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Don’t like cold? El Nino’s your friend

Posted: Wednesday, October 25, 2006

It’s going to be a long, dark and warm winter.

That’s right — warm. Oh, there’ll be considerable cold, of course, along with howling winds to shiver your bones and drifts deep enough to keep the snow blower busy.

But by typical winter standards, there’s a fair chance the chill factor will be moderate. And after this year’s wet and chilly summer, something as out of whack for Alaska as a warm winter seems somehow fitting.

According to a three-month, long-range forecast map for October, November and December found on the National Weather Service’s Climate Prediction Center Web site, the Kenai Peninsula and much of Southcentral Alaska will be in the weather service’s “equal chance” zone, meaning its temperatures will be equally likely to be either above or below normal.

The situation changes for the peninsula and Southcentral come 2007, however. The map for January, February and March shows above-normal temperatures spreading across Alaska from Juneau to Kachemak Bay and then north to Barrow, leaving only Western Alaska in the “equal chance” zone.

For Southcentral Alaska and on out to Bristol Bay, the above-normal trend continues through April, May and June 2007, while a band from Juneau to Fairbanks to Nome should dwell in “equal chance” weather patterns.

Thus, for much of the late fall and through the winter, folks on the Kenai Peninsula should see generally warmer temperatures — for winter, that is.

Why?

El Nino in the southern Pacific Ocean is likely to blame, along with a general warming trend in Alaska that has been going on at least 20 years, said Bob Hopkins, meteorologist in charge with the National Weather Service’s Weather Forecast Office in Anchorage.

Hopkins cautions, however, that predicting above-normal temperatures amounts to relying on probabilities, not absolutes. That is, when above-normal temperatures are predicted, that really means there’s about a 55 percent chance they’ll actually occur. That also means there’s a 45 percent chance they won’t.

“That’s about the state of the science,” Hopkins said.

Such predictions can prove useful to, say, industries, and may allow them to make better economic plans.

“That’s one of the reasons we do it,” Hopkins said.

One of the better indicators of warmer Alaska weather is the presence of an El Nino, a condition defined by an eastward flow of warmer water from the western Pacific that elevates air temperatures off the coast of South America. This can send warmer water and air northward along the entire West Coast of the Americas.

A ridge of high pressure can build up in the atmosphere along the coast of North America, turning the jet stream north across our part of Alaska (rather than into British Columbia) and producing a warming effect, Hopkins said.

An El Nino is currently under way and can be expected to last for months. About seven out of every 10 El Nino events produce warmer temperatures in Alaska, Hopkins said. Of course, three out of every 10 times it occurs temperatures might be cooler.

Still, “That’s great odds when it comes to forecasting,” Hopkins said.

The weather service looks at monthly average temperatures when trying to make long-range predictions. Historically, almost all broad variations year to year happen during the winter months. Summers are typically much less radical. “This was not a bad summer,” Hopkins said, adding that the previous two have been unusual.

If this winter’s temperatures prove to be above normal, Southcentral might see a lot of snow. Average warmer weather doesn’t necessarily equate to rain, he said.

Global warming likely is contributing to the generally higher temperatures. Hopkins said climatologists use a standard process that computes “normals” over a 30-year period to produce a running average.

“Every 10 years , we kick in the next decade,” he said. “Our normals in Alaska have been going up over the past 20 years.”

Still, there are many more factors contributing to the weather patterns, Hopkins cautioned.

“It’s very complex,” he said.

Bottom line: Southcentral and the Kenai Peninsula stand a better than 50/50 chance of seeing warmer-than-usual temperatures during the coming winter, and that may translate into significant snowfall.

On the other hand Well, you get the idea.

Hal Spence can be reached at harold.spence@peninsulaclarion.com.



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