Edmonton's Largest Snowfalls

Last year we looked at how often Edmonton gets giant snowfalls, and from recent history we saw that we get:

• 10cm (4"): usually about 2-5 times per year
• 20cm (8"): maybe every-other-year
• 30cm (1'): none in the last decade, 3 in the last 30 years.

I was never completely happy with some of the charts in that original post, and so today we're going to take a second look.

Snowfall Events of 5cm or More

This chart shows every multi-day snowfall event with a total of 5cm or more, going back to 1880. Blatchford's snow records are shown in orange and they stop in 2006, and the International Airport's are in blue and they run from 1960 to today. 

One important distinction here is that this chart doesn't show one-day snowfall totals, but instead it takes consecutive days with snow and combines them into snowfall "events." The reason we're using this approach is because snow will often start in the evening and continue on through the morning. Environment Canada's numbers would split that across the two days, but it makes more sense to group them together. 

And so today we are going to define a Snowfall Event as: the total snow on consecutive days where each day received at least an inch (2.5cm) of snow.

There's also a caveat here for the "X Events" counter at the top of the chart, because it double-counts on days that Blatchford and the International both recorded large Events on the same day. I don't think that's a big deal since we're not trying to be particularly scientific, and we'll compare Blatchford and the International later on.

From this chart it's tough to discern any trends, and for that it's probably easiest to go back to the charts from last year:

This chart from last year shows the number of 10cm+ snowfalls each winter, and it hasn't changed much over time. There were a few years around 1900 with a lot of big snowfalls, but other than that 1-4 per year has been pretty typical.

In the post last year I think that we covered the trends (or lack thereof) pretty well. Today we're more interested in the big Events:

25cm or More

This version of the chart only shows the Events with 25cm of snow or more.

Edmonton's largest snowfall Events were: 

1. 47.5cm over 3 days, from April 18-20, 1955
2. 46.5cm over 5 days, from December 27-31, 1893
3. 43.5cm over 3 days, from April 1-3, 1948
4. 41.9cm over 3 days, from February 29-March 2, 1900
5. 40.6cm on 1 day, October 25, 1885, and 40.6cm over 2 days on April 6&7 1991.

Most of those are multi-day totals, with the only single-day snowfall being the 40.6cm on October 25, 1885. A few other big days were November 15, 1942 with 39.9cm; May 2, 1886 with 38.1cm; and October 16, 1991 with 28.6cm.

The most recent 25+cm snowfall Event was 25.9cm over 6 days from January 12-17, 2011. And since 2000 there were only 2 other big Events: 35.2cm over 5 days from May 2-6, 2003; and 28.1 over 2 days on April 14&15, 2002.

1995-2017

Here we're looking at all snowfall Events of more than 5cm, since 1995. Because there is a bit more space the labels on this chart are for anything greater than 20cm.

There are 4 Events here where both Blatchford and the International recorded more than 20cm of snow: November 10 1996, April 15 2002, January 20 2003 and May 6 2003. Those dates have both the orange text and the blue text.

There are 4 other 20cm Events that happened after 2007, and so only the International has any data for those.

And then finally there were 4 Events where Blatchford recorded more than 20cm but the International didn't (although it was close twice), and 1 Event where International broke 20cm but Blatchford didn't.

Blatchford vs The International

This chart shows the 46 years where both Blatchford and the International were recording snow data, from 1960 to early 2007. It cycles between both stations, Blatchford only and the International only.

We can see that there's a lot of overlap between the two. Across these years Blatchford recorded 351 of these large events, with an average of 10.9cm. At the International there were 361 events, with an average of 10.2cm.

But we'll end off with one more graph from last year:

Today we've talked about large snowfalls - in the range of 5cm, 10cm, 20cm and beyond. And this chart shows how often they happen. At both Blatchford and the International almost half of the time when it shows we get less than 1cm, and we only get more than 5cm about 16% of the time.