Edmonton's Hottest Days

On this blog we talk about Edmonton's winter days a lot. But we don't really talk about the summer that much.

Last year we did take a quick look at Edmonton's Heatwaves, and today we're going to dig a bit further into Edmonton's hottest days.

When does Edmonton get 30°C days?

This chart shows when throughout the year we have had days of 30°C or more, from 1880-2017.

The earliest in the year that we've had a 30°C was April 25th & 26th 1977, at 30.1°C and 30.3°C respectively. The only other 30°C day in April was April 29th 1939, at 31.1°C. The latest 30°C was on September 28th 1887 at 30°C, and since 1880 September has had a total of 25 days which hit 30°C.

This year we just had a 30.2°C on May 23rd 2018, and that one isn't shown in this chart. But in recent years getting a 30°C day in May has been fairly common - it also happened on May 31st 2017, May 3rd 2016,  May 6th 2013, and May 18th 2010.


But How Hot Were They?

Here is the same chart, but this time we are looking at the temperatrues as well as the dates.

Edmonton's warmest recorded day was 37.2°C on June 29th, 1937. We have also had one 36.7°C day on July 2nd, 1924, and three 35°C days in 1924 and 1933. Those were all more than 80 years ago, though.

In recent years 34°C is the warmest that we've hit: in 2015, 2008, 2006, twice in 2002, and 1998.


30°C days by Month

This chart shows the breakdown of which months get the most 30°C days.

Not surprisingly July is the clear leader, with 237 days in the last 137 years, or about 1.7 each year.

May's 47 days in 137 years would mean an average of about 0.3 days per year, but we've now had one 30°C day in each of 2016, 2017, and 2018 so we're sitting above average.


Number of Hot Days Each Year

This chart looks at how many 30°C, 32°C and 35°C days we get each year, and also includes 25°C and 28°C days for a bit more context.

• In terms of 25°C days, 2014, 2015, 2016 and 2017 were all quite high ranging from 40 days to 52 days. And 2018 is off to an impressive start with 12 (as I write this) and it isn't even the end of May yet. That's way up from the last few years, where 2000-2013 only had 3 years with more than 40 25°C days, and there were 5 years (2000, 2004, 2005, 2010, 2011) which were down around 20 days. Looking at the 5-Year average for 25°C days right now we're at 42 days which is well above recent years, although way back in 1894-1898 the average actually hit 47 days.


• For 28°C days right now our 5-Year average is 12 per year. That's up a bit over the last few years, because around 2013 it was down at 10 days per year. But the average has been as high as 14 days a few times: 2010, the mid-1980s, the mid-1960s, the late-1930s, etc.


• For 30°C right now we average about 4 days each year, and that matches Edmonton's long-term average. In 2010 it was up at 6 days though, and in the late-1930s it was 8 days.


• 32°C days in Edmonton are pretty rare, and going back to the 1880s we've averaged about 1 per year, and that's where we sit right now. Edmonton's peak period for 32°C days was the mid-1930s, with 1933 recording 5 of them and 1936 recording 6. In recent years 2002 is the big standout with 6 32°C days.


• And as we saw in an earlier chart, all of Edmonton's 35°C days were recorded more than 80 years ago, with three in 1924, one in 1933, and one in 1937. (now is a good time to mention that I'm always a bit suspicious of the extreme readings from Edmonton's earliest 1880-1937 weather station.)

So are we seeing more hot days now than we used to? It doesn't look like it. Just in the last four years from 2014-2017 we've seen almost twice as many 25°C days as we did 5 years ago, and that puts us at the high end of Edmonton's range. But for the really hot days - 28°C, 30°C, 32°C - we're either at Edmonton's long-term average or a little below.

I've said many time before that Edmonton isn't necessarily getting warmer, but it is getting less-cold. And so this Hot-Days chart is an interesting comparison to the Cold-Days chart where we've seen the number of -20°C and -30°C days drops substantially since 1880. And even though our hottest days haven't changed much, our average temperature each year has been steadily increasing.


Hottest Day of Each Year

As we experience scorching May temperatures you might wonder: is that all there is?

This chart shows the date of the warmest day of each year (on the right axis), as well as the corresponding temperature (on the left axis). I normally try to avoid charts with 2 axes, but in this case I think it's useful to graph the temperature and the corresponding date together.

The earliest hottest-day was just two years ago on May 3rd 2016 at 30°C. And that's where the "Is that all there is?" pessimism comes from, because when we get a really warm May you have to wonder if this is as good as it gets for the year?

But then last year in 2017 we had a pretty late hottest-day on September 7th at 32.2°C. The very latest was on September 25th in both 1952 and 2011, and recently 2009 also peaked really late on September 23rd.

Of the 137 years here there were 15 which didn't have any days that hit 30°C: 1880, 1881, 1893, 1907, 1914, 1916, 1943, 1944, 1947, 1953, 1962, 1989, 1999, 2000, and 2005. The coldest hottest-day was technically 1881 at 26.1°C, although it's missing data for July and August so that's not correct. The 2nd coldest was 1916 at 27.2°C, and it isn't missing any data so we'll trust that one.. In recent years 1999, 2000 and 2005 didn't have any 30°C days, but their hottest-days were 28.8°C, 29.1°C and 29.6°C respectively.

Last week when we looked at Climate Hardiness Zones we saw that Edmonton's coldest temperature each year has been increasing fairly steadily. This chart shows how Edmonton's hottest temperatures each year have changed, and it isn't so dramatic. Right now our average hottest day is 32°C, and that's up from 31°C a century ago, but it's down a bit from 34°C in the suspiciously-hot 1930s.

The average date of the hottest-day (which is a bit of a weird concept) has bounced around between the beginning and end of July.

The animated version of this chart is nice for following the connection between temperature and date, but it's also a little crazy, so here's a non-animated version:

And that brings us to the end of our look at Edmonton's Hottest Days.