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Could be a cold start ahead for winter

The signs - Siberian snow, potential atmospheric blocking near Greenland - suggest chilly temperatures as winter moves in.

by Tony Wood

As noted, Philadelphia just experienced its coolest Nov. 1-10 period since 1976.

From Oct. 30 through Nov. 10, the daily average temperature finished below normal for 12 consecutive days, and that hadn't happened since a 12-day stretch that ended on April 3, 2011.

With the month about half over, and temperatures averaging about 4 degrees below normal, November has a chance to break an impressive streak.

Officially, Philadelphia hasn't had a below-normal month since January 2011.

Looking ahead, temperatures look to average a shade below normal this week, and perhaps next, and some of the signs now point toward a cold start to December.

In its morning briefing, the Commodity Weather Group noted that forecast models favor atmospheric blocking near Greenland, suggesting that the meteorological winter would begin with a distinct chill.

In its very extended outlook, for the first week in December Accu-Weather is going with temperatures more characteristic of the first week in January.

One indicator to watch is the Eurasian snow cover. As we've noted, Judah Cohen at Atmospheric and Environmental Research Inc. has docmented a possible link between Siberian snow cover in October and our winter. Here is his paper.

In October, the Eurasian snow cover was at its 10th highest October extent in the 45-year period of record. For all of North America, last month was No. 8 among all Octobers.

Weather and climate, as we know, are immensely complex, and linear relationships are wanting.

We will note that the aforementioned 1976 remains king for Eurasian snow cover, and that preceded an historically cold winter in Philly.

But No. 4 on the all-time October list would be 1972, which was followed by the only winter on record in Philadelphia without measurable snow.

For monitoriing the progress of snow cover and for archival data, we highly recommend checking out the Rutgers snow lab, overseen by the Snow Man, himself, Dave Robinson, and this government site.