Snowy winter ahead? Forecast still cloudy

Winter hasn't even started, but evidently it's already befuddling the forecasters.

The early consensus among the seasonal outlooks was that December would get off to a brisk, wintry start in the East.

But evidently that's out the window.

On Thursday, Accu-Weather Inc. plans to update its winter outlook, and it's likely to go warmer for December. The Commodity Weather Group in Washington already has added a few degrees to its December forecast for the East.

With a degree of certainty, climate experts have been saying the world will keep getting warmer for at least another century. Notable glitches notwithstanding, short-range and seven-day forecasts have improved measurably in the last decade.

So why can't meteorologists tell us just how much snow we're going to get and how cold it's going to be for the next three months?

It's not for lack of trying. Never have more meteorologists been involved in long-range forecasting, and they've had some successes. Never has the speculation been more fascinating and detailed.

But seasonal forecasting remains one of the most elusive pursuits in meteorology.

"I don't see it solved in the next 10 years," said Mike Halpert. "Maybe ever." And this is what he does for a living as deputy director of the government Climate Prediction Center outside Washington.

In his view, making a detailed forecast for a three-month period is "all but impossible." Maybe not for Death Valley, but definitely for Philadelphia.

What's the problem?

Short-term forecasts rely on computer models that take the "initial" state of the atmosphere, derived from observations all over the world at a given time. They then compare those states with previous ones and try to figure out how they will change in the coming hours and days.

However, the observations aren't perfect, and the world is full of data holes. The small errors cascade, and over time the forecasts become less and less reliable. They aren't much good beyond seven to 10 days.

Long-range forecasters look at "teleconnections," how what happens in one neighborhood of the atmosphere may affect another over the next several weeks.

The most useful is the well-known El Niño-La Niña cycle. Every few years, a continent-size patch of the tropical Pacific becomes unusually warm - El Niño - or cool, La Niña.

Right now, a weak La Niña has taken hold. Typically, that would mean cool in the Northwest and warm and dry in the Southeast. But for a huge section of the country that includes Philadelphia, Halpert said, the Niña signal isn't much help.

Judah Cohen, a scientist at AER Inc. in Massachusetts, says he has identified a promising connection between October snow cover in Siberia and the U.S. winter. Going against the consensus, he correctly called for cold in the East last winter. (He sees no clear-cut indicator for this winter, however.)

"Obviously, it's something to look at," Halpert said.

But he added that in the Northeast United States, as well as in Western Europe, winter is heavily dependent on an atmospheric pattern known as the North Atlantic Oscillation.

It is tracked by an index of air pressure - the weight of the atmosphere - at stations near Greenland and Portugal. When it's higher in Greenland, cold pours into the northeastern United States, and the reverse is true when the pressure is higher near Portugal.

Unfortunately, the oscillation isn't predictable beyond about two weeks, he said. And that remains a major issue for seasonal outlooks.

For now, Halpert advises savoring the mysteries of the atmosphere.

"People want to know, and you can't know everything," he said. "So be surprised."