136 Years of Walking Uphill Both Ways

Last week I looked at the number of warm days in a typical Edmonton winter, and found that it hasn't changed much in the last century. In the 120 days between November and February we get about 49 days above freezing, and 100 years ago that number was 48. Some decades have had more and some have had less, but on the whole it has been surprisingly consistent.

Today we'll look at some of the ways that winter has actually changed, although I think there are some surprises here too.

Even though the number of warm days hasn't changed much, the daytime high and low temperatures have been increasing. Over the last century the highs have increased by 1.5°C, and the lows are up 3.5°C. In the 1880's the difference between the daytime high and low was 11 or 12 degrees on average, and now that gap has closed to 8 or 9 degrees.

I don't think that averages give a very good sense of what things were like day-to-day though, so for that lets look at temperature ranges again.

Here we have the cold, really cold, and really really cold days.

When I was looking at "warm" days, I'd used anything above freezing as the cutoff point. For the "cold" days I'm going to say that the starting point is -20°C. I don't necessarily love 0°C through -19°C, but -20°C is when the dog starts complaining, when it's maybe time to start thinking about plugging the car in, and when I really need to add layers for bikerides.

Today we get about 20 days below -20°C, compared to 49 days above freezing. That's maybe not the best ratio around, but it would seem tropical compared to the 1880s when it was 44 days below -20°C and 46 days above freezing.

This all seems pretty much as expected: the 10 year period with the most cold days was 130 years ago; the last 20 years have had the fewest cold days; and 100 years ago there would have been noticeably more cold days than are typical today.

One oddity is the winter of 1930-1931, which had only 1 day below -20°C. No other winter has ever gotten close to that. I had thought that 2015-2016 was special with its 6 days, but 1986, and 1995, 2005 and 2011 were all similar. 1930 is in a league of its own, and I'll have to take a closer look at it one day.

The breakdown of all the days below -20°C shows that the number of days in the -20°C to -25°C range has been very consistent, but the really cold days have been slowly disappearing. So generations of Edmonton grandparents weren't exaggerating - it really did used to get that cold.

Lows below -45°C were never exactly an everyday occurrence around here, but they would happen every few years up through the 1930's.

Through the end of the 1940's most years could expect a day or two below -40°C. Then those disappeared for 22 years, showed up again once in 1972, and haven't been seen since.

Currently it's been a little over 6 years since the last -35°C was recorded, on December 13, 2009. That isn't too unusual though, because there was a 7 year gap without a -35°C from 1997-2004, and an 8 year gap from 1954-1962.

The longest stretch without a -30°C was 5 years, from January 13, 1998 through January 21, 2003. Right now the most recent -30°C was last winter, on January 5, 2015.

Just personally, in 7 years of riding to work my low is -31.5°C, and that's not for lack of trying. I would love (/dread) to be able to claim a -35°C, but the weather hasn't cooperated.

So on the whole, Edmonton might not be getting much warmer, but it has been getting less cold.

The recent history though, is - once again - not something I would have guessed.

The reason that I started digging into Environment Canada's weather data earlier this winter was because I wanted to see if I could trust my memory. And it turns out that no, I can't.

For the past few years I have been enjoying (with some shame) what I had assumed were ever-more-Climate-Change-enhanced winters. Other than 2010-2011 these last few years have all seemed so mild. But looking back over the last 30 years, outside of a few nasty ones in the mid-1990's, this has been very typical.

I thought that 2015-2016 was exceptional, but 1986, 1999, 2005 and 2011 were all similar. And while 2014-2015 wasn't amazing, it seemed pretty nice at the time. But from the numbers I don't know that I'd be able to perceive any difference between it and the winters of the late 1980's.

So this has me wondering about a few things:
  • Is my November-February range wrong? It covers the extremes, but maybe the total length of the winter is what colours our perceptions.
  • Does the amount of snow matter most? I haven't looked at that yet, because Environment Canada's precipitation numbers are a little tough to work with. 
  • Do we only remember the really rough winters, and those set low expectations? 
  • Did the closure of the municipal airport to scheduled flights in 1995 do something strange to the temperature readings?
I'm reaching a bit with that last one, but I'd always intended to compare the data from Blatchford against some other stations, and I may have to do that sooner rather than later.

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