from two to three in winter to seven or eight in summer.
The St Lawrence and Great Lakes Region
Including (with towns and cities in parentheses) southern and central parts of Québec (Québec, Montréal), southern and central parts of Ontario (Ottawa, Toronto, Thunder Bay).
This region is bordered by the Great Lakes and the United States on the south and is the most southerly part of Canada. It is the most densely settled and developed part of the country. The southerly latitude and the warmth of the waters of the lakes, which do not usually freeze over completely until December, help to make this one of the warmest parts of Canada.
As the tables for Ottawa, Québec, and Toronto show, however, winters here are severe. Toronto, on the shore of Lake Ontario, has appreciably higher winter temperatures than Ottawa and Québec. Summers are quire warm with considerable amounts of sunshine, averaging eight to nine hours a day. Most of the winter precipitation is snow and the ground is usually snow-covered from mid-December to mid-March. This is one of the snowiest regions of North America, except for parts of the western Rockies. In an average winter 2.5-3 m/8-10 ft of snow may fall, but it does not necessarily accumulate to this depth because of periodic thaws and evaporation.
Like eastern Canada, the weather here can be very variable at all times of the year so that in some years there may be early or late cold spells and midwinter thaws. This variability of weather and the relatively high precipitation around the year are a consequence of this region's position in the track of numerous cyclonic storms.
The Canadian Prairies
Including (with towns and cities in parentheses) the southern and central parts of Manitoba (Winnipeg), Saskatchewan (Saskatoon, Regina), Alberta (Edmonton, Calgary).
This region lies between the western borders of Ontario and the Rocky Mountains. It is the most continental climate of any part of Canada. Winters are long and severe, with minimum temperatures not much higher than those recorded farther north in the Canadian Arctic. The relatively short summers are rather warm with a moderate rainfall, much of which falls in heavy showers. The summers are warm enough, and just long enough, to make this an important wheat-growing region. Like the Midwest region of the United States, which borders it on the south, it has much fine, sunny weather. Sunshine hours a day average three to four in winter and nine to ten in summer. Winter snowfall is comparatively light and the ground is often swept bare of snow by strong winds before the next fall occurs. The transition from summer to winter and from winter to summer often occurs very quickly, so that the concept of spring and autumn as understood in more temperate or maritime climates is misleading.
The tables for Winnipeg, Saskatoon and Edmonton are representative of this region. Calgary, however, tends to experience comparatively higher temperatures in the midwinter months of January and February due to the effect of the chinook wind, which can suddenly raise winter temperatures for a day or two at the foot of the Rockies. It is a föhn-type wind and occurs when air is drawn from the west across the mountains and is warmed as it descends on the eastern side. It can be very effective in melting snow quickly.
Canada west of the Prairies
Including (with towns and cities in parentheses) Alberta within the Rocky Mountains (Banff, Jasper), the southern and central parts of British Columbia (Vancouver, Victoria, Prince George, Prince Rupert).
This is a mountainous region with a very indented coastline on the Pacific Ocean. The highest mountains rise to between 3,000-4,000 m/10,000-13,000 ft and are found in two chains: the western or Coast Mountains and the eastern or main chain of the Rockies, and includes the Columbia Mountains. The area between consists of deep valleys and high plateaux. Because of this varied relief and wide range of altitude there are many local differences of weather and climate.
The Coast Mountains have a very heavy precipitation and above 1,200 m/4,000 ft much of this is snow. Some of the valleys have a very low annual precipitation; as little as 375 mm/15 in. The coastal region, which includes numerous islands, has a very mild winter climate with much rainfall at this season. It has the warmest winters of any part of Canada. Weather and climate around the year are very similar to that found in the British Isles, but the summers are a little warmer and sunnier. These mild winters quickly give way to severe conditions inland with frequent snowfalls in the mountains and quite low temperatures in the valleys where winter frosts are hard and frequent. This difference is well illustrated by the two tables for Vancouver, on the coast, and Prince George which is well inland in the valley of the Fraser River. The winter minimum temperatures at Prince George are almost as low as those experienced in the Prairies. The winter precipitation at Prince George is very much less than that on the coast.
This region is less sunny than much of central Canada. Winter sunshine is reduced by the more frequent cloudy days, and on the coast fog is a frequent occurrence. The summers are fairly sunny with an average eight to nine hours a day as compared with only two to three in winter. Although the weather is often changeable this is perhaps the most climatically favourable region of Canada; the coastal districts escape the harsh Canadian winter and the summers are warm and rarely too hot or oppressive.
Including (with towns and cities in parentheses) the Yukon Territory (Whitehorse, Dawson), the Northwest Territories (Norman Wells), Nunavut (Arctic Bay), the northern parts of British Columbia, Alberta, Saskatchewan, Manitoba (Churchill), Ontario, Québec.
This region comprises at least two-thirds of Canada but is very sparsely populated because it has such a harsh climate which is quite unsuitable for any form of agriculture. It resembles the climate of northern European Russia and Siberia. In the south it consists of a vast area of coniferous forest, to the north of which lies the Atlantic tundra region, covered with snow for eight to nine months of the year. In the far north the islands of the Arctic archipelago to the west of Greenland are covered with snow and ice throughout the year.
The harsh conditions during the long winter are well illustrated by the temperatures in the tables for Churchill, on the shores of Hudson Bay, for Norman Wells, on the Mackenzie River just south of the Arctic Circle, and for Arctic Bay, on the northern shore of Baffin Island. The tables show that at Churchill and Norman Wells temperatures can rise to quite high levels during the short summer. For much of the summer, however, the weather can be changeable and disturbed. Snow and frost may occur in any month when cold air is drawn down from the polar regions.
In the north of this region the phenomenon of permafrost is widespread. The top two or three feet of ground thaw during the summer but below this the earth is frozen for tens or even hundreds of feet. This poses particular problems for building and construction works which involve any foundations, whether housing, roads, or oil and gas pipelines. The line marking the approximate southern limit of permafrost runs from northwest to southeast from the Yukon and Great Slave Lake to the southern shore of Hudson Bay and then eastwards to the coast of Labrador.
Wind chill is a frequent, and probably the most dangerous, weather hazard in northern Canada. During severe weather in winter it can be a serious problem in almost any part of the country, except on the west coast. A combination of low temperature and high wind is much more dangerous than very low temperatures in still air or a very light wind.
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