2016-2017 Winter in Review - The Really Cold Days

In the next few weeks I'll be doing some recaps of this past winter - temperatures, snow, etc. Today we're going to get a headstart on that by looking at the number of really cold days that we had over the last few months.

One could quibble that "winter" isn't over actually yet. We will almost certainly get some more snow in April and maybe even in May (95% of the time, and 59% of the time respectively), but we have probably seen our last -20°C of the winter. The forecast for the rest of March is warm, and the last time that Edmonton dropped to -20°C during April was back in 1982. So while nothing is impossible, it's probably safe to say that our deepfreezes are behind us.

So we'll start with something that's close to my heart - winter commuting:

Active Commuting

This chart needs a bit of explanation, because it's not a count of all the cold days (we'll get to those in a bit), but is an attempt to estimate the number of really cold trips for anyone who walked, biked or bused through the winter. The idea behind it goes all the way back to the first real post that I wrote for this blog.

So this chart uses weekday temperatures only, and counts morning and afternoon trips. When I head to work on winter mornings it is typically very close to the daily low temperature, and heading home will be close to the high. The reason that weekends are excluded here is because on really cold weekends I can hide inside if I really want to, but for really cold weekdays I still have to go to work. I haven't removed the statutory holidays here though, so this could still be a bit on the high side.

With all of that then, we can see that 2016-2017 was pretty typical. Over these 5 months, there wold have been 5 trips below -25°C and another 13 below -20°C. That puts it very close to 2006-2007, 2009-2010 and 2012-2013. It had a few more cold trips than 2014-2015, but it didn't have any trips below -30°C like 2011-2012, 2013-2014 and a few of the others.

The standouts winters here are 2015-2016 as the warmest and 2010-2011 as the coldest. The very mild winter of 2015-2016 had only 2 weekdays that dropped below -20°C. And 2010-2011 would have had 46 commutes below -20°C, or about one-quarter of the entire winter.

Now lets add weekends back into the mix, and take a look at the total number of cold days:

Cold Days

Here we have the total number of days each winter where the temperatures dropped below -20°C.

I've mentioned my dog before, and that -20°C is the point where she needs to put boots on for walks.
The winter of 2016-2017 had 25 days below -20°C, which to me represent at least 50~75 separate struggles to get the dog into her boots, which is quite frankly too many.

Again though, we see that 2016-2017 was pretty typical, if maybe a little bit on the high-side of things. Last winter 2015-2016 was very mild, but 2011-2012 wasn't actually too far off from it. And 2010-2011 was a harsh winter, although 2008-2009 had more really, really cold days below -25°C. And that all lines up fairly nicely with what we saw last week in Edmonton's Warmest & Coldest Winters.

Right now the last time that we had a -30°C was three winters ago, back in January 2015. There was a similar 3-year gap from January 2005 to January 2008, and Edmonton's longest stretch without a -30°C was actually 5 years, from January 1998 to January 2003.

History of Cold Days

Here's the same data, but with a longer-term outlook going all the way back to the first records from the 1880s. It shows the number of days each winter below -20°C, -25°C and -30°C, and the 5-year averages appear as a dotted, red line.

From the 5-year averages we can see that the number of cold days in Edmonton have been dropping - a big initial drop from the 1880s (when the measurements were maybe questionable?) into the 1890s, and then a fairly consistent drop since about the 1950s.

Right now we average about 25 days below -20°C each November-through-March, which includes about 5 days below -25°C, and maybe 1 below -30°C.

Earlier I'd mentioned that from 1998 to 2003 there was a 5-year gap with no days below -30°C, and you can see that here if you look closely. Just before that though, there was a short period from 1994-1997 when the number of really cold days spiked. In particular the winters of 1995-1996 and 1996-1997 had 13 and 10 days below -30°C respectively, which is basically double any other winter going back to the 1970s.

That's it for today. This weekend I'll be back with the regular March Review/April Preview, and then in April we'll continue on with the 2016-2017 Winter in Review.