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Mild start to winter puzzles Canadians


Where's winter?
Where's winter?

Alexandra Pope, staff writer

January 8, 2012 — A climatic phenomenon called the North Atlantic Oscillation Index can help explain why parts of Canada have been so mild lately.

Below-average snow season in the west
Below-average snow season in the west

If you asked Canadians to rate how wintery it's been in their area lately, many would say 'not at all.'

British Columbia, the Prairies and Atlantic Canada have all seen periods of record-breaking mild weather since the beginning of December.

Snowfall totals have also been well below average right across the country.

Vancouver, which normally sees 23 cm between the start of their snowy season and now, has only seen one centimetre so far.

Edmonton and Calgary have done slightly better. Edmonton has seen close to 50 per cent of its average September to February snowfall with 35 cm so far, while Calgary has seen 39 cm -- about 60 per cent of its average for the same period.

In Toronto, the snow has virtually been a no-show. Only 9 cm has fallen at Pearson International Airport since the end of November, and none of it has stuck around into the new year.

Totals are also way down in parts of Atlantic Canada. Moncton, which weathered an exceptionally snowy season last winter, has only seen 55 cm so far this season -- well below the end-of-January average.

St. John's, Newfoundland can boast 82 cm, but that's also well below their average of 170 cm.

Mild and melting in Saskatchewan. Even the birds are confused
Mild and melting in Saskatchewan. Even the birds are confused

The springlike weather may seem surprising given that meteorologists had been calling for a winter similar to last year's.

Weather Network meteorologist Rob Davis says one explanation is the North Atlantic Oscillation (NAO) Index.

The NAO is the natural fluctuation of air pressure in the northern Atlantic Ocean, which influences the movement of storm systems across the continent.

“For the last couple of years, we've had a negative oscillation, which favours cold outbreaks and snowy systems,” Davis explains. “This year, we have a positive oscillation, which sees more Pacific air pushing into the Prairies, keeping cold air locked in the Arctic.”

That means fewer extreme cold outbreaks for the Prairies and fewer Colorado and Texas lows bringing snow to central and eastern Canada.

However, unlike the El Niño and La Niña phenomena in the Pacific Ocean, which change and persist over periods of months or years, the NAO can change in a matter of weeks and is less predictable, Davis says.

The U.S. National Oceanic and Atmospheric Administration says La Niña is still a factor in the Pacific Ocean, so Canadians shouldn't write off winter just yet.

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