Why La Nina Has Brought Fickle Winter Weather

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Unless you’re in Japan or St. Anton right now, you’ve probably noticed there isn’t a lot of snow. From Squaw Valley’s 12-inch base to Mad River Glen’s 40 inches all season, skiing in North America is looking bleak. Sadly, this snowless winter is coming in a La Nina year, which typically produce whiter forecasts.“Last year was a strong La Nina year, and this is a weak to moderate La Nina year,” said Greg West, a postdoctoral fellow with the University of British Columbia’s Weather Forecast Research Team, and the founder of Utahskiweather.com. “I think the important lesson from this year is that La Nina increases the chances of a colder, wetter year, but doesn’t guarantee it.”Some ski areas, like Vermont’s Magic Mountain, aren’t even open, while most resorts have limited terrain available. Weather Underground meteorologist Kari Kiefer said the scant snowfall throughout the West is the result of a dominant ridge of high pressure that has hovered over the West Coast for a month. “This ridge is strong enough to shove any other systems northward that move in from the Pacific Ocean,” said Kiefer. “This is why British Columbia and the Pacific Northwest have seen snow, but not the Sierras.” This Dec. 2011 photo shows the Lake Tahoe area. Although La Nina brought a lot of snow last season, there has been less snow this season — a lot less. Mountain communities across America are hoping for more snow. Kiefer said that some systems that track through the Northwest and BC slide back down the northern and central Rockies, which is why Colorado and Wyoming have received snowfall. Unfortunately, Kiefer said the weather models predict the weak to moderate La Nina to persist through February and March.West was more optimistic. He said that the arctic oscillation index, a term in meteorology to measure the differences in pressure between northern latitudes and mid latitudes, have been positive this year, which means arctic air is bottled up rather than moving down to the continental US. (In fact, the past two winters have recorded AO values that have been the highest and lowest ever recorded, indicating strongly anomalous weather.) But West said the forecast is calling for the oscillations to go negative, at least temporarily, in the next week. That could lead to more snowfall.“There’s still a lot of winter left, and it could change,” said West.

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