Warm Decembers

November of 2017 was pretty cold, and so a few weeks ago I asked the question: Does a cold November mean a cold Winter? And the answer appeared to be "not really." We looked at the winters since 1980 which had cold Novembers, and about half of them were warm and half were cold.

But since late-November the temperatures have flipped, and December has been very warm. I'm a pessimist, and so now I'm worried that a warm December means that winter is really going to wallop us in January and February.

Today we ask the question: does a warm December mean a cold winter?

December 2017 at the mid-point

This chart shows how warm or cold a month is, relative to the 20th century average. The calculation is very simple - it takes the average temperature for all of the days in a month, and compares that to the average for that month for 1901-2000. We first looked at it in How Warm is 2017 - the Months, and then again in Cold Novembers.

We're only halfway through the month and so this chart isn't really fair, but right now December 2017's average temperature is more than 10°C above the 20th century average. There is still plenty of time for that number to drop before the end of the month, though. Assuming that the rest of the month is just average then that number would fall to about 5°C above the 20th century average.

So for right now we shouldn't make a big deal of the number, but we do know that December 2017 has been very warm, and that even if we do get a coldsnap it will still have been a warm month.

Other Warm Decembers Since 1980

This chart shows 10 other Decembers since 1980 that were 4°C or more warmer than the 20th century average.

The years here are 1985, 1986, 1987, 1993, 1997, 1999, 2002, 2005, 2006 & 2011. They range from 2005 at 4.4°C above the 20th century average, up to 1999 at 7.8°C and 1997 at 7.9°C.

We'll break these up by decade to take a closer look.

2000s & 2010s

Since 2000 we've had 4 other particularly warm Decembers, and they are shown here.

The main reference point of these charts - the "0" line - is to the 20th century average. But the dotted line shows the 5-year average, and that is maybe a more relevant comparison because it shows how these months compared to their neighbours.

• 2002-2003: January-May were all a little bit cooler than the recent average, but nothing extreme.


• 2005-2006: A very warm January, a cool~ish March, and the rest were pretty typical.


• 2006-2007: Another warm January, cool February, warm March, cool April.


• 2011-2012: Really warm across the board.

1990s

This chart shows the 3 winters with warm Decembers from the 1990s:

• 1993-1994: Of the 10 winters here, this is the only one that took revenge for its warm December, with a cold January and a really cold February.


• 1997-1998: Cold January but warm after that.


• 1999-2000: January was a little cool, and everything else was pretty typical.

1980s

And finally, the 1980's had a string of warm Decembers in 1985, 1986 and 1987.

• 1985-1986: Really warm January, cool February, warm March.


• 1986-1987: Really warm January and February.


• 1987-1988: Pretty warm across the board.

Summary

When we get unseasonably warm winter weather in Edmonton it's natural to worry that we will pay for it again later, and that winter will have its revenge.

But of the 10 recent, warm Decembers that we've looked at here, the only one that was followed by a particularly cold winter was 1993-1994. For the rest of the winters there were 5 that were genuinely warm (1985-1986, 1986-1987, 1987-1988, 2005-2006, 2011-2012), 2002-2003 was just a bit on the cool side, and the others were pretty average for circa 1980-2016.

And in these 10 winters there was only one "revenge" month, with February 1994 at -7°C below the 20th century average. A few of the other months here were a bit on the cool side, but there was nothing else extreme.

When we'd looked at cold Novembers we saw that about half of the time the rest of the winter was cold, and for the other half it was warm. I'd sort of expected to see the same even split today, but at least based on these recent examples it's pretty rare for a warm December to be followed by a cold winter.

I've said before that this blog is not about predictions, and I will not claim to know what 2018 has in store for us. This is winter, and this is Edmonton, and so undoubtedly the temperatures will cool off, and undoubtedly there will be some coldsnaps in our future. But if you're worried that winter will demand payback for this warm December, you probably don't need to worry.