|Posted by Jeff on October 30, 2010 at 3:45 PM|
An intense hit of 'La Nina' will mean a big shift in temperatures halfway through the season.
The return of the La Nina effect means winter across Canada this year will not be a repeat of last year's balmy temperatures in many parts of the country, instead changing to a much colder, traditional one.
"The first half of winter will probably not be as winter-like, compared to the second half, where La Nina will kick in and be more of a dominant force," says Environment Canada weather guru David Phillips.
La Nina is the evil twin sister of El Nino, a cooling of the ocean in the central and eastern Pacific region that heralds colder weather for North America. El Nino has the opposite effect, which triggered last year's balmy winter
Scientists are predicting a moderate to intense La Nina this winter. But before you race down to Canadian Tire for another snow shovel, Phillips points out the winter's predicted coldness, if it materializes at all because such long-range forecasts aren't ironclad, is relative.
With global warming or perhaps cyclic weather trends, winter ain't what it used to be, he says.
"Anything that is even normal this year will seem more brutal, more difficult, than last year," says Phillips.
A look at the weather office's seasonal forecasts show Western Canada will bearing the brunt of La Nina's effect once winter really sets in.
"You see most of the West being colder than normal," says Phillips. "But from a little bit of the southern prairie through most of southern Ontario and Atlantic Canada we're showing conditions to be a little bit warmer than normal.
"So the full effects of La Nina may not necessarily get to the East."
But other factors, whether it's long-term weather cycles or climate change, could mitigate the bad girl's effects.
"It's a huge country and the signal can be very different on the west coast than it is on the east coast," he says.
Unlike El Nino, with its tropical vibe, La Nina can be capricious. It doesn't create weather extremes like ice storms or mega snow dumps. But expect frequent changes through the winter, says Phillips, "two weeks of this and two weeks of that . . . more surprises, something for everybody."
British Columbia will bear the brunt of a La Nina winter, colder and weather than normal, while the Prairies will see a late start and face the toughest part of winter from January on, especially in the north.
Phillips says Central Canada should expect warmer than normal temperatures, more snow and storms, "but not the ice age cometh," says Phillips. La Nina may not reach that far but he points out Ontario and Quebec enjoyed El Nino's full effects last winter.
Predicting Atlantic Canada's winter is tougher in part because north Atlantic waters are two to three degrees warmer than normal, which could delay things. But the region is vulnerable to the threat of consecutive dumps of snow.
If scientific forecast models generated by super computers aren't your thing, check out this guide to predicting winter from the Waterman and Hill Traveller's Companion Natural Event Guide.