- we're going to be talking about average temperatures for each summer, rather than hottest temperatures. And that's why today is "warmest" summer rather than "hottest". (although we will take a quick look at the really hot days at the end)
- "summer" is also a little tough to define, and for the most part we'll be using a 5-month window from May-September. But we'll also see how things change if we restrict that to just June-August.
In previous posts we've looked at Edmonton's warmest years and warmest winters, so we're going to start with a quick review.
Warmest & Coldest Years
This chart shows Edmonton's Warmest & Coldest years. The format is based off of a chart that the National Oceanic & Atmospheric Administration uses to show global temperature anomalies, and we first looked at it back in Edmonton's Warmest Years.
That original post has the full explanation of what is going on here, but the short version is that this averages all of the temperatures for an entire year, and then compares that to the average for the 20th century. Edmonton's very warmest years - 1981, 1987, 2016 - were on-average 3°C warmer than the 20th century average. Because we're talking about averages that 3°C was spread across all 365 days of the year, and so most days would have been warm, but there would have been some cold ones too.
Warmest & Coldest Winters
This chart is the same style as the last one, but here we're just looking at November-March, or what we'll call "winter". We first used this chart in Edmonton's Warmest & Coldest Winters.
Edmonton's warmest & coldest years range from 3°C above the 20th century average to -4°C below it. When we switch to winters that range almost doubles, from 5°C warmer down to 6°C colder. Edmonton's range of potential temperatures is quite a bit larger during the winter (roughly -45°C to 15°C) than it is during the summer (5°C to 35°C), and so a warm winter can be really warm, while a cold one can be really, really cold.
And that brings us to...
Warmest & Coldest Summers
And here are Edmonton's warmest & coldest summers, based on the average temperatures for May-September.
The warmest summer was 1998, at 2.3°C above the 20th century average. And 2nd and 3rd place were the past two summers, with 2017 at 2.2°C and 2016 at 1.9°C respectively. The top-10 warmest summers include a lot of recent years: 2006, 2012, 2013, 2015, 2016 & 2017.
The line for the 5-year average follows a squiggly path over the years, but around 1950 it popped-up above the 20th century average and it has stayed above ever since. And in the past decade-or-so we've had quite a few warm summers, and so that line for the 5-year average has trended sharply upwards.
2018 so far...
This chart is just a reminder of what our High temperatures have looked like so far this summer. Red is above the recent average, and blue is below.
The orange circles represent anytime that we set a recent (since 1996) record, and there were 8 in May, 6 in June, 2 in July, and now 2 in August. And one of those August days was also an all-time record, with August 9th hitting 34.5°C. That one is circled in red, and then just a few days after that we set an all-time coldest High, on August 12th at 11.6°C. (just a reminder: broken records aren't all that uncommon)
So this summer has been a lot of days above the recent average, but how does it compare to other summers?
For a full explanation of the data in this chart it's easiest to refer back to the original discussion of it in How warm is 2016? (September Edition). Generally though, it tracks how much warmer each day of the summer was compared to the 20th century average - warm days get points and cold days lose them.
The blue and orange background is the range of all the years going back to 1880, and they are grouped together like that because showing each individual year gets too messy. The last 10 summers are shown here as individual lines, and 1998 is also included because it's currently in #1 spot.
And how does 2018 compare? It's shown in red, and the warm May pushed it out to large lead, and since then it has kept pace with the other warm years. We don't know what the rest of August and September have in store for us, or if it will stay in 1st place. But wherever 2018 ends up it is fairly likely that it will rank as yet another very warm recent summer - along with 2017, 2016, 2015, 2013 and 2012.
(it is worth pointing out that 2018 as a whole won't be a particularly warm year. It had a typical January & February, but a really cold March & April, and then the really warm summer.)
Summer vs. Winter
One thing to keep in mind is that a warm summer isn't quite as extreme as a warm winter.
This chart puts winters and summers together on the same scale. The warmest winters have been 5°C above the 20th century average, whereas the warmest summers were at 2.3°C above. And so the summers are a little bit tiny compared to their winter counterparts.
The reason that the summers are less extreme than the winters just has to do with the temperatures that are possible. In this chart the orange and light-blue areas show the range of where temperatures have fallen in the last two decades. The red and dark-blue lines are examples of what a really warm summer and winter looked like.
The summer of 2017 in red was Edmonton's 2nd warmest, and it spent a lot of time above the average. But a hot day during the summer is around 30°C, while a cold one is around 15°C. The biggest possible gap between warm & cold Highs is only about 15°C or 20°C.
For the winter of 2015-2016 in blue, it also spent a lot of time above the average with days around 5°C and 10°C. But those warm days were about 30°C warmer than a cold High during the winter, which could be down at -20°C or -25°C.
So that's why the chart for the warmest & coldest winters is more dramatic than it is for the summers.
This is a chart which we first looked at in How Warm is 2017 - the Months and it shows how much warmer each month of the year was compared to the 20th century average. We've put curtains on January-April and October-December to focus on the summer months.
There's a lot going on in this chart, and a lot of variation from year-to-year. But there are two things to watch:
- The dotted grey line for the 5-year average creeps upwards over the years.
- The warm summers which we've talked about - 1998, 2006, 2012, 2013, 2015, 2016, 2017 - had most or all 5 of the individual months above the 20th century average.
- The really warm & cold summer months all stay within ±4°C of the average, whereas the winter months can be at ±8°C or more.
#1 1998
#2 2017
#3 2016
#4 2006
May-September or June-August?
So far today we've been using May-September as "summer". That's my personal preference, because May and September can both be pretty summer-like: May 2018 was almost as warm as July; and September 2017 had plenty of warm days. So May and September can have a big impact on how long summer feels, and whether we get 3 months of it, or 4, or maybe even 5.
But you might still be wondering how our "true" summer months of June-August have changed over the years? That's what we have in this chart.
When we shorten the timeframe to June-August the overall picture doesn't change too much, but some of the warm/cold years move around a bit. In particular 1998 falls from 1st place for May-September down to 6th place June-August, while 1961 steps into the top spot.
The top-10 still contains a bunch of recent years: 2006, 2012, 2015, 2016 and 2017. And the 5-year average still takes a sharp step upwards in the last decade.
Now, you might think that Edmonton is a big city, and that its summers are naturally get warming because of the heat island effect? So in this chart we're looking at three outlying stations: Calmar, Campsie, and Sion. We've previously used these for reference in Frost-Free Days: Part 2 and Rural Alberta & the Heat Island Effect.
We use these 3 particular stations because they each have about 90 years of continuous data. Unfortunately that's not as many years as Edmonton has, and that's why these rural data series are truncated a bit in this chart. The "20th Century Average" for the rural stations is also a bit iffy because it's missing 1901-1915. So this isn't perfect, but it's the best that we can do.
With the rural stations we see a trend that's similar~ish to Edmonton - cold summers a century ago and warm summers more recently. And all 4 of these stations had 1998 as the warmest summer. There are some differences though - Sion notably had a series of really warm summers in the 1940s.
Unfortunately none of these stations have data continuing to 2018, so we don't know if they had the same recent uptick that we've seen in Edmonton.
Calgary, Winnipeg and Montreal
For one more set of comparisons here we have Calgary, Winnipeg and Montreal. We've previously looked at the warmest and coldest winters for these cities in 2017-2018 Winter-in-Review: Winter City Showdown - Part 2.
Since this blog is Edmonton Weather Nerdery we won't go into these other cities too much, but a few quick points:
- Calgary's warmest summer was 2017, and 1998 was in 7th place. In recent years it has seen a similar uptick to Edmonton, with 2006, 2012, 2013 and 2017 all in the top-10. But it also had a clump of warm summers in 1914-1922 (with 1922 in 2nd place) which don't show up in the Edmonton data.
- Winnipeg's warmest summer was 1988, which wasn't particularly notable in either Edmonton or Calgary. Winnipeg's recent summers have been warm~ish averaging 0.7°C above the 20th century average, but 1919-1923 were really the high point for Winnipeg.
- Montreal's warmest summer was 1999, with 1998 in 8th place. Recently it's also had several warm summers, with 2011, 2012, 2015 and 2016 all in the top-10.
The "Hottest" Summers
So far today we've looked at average temperatures for the summer - the daily Highs & Lows. This chart switches things up, and just looks at the hottest High temperatures.
So far in 2018 we've had 7 days which hit 30°C. That's more than our average of ~4ish, but in recent years 2017 had 6, 2015 had 9, 2008 had 8, 2007 had 8, 2006 had 9, 2003 had 7, and 2002 had 13. So the 7 so far in 2018 is definitely more than normal, but it's not particularly extreme.
Edmonton's peak timeframe for 30°C days was actually back in the 1930s: 1932 had 10, 1933 had 13, 1936 had 11, and 1936 had 11. In those years the 5-year average for 30°C days hit 9.6 days per year, when normally it's ranged between about 2-5 days. How do those "hot" years compare to "warm" years?
In this chart those abnormally hot 1930s years are circled in red, and a few of them are up around the 0.7°C range, but they don't compare to the other warm years.
Edmonton's year with the most 30°C days was 1961 though, with 14. And as we saw earlier it does rank as #1 warmest summer when we're just looking at June-August. And for 1998 - our other #1 warmest summer for May-September - it only had 3 30°C days.
Calgary, Winnipeg and Montreal - Hot Days
And finally for today, in this chart we're taking a look at the number of hot days that our favourite comparison cities get: Calgary, Winnipeg, and Montreal. This chart cycles through 25°C, 30°C, and 32°C days each year, and it's showing the 5-Year average for each city because the individual years bounce around too much.
For 25°C days:
- We've seen that Edmonton averages around 35 days per year, and Calgary's line in red has followed that very closely since about 1930. Although for some reason in the 1890s and the 1920s Calgary recorded a lot more 25°C days than Edmonton did.
- Winnipeg in green is way up there with an average of around 60 25°C days each year, and that has stayed fairly constant since 1900.
- Montreal in purple is now averaging around 70 25°C days each year. From 1940-2000 it was closer to 60 days, but in the last 20 years the average has increased.
For 30°C days:
- Edmonton and Calgary have a similar number of 30°C days, averaging around 4 each year. Calgary did have 14 in 2017 compared to only 6 in Edmonton, but in 2018 both cities are at 7 so far. And in the 1920s we again see that Calgary recorded a lot more hot days than Edmonton did. From 1914-1924 it had 7 years with 17 30°C or more, which was more than Montreal, and close to Winnipeg.
- Winnipeg averages around 13 30°C days each year, and that's actually down a bit from the 1970s-1990s when it was at around 16 days.
- Montreal averages around 12 30°C days each year. In the 1950s it was a little bit higher at 14 days, but in the 1960s-1990s it was down around 9 days.
For 32°C days
- Edmonton and Calgary are similar, averaging 1~1.5 32°C day each year. And again, around the 1920s Calgary recorded a lot more - 1914 had 10, 1918 had 9, 1919 had 11 - with the average reaching as high as 6 per year. That was more than Winnipeg or Montreal.
- Winnipeg averages 4 32°C days each year, although in the 1940s it was as high as 12.
- Montreal is just a bit below Winnipeg, averaging about 3.5 32°C days each year. That's up a bit from 2005, and overall is pretty high for Montreal.
We won't do a chart for 35°C, because Edmonton and Calgary almost never have them - Calgary recorded one this year for the first time since 1984; and Edmonton hit 34.5°C this year but our last 35°C was in 1937. They're pretty rare in Montreal too, with 2 this summer, 1 in 2011, 1 in 2002, and etc. In Winnipeg they're a bit more common, with 2 this summer, 1 in 2016, 2 in 2012, 1 in 2011, 2 in 2007, and etc.
Summary
Today was the first time we've looked at warm/hot summers, so it was a bit of a kitchen-sink approach as we pulled out ever chart that we could.
When we look at average temperatures Edmonton has recently had a string of very warm summers. Edmonton's warmest summer was 1998, but 2017 and 2016 were 2nd and 3rd, and 2015, 2013, 2012 and 2006 were all in the top-10. And it looks like 2018 will probably be added to that list.
At some of Edmonton's outlying stations we saw a similar pattern, with summers generally warming up over the last century. Those stations were missing data for the most recent years though, so we don't know if the last decade-or-so has been as warm for them as it has been for Edmonton.
When we look at Calgary, Winnipeg and Montreal, Winnipeg's summers have been pretty flat recently, but both Calgary and Montreal have seen several recent top-10s. For the number of really hot days each year all of those cities are still near their historic ranges.
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