So far spring has been wetter than normal for most of the country; exceptions were in Southern Prairies and Alberta where normal precipitation was observed during the period.
Colder than normal conditions dominated across coastal BC, Alberta and the Prairies provinces at the beginning of the season, with a gradual come back to seasonal values in the Prairies and Alberta. Near to slightly above normal temperatures dominated across Ontario, Quebec and the Maritime provinces.
As the summer progresses, look for near normal temperatures in most BC regions. A strong blocking area of high pressure over Alaska will keep the polar jet stream riding to the north.
The jet stream pattern suggests cooler and wetter conditions for the north and central coast of BC. For the interior, generally dry conditions will favour an active summer season for forest fires.
On the lee side of the Rockies Mountains, most of Alberta will experience near normal temperatures, whereas the northern parts of the province will have above seasonal temperatures. Drier to near normal conditions will dominate the weather picture throughout the summer months.
Moving across the Prairies, we’ll see southern Saskatchewan and Manitoba tending to be slightly milder than normal. Expect below to near normal precipitation across the region.
Central portions of the country should continue to see mild temperatures. Expect above seasonal temperatures from northern into southern Ontario and Québec. The precipitation forecast is calling for higher than normal amounts from the lower Great Lakes region to the Maritimes.
Temperatures across the Maritime provinces and Newfoundland and Labrador will be near normal.
View Photo: 'Victoria Weekend Snowman!'posted by: rhonda, May 15, 2009, Yorkton, SK
What is La Niña
La Niña, meaning the little girl, names the appearance of cooler than normal waters in the eastern and central Pacific Ocean. Sometimes called El Viejo, anti-El Niño, or simply 'a cold event', it is the antithesis of El Niño.
La Niña is thought to occur due to increases in the strength of the normal patterns of trade wind circulation. Under normal conditions, these winds move westward, carrying warm surface water to Indonesia and Australia and allowing cooler water to up well along the South American coast. For reasons not yet fully understood, periodically these trade winds are strengthened, increasing the amount of cooler water toward the coast of South America and reducing water temperatures.
The increased amount of cooler water toward the coast of South America, causes increases in the deep cloud buildup towards southeast Asia, resulting in wetter than normal conditions over Indonesia during the northern hemisphere winter.
The changes in the tropical Pacific are accompanied by large modulations of the jet stream within the middle latitudes, shifting the point at which the stream normally crosses North America. The shifted jet stream contributes to large departures from the normal location and strength of storm paths. The overall changes in the atmosphere result in temperature and precipitation anomalies over North America which can persist for several months.
El Niño translates from the Spanish as 'the little boy' or 'the Christ child,' and is so called because the weak warm ocean current occurs along the western coast of South America around Christmas. El Niño is a very good example of the complex, intimate exchange between winds in the atmosphere and ocean currents.
In most years, strong, prevailing trade winds blow westward dragging the Earth's warmest surface waters across the Pacific to Australia and Indonesia. But every few years the trade winds slacken or change direction. Within a few weeks, the ocean responds to these changes. Without winds to hold it back, the warm waters to the west slosh back towards the coast of South America. This begins an El Niño. Some years the water warms up as much as 5 degrees C or more.
The atmosphere then responds to the rise in ocean temperature. The moist air above the warm waters also warms. It becomes buoyant enough to form clouds and tropical storms. The atmospheric stirrings cause heavy thunderstorms over the central Pacific, which in turn drive the jet streams that guide weather systems across the earth.
At one time, El Niño was thought to affect only South America's Pacific Coast, bringing flooding rains to Peru and ruining the anchovy fishery. Now we know El Niño can do very strange things to the world's weather for a year or even longer.
In some areas, El Niño means fairly predictable weather. For instance, it is almost sure to cause droughts in northeastern Brazil, eastern Australia and southern Africa, produce floods and mudslides in Ecuador, quiet the hurricane season in the Atlantic Ocean, delay the Indian monsoon, and bring copious winter rains to southern California.
In Canada, El Niño's impacts are considered marginal, showing up most clearly during wintertime in western Canada. But, El Niño is both good and bad news for Canadians. For example, in British Columbia schools of hungry mackerel riding the El Niño wave may devour young sockeye stock. For skiers, El Niño's usually snow-free winter is not welcome news. On the other hand, an El Niño year also correlates with a wetter spring and a warmer summer, making for good crop weather. When El Niño occurs, it seems to have something for everyone.