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On Philadelphia’s chilliest days in seven months, U.S. releases winter outlook

With the atmosphere about to nudge the calendar forward a month, the feds say odds favor a mild winter in most of the country — but not necessarily around here.

Plowing a Colorado driveway on Monday after a pre-season snowfall. Almost 'tis the season.
Plowing a Colorado driveway on Monday after a pre-season snowfall. Almost 'tis the season.Read moreHelen H. Richardson/The Denver Post via AP)

While the atmosphere might be behaving as though it's Thanksgiving around here, meteorologists have jumped ahead to Christmas, New Year's Day, and beyond.

The government this week joined the annual quixotic exercise to wrestle with the atmosphere's often inscrutable ways and address the question: What's the winter going to be like?

The answer for the Philadelphia region was predictably uncertain: Signals are mixed on temperatures, but chances are good that precipitation will be above normal along the southeast and mid-Atlantic coasts, suggesting an active storm track.

But, no, the climate center did not get take on  the how much for Philly? question. In a briefing Thursday — the coolest day in Philadelphia in seven months — forecaster Mike Halpert cautioned that the center isn't in the snow-forecast business just yet and that the outlook is "probabilistic in nature."

The outlook is far less specific and more muted than the ones issued by private-sector companies, one of which sees pre-winter patterns similar to those of 1995-96 and 2009-10. Those happen to be the two snowiest winters on record around here.

Talk of winter might have a particular bite given the chill that routed the summery spell earlier in the month. Temperatures rose into the 80s on six of the first 11 days of October. But they dropped to freezing and below on Friday morning outside the city, and Sunday's 50-ish forecast would be normal for the end of November. Readings are due to stay below averages at least through Thursday.

However, the chill isn't necessarily a harbinger.

The forecasts assembled at the Climate Prediction Center are objective and "probabilistic" because they are constrained by the unforgiving limits of a science that has long shown promise but has been consistently outwitted by the atmosphere.

Last winter, for example, none of the early outlooks caught wind of the record-shattering warm February in the Mid-Atlantic and Northeastern United States.

The computer models that have had such amazing success (OK, not always) in short-term weather prediction haven't produced the same results in the long range.

Short-term computer models suffer from incomplete observations of the present state of the atmosphere — think of the oceans, and less-developed nations that have bigger issues than figuring out the temperature — and the forecast errors worsen over time.

Halpert said computer advances would be the key to progress in long-term forecasting. But for now, one of the most-useful tools is the "optimal climate normal," a fancy phrase for "overall trend."

Most recent winters have been mild in the U.S. Asked whether that was a function of worldwide warming and whether the trend would continue, Halpert, hedging his bets, answered, "I'm probably not going to touch the 'continue.' "

The atmosphere is what scientists call a nonlinear chaotic system. It is three-dimensional and behaves like a fluid attached to a sphere spinning at 1,000 mph and hurtling around the sun at 6,500 mph, with the amount of solar radiation reaching the Earth changing subtly instant by instant.

Still, meteorologists keep climbing back on that bicycle, and Halpert said the climate center's forecasts have shown improvements. The government has been issuing winter outlooks since 1972. It also has been doing them for other seasons, but winter traditionally has drawn the most interest.

As for the commercial-sector winter outlooks, AccuWeather Inc. is expecting slightly above-normal snowfall around here; a mild December, about 2.5 degrees above normal; an average January, and a February that would be about 3 degrees below normal — or 9 degrees colder than last February in Philadelphia.

The Commodity Weather Group and WeatherBell outlooks are similar. Weather Concierge, the company that evoked the 1995-96 and 2009-10 winters, says that while temperatures will be near normal, it will be quite stormy in the Mid-Atlantic and Northeast.

Steven DiMartino, chief meteorologist at Weather Concierge, said that a burgeoning El Niño warming in the tropical Pacific is likely to energize an active storm track that could result in a sequence of coastal storms.

When the surface waters out that way get warm, that can be a big deal in the U.S.; weather generally travels west to east, and the warming generates strong upper-air winds from the west.

In long-range forecasting, however, simplification is the great enemy of reality. El Niño has been slow to take hold, although the Climate Prediction Center still says it is likely that it will be brewing during the winter.

And Paul Pastelok, AccuWeather's longtime long-range forecaster, says winter outcomes during El Niños and their opposites, La Niñas, have been decidedly mixed.

"Some of them haven't worked out the way they were supposed to work out," he said.

The same can be said for seasonal forecasts.