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Warmed Arctic, chilled Philly

If it’s so warm up there, why are we about to freeze down here?

Unlike the recent cool-down, what's coming the next two days is going to feel like a true Arctic blast.

Based on the forecasts, with temperatures failing to leave the 20s, Friday will finish among the top 10 coldest Dec. 16s in the 141-year period of record.

The frigid air coincides with this week's rather dire government report about "unprecedented" Arctic warming.

That's hardly a paradox.

Warming up in that region indicates a weakened "polar vortex," making that upper-level swirling mass susceptible to breaking off and migrating south, transporting cold air, says Judah Cohen, a scientist with Atmospheric and Environmental Research.

"I would definitely attribute this cold blast to a weakened polar vortex," Cohen said.

When the vortex is strong, it confines the cold to the polar regions.

Incidentally,  Cohen says the models indicate it should strengthen.

Based on that government Arctic Report Card, assembled by a research team and released Tuesday, the Arctic could use a nice chill-down about now.

Among the items that stand out is the amount of warming concentrated in the Arctic, which constitutes less than 7 percent of the earth's surface, said Mark Serreze, director of the National Snow and Ice Data Center.

Temperatures for the 12-month period that ended Oct. 31 were about 3.6 degrees Fahrenheit above the 1981-2010 period, the 30-year "normal."

Globally, the earth's surface temperature in the same 12 months was about 1 degree above that normal, according to the National Centers for Environmental Information.

Serreze says the warming likely is a mix of greenhouse warming and natural variability. "I would say it is somehow a combination," he said Wednesday.

The loss of ice and snow means a decrease in solar heat-repelling albedo, which accelerates warming.

Plus the Arctic has been awash in warming winds from the oceans, particularly the Atlantic, he said.

As one might expect with heat waves in summer, the planet's background warming probably is enhancing the effects.

Whatever the causes, the warming in Arctic is as real as the cold will be for the next few days.