Glenn's Blog: Will the Unseasonable Warmth Continue in December?

READ Glenn's Long-Range Winter Forecast HERE


It’s the 2nd  warmest November on record in Philadelphia. The month has been 5-6 degrees above “normal," which was only beaten in 1931. Highlights of the month:

  • NO days with temps below freezing
  • 19 days reached at least 60 degrees
  • Only three days had temps below normal
  • Not even a Trace of snow officially

(My forecast was right on target-see below).

The overall outlook is WARM and DRY. I expect temperatures to average 4 to 6 degrees above “normal” (or long-term average). As for precipitation, let’s say ½ to 1 inch below normal. And, oh yes, no measurable snow.

And it’s not just around here. Look at the most recent map of temperatures compared to normal across the U.S. (the bottom map):


As extreme as it’s been in the Northeast U.S., with 4-6 degrees above normal, it’s been even more extreme in parts of Minnesota and Wisconsin, with temperatures more than 8 degrees above normal. That is the same as if EVERY day of the month had temps 8+ degrees above normal! And the warmth covered the entire eastern half of the U.S. Only seven western states were cooler than normal.


The overall pattern shows no sign of changing for the next couple of weeks, at least.  Let’s go out a week to December 7th, and predicted temperature anomalies (compared to normal):


The relative warmth across the northern U.S. continues, and the anomalies are highest in Southern Canada. That area has to cool down a LOT before any serious cold can invade our area. And that means air coming down from Central or Northern Canada. How can that happen? It would take a “Blocking Pattern” such as a negative AO (Arctic Oscillation) or NAO (North Atlantic Oscillation), as discussed last month.

For that, we look way above the surface. The map below is for 18,000 feet up for Dec. 7th. There is no evidence of any kind of blocking pattern developing. That high up, winds blow parallel to the lines, so we can trace back from Phialdelphia to see where our air is coming from. Just as we saw earlier in November, it’s coming from the Central Pacific. No Arctic (or even Canadian) air comes in from that direction


The blue colors represent below average pressures, and the reddish colors are the opposite. To get a blocking pattern, we’re looking for some red colors on top of the blue, and there’s nothing close to that. It means a strong westerly jet stream racing across the Pacific, flooding most of the U.S. with unseasonably mild air. That’s for at least the first half of December overall. We’ll keep checking to see if any of those blocking patterns show any sign of developing……


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