La Niņa conditions continued across the Pacific Basin during January, where Sea surface temperatures indices remained below average. Low-level easterly winds and upper-level westerly winds also continued across the equatorial Pacific Ocean. These oceanic and atmospheric conditions reflect La Niņa.
During La Niņa, impacts on the weather are less predictable than the effects wrought by El Niņo. This is mainly because of the big differences in the jet stream and the storm track. El Niņo causes the Pacific storm track to become stronger, to drop farther south than usual, and to straighten out like a necklace of weather extending more-or-less straight across the ocean. The La Niņa storm track is weaker and loopy and irregular, like a piece of wet and wiggly spaghetti, more changeable, so the behavior and direction of the storms it carries are more difficult to accurately forecast. Models forecast generally indicate a gradual weakening of la Nina through an eventual transition to neutral conditions by the end of the Spring 2009.
As the season progresses, look for the west coast to be slightly cooler than normal on average as the jet stream will tend to ride lower as water temperatures in the eastern Pacific affect the flow. This should also keep most of the weather systems passing across the BC Interior. Areas in the southern and central interior of BC will experience wetter than normal through to May.
As we move into the Prairies, we see the southern tiers of Manitoba tending to be slightly milder and wetter than normal. This should be one of the main tracks for the developing Spring storms across southern Manitoba and Northwest Ontario, leading to wetter than normal conditions. As systems move through, look for large temperature shifts from the mildly warm to a distinctly wintery chill.
The Central and Eastern portions of the country should continue to see wild temperature swings through mid April, ending the season with average near normal temperatures. Precipitation patterns across most of eastern Canada will be near normal, but look for some heavy rainfall across southern Ontario in late April and a few more snowy events across the Maritimes through mid March as the weather patterns fluctuate.
Issued: February 18, 2009