Year-end special: December warming trend

With a high Wednesday expected in the mid-60s, about where it should be in mid-April, officially November will finish about 2.5 degrees above normal in Philadelphia.

December is expected to get off to a generally mild start, with a cool-down possible next week.

We can predict with high confidence that December won’t match the other-worldly warmth of December 2015, when the average temperature was 13.7 degrees above normal, rivaling that of the month before, which was one of the warmest Novembers on record.

But if the meteorological adage “the trend is your friend” holds any water, snow, or ice, place your bets on a mild end to the year.

Local warming has tracked fairly closely with global trends; in the last 30 years, Philadelphia's annual temperatures were 1.5 degrees above the 20th Century average.

However, for whatever reasons it has been particularly concentrated in December, especially in the last decade.

Nine of the last 10 Decembers have had average temperatures above the 20th Century average for the month, 36.2. The last 30 have a composite 38.5 average.

That’s a full degree warmer than the 37.3 degrees of its nearest competitor, the 30-year period that ended with the 1930s.

As for the last 10, the average through 2015 was a rather astounding 40.6, besting the 10-year period that ended in 1999, 39.3.

At the other end of scale, not surprisingly those very cool 1960s constituted the chilliest 10-year period for Decembers, with an average of 33.1 for the decade that ended in 1969.