Winter outlook: Snowy, after balmy start

Posted: December 02, 2012

With November's ending a remarkable streak of warm months in Philadelphia, meteorologists are saying they expect the next few months to be eventful, chilly, and snowy.

By the time the snow season is over, from 25 to 30 inches of snow could land atop the region, with plenty of panic opportunities.

That's the consensus based on a handful of preseason outlooks, and it would be six to seven times more snow than last season.

But experience indicates that actual results may vary.

As usual, the forecasts, along with the temperatures, likely will rise or fall with atmospheric developments over the North Atlantic Ocean that aren't predictable beyond several days.

And so far the atmosphere hasn't been showing its hand.

In fact, although the meteorological winter began Saturday, it will begin to feel a lot like Halloween this week, with temperatures approaching 60 Sunday and surpassing that level Monday and Tuesday.

In mid-November, December had shown signs of coming on cold. At the time, AccuWeather's extended forecast called for the first week in December to have January-like temperatures.

For now, although it has not listed a specific amount, AccuWeather is on record as calling for above-normal snowfall in Philadelphia, where the seasonal norm is 22 inches. (Last year's paltry total: four inches.)

AccuWeather alumnus Joe Bastardi, now with another company, Weatherbell Analytics, sees 25 to 30 inches, within scraper distance of the 24 to 32 projected by Cecily Tynan at 6ABC.

Glenn Schwartz, meteorologist at NBC10, is more bullish on the white stuff, saying odds favor 30 to 35 inches.

If the atmosphere is being chary with clues, what is the basis for these guesses?

Schwartz sees hints in the colder regions of the planet. During October, air-pressure patterns in the North Atlantic frequently favored cold and storminess in the Northeast. If those alignments were to repeat during the winter and become locked into place for extensive periods - a phenomenon known as "blocking" - that could mean snow and cold around here.

Blocking was prevalent in the winters of 2009-10 and 2010-11, when more than 10 feet of snow buried the region. One hypothesis is that the blocking, ironically, may be related to melting Arctic sea ice. The atmosphere is interacting with open water up that way for the first time since humans have been paying attention, and that could be affecting pressure patterns that in turn affect Philadelphia's weather.

October snow cover in Siberia was well above normal, an indicator well-correlated with colder winters around here, according to Judah Cohen at Atmospheric & Environmental Research Inc. in Lexington, Mass.

That might have had some effect on the local weather in November. The average temperature for the month at Philadelphia International Airport came in at 44.2, 3.5 degrees below the 30-year normal and the coolest since 1996.

That breaks a streak of 22 consecutive months, dating to January 2011, of above-normal monthly temperatures.

Such a combination of a warm October and chilly November is unusual, noted Tony Gigi at the National Weather Service office in Mount Holly.

He found only six similar cases, and on average, and for what it's worth, in them both the average winter temperature, 35.4, and snowfall, 22.4, were almost perfectly normal.

Not that the weather will be.


Contact Anthony R. Wood at 610-313-8210 or twood@phillynews.com.

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