First -20°C of the Winter

Christmas Eve has brought us the first temperatures below -20°C for the winter of 2017-2018. Today is going to be a trivia day, as we look at when the Lows first drop below -20°C. (we also looked at this a bit last year in 'Tis the season of -20°C)

Date of the First -20°C

Here we have the recent history of the first -20°C Low of each winter.

This year we had 3 days at -18°C during November, including one way back on November 4th. But we didn't break the -20°C barrier until December 24, which makes 2017 the latest since 2002.

Recently mid-to-late November or early-December has been pretty common for the first -20°C, but in 1997-2002 we had a string of late years with the dates in December and even into January.

History

And here we have the entire history, going back to 1880.

November has been pretty popular all along, although there have always been some years that stretched into December, and even 7 that waited until January. In the 1920s-1940s there were also half-a-dozen years years where -20°C showed up in late-October.

The red line that appears in this animation is the 10-year average date.

10-Year Average

Looking at the 10-year average, right now we actually average about the same date that we did 120 years ago.

The average dipped into mid-November in the late-1920s and early-1930s, with a string of really early years. And in the early-2000s it shifted into mid-December, after the 1997-2002 stretch of late years. But 2010-2014 were all between November 13-19, and that's pretty early even compared to history, and so our average is sitting just a few days behind where it was in 1890.

We shouldn't necessarily read too much into that, though. At the top of this post I said that today was about trivia, and that's just because -20°C is an arbitrary cutoff. I like to use -20°C as a reference, but we got really close to it almost two months ago now. The fact that -20°C didn't show up in November is as much about luck as anything, and that could apply to any of the years here to one degree or another.

Now does seem like a good time to mention that while the date that -20°C first arrives hasn't changed too much, the number of times that we hit -20°C has dropped:

Total Number of Cold Days

This is a chart I've used several times before - most recently in 2016-2017 Winter in Review - The Really Cold Days.

It shows how the number of really cold days each year has been falling since the 1880s. Right now we average about 23 Lows below -20°C each winter, about 7 below -25°C, and maybe 1 below -30°C. It's always important to keep in mind that Blatchford is not the International, though. The temperatures from the International Airport are often much scarier than what we see in the city, and we looked at that in detail in Versus - The Edmonton International Airport: Part 2.