Heatwaves & Heat Islands: Part 2

We are back to talk about the heat island effect again today, and how heatwaves may or may not exaggerate the temperature differences between rural and urban stations.

In Part 1 we looked at the individual daily temperatures during 3 of Edmonton's most notable heatwaves - 2021, 1961, and 1924. On extremely hot days:

• The High temperatures for all of the stations around Edmonton are generally pretty close to one another.
• The Lows temperatures for the Blatchford station in Edmonton are generally several degrees warmer than at the outlying stations, but that occurred in all 3 of the heatwaves going back to 1924.

Today we want to see if there are any trends to be seen, and we will be focusing on a few Edmonton-area Environment Canada weather stations.

• Blatchford is in Edmonton, about 2km north of downtown with data from 1880-today.
• Campsie is 100km northwest of Edmonton with data from 1913-today. 
• Calmar is 40km southwest of Edmonton with data from 1916-2007.
• The International is 30km south of Edmonton with data from 1961-today. 
• Stony Plain is 40km west of Edmonton with data from 1966-today. 

Campsie is the most truly rural station of the bunch:

 

Summer Temperature History

To start with, here is the history of 10-year average temperatures for these stations for the "summer" months: from June 1st through August 31st.

Blatchford is the longest line in dark blue, and for the Highs temperatures it is mostly in the middle of the other stations. Stony Plain in Pink is the most recent station to start, and in the beginning its summer Highs were well below the other stations, although since about 2005 it has closed most of the gap.

For the Lows Blatchford is well above all of the other stations, with Stony Plain in the second spot. The Lows for Calmar, Campsie and the International are all clustered together.

In terms of trends the average summer Highs for most of the stations look pretty flat, with the exception of Stony Plain which has jumped up closer to the other stations. For the average summer Lows all of the stations have warmed, except for the International which has dropped 0.2°C since the 1960s. For the other stations Blatchford is up 3.9°C over 140 years, Campsie is up 2.5°C over 100 years, Calmar was up 2.2°C over 91 years, and Stony Plain is up 0.7°C over 55 years.

So in general the average summer Highs around Edmonton aren't all that much different than they were a century ago, but the summer Lows are up by 2.5~4°C. We talked about this more in Why Heatwaves Aren't the Whole Story. (also, today we are just looking at summer temperatures, but the temperature changes during the winter are much larger).

The word of the day is "Relative" because what we really want to know is how the temperatures at these stations have changed compared to one other. If the heat island effect disproportionately affects big cities, then theoretically Blatchford's temperatures should have warmed faster than the outlying areas.

Summer Temperature Comparison

This chart uses the temperatures at Blatchford as a reference, and it shows the average difference each summer (June 1 - August 31) for each of these stations. 

For the average summer Highs Calmar was actually a little warmer than Blatchford after around 1930. And as we saw earlier Stony Plain's Highs started 1°C or more colder than Edmonton, caught up to the city for 2010~2015, and then just recently have been 0.8°C cooler again. For Campsie and the airport the differences have bounced around, but similar to Stony Plain for the past few years they've been about 0.5°C cooler than the city. 

For the average summer Lows Stony Plain has been closest to Edmonton, at around 1°C cooler than the city since the 1960s. For the other stations the average Lows are now around 3~3.5°C cooler than the city, and that gap has grown by about 1°C since records started.

Is that ~1°C change the Heat Island Effect? It could be, although for Campsie and Calmar it looks like most of the change happened from 1915-1960, and things were pretty flat after that. In 1960 Edmonton's population was 269,314, and the city had a much smaller footprint than it did today.

For the airport it does look like the gap widened around 2000, but that's probably because the airport is weird. Here's the same chart, except that it is flipped to use the airport as the reference station:

Using the airport as a reference we are only looking at 1960-today. And around 2000 Blatchford did get warmer than the airport, but so did Campsie and Stony Plain. Stony Plain has urbanized and grown since 2000, but Campsie hasn't, so this is probably more about how notoriously cold the airport is, rather than the Heat Island Effect.

Summing up so far:

• Blatchford's summer Highs are pretty close to the neighbouring stations, and have been since 1915.
• Blatchford's summer Lows are 2~3.5°C warmer than the neighbouring stations, and have been since at least the 1960s. Going further back to 1915 Blatchford was still warmer, but by slightly less at maybe 1.5~2.5°C.

So now we know what the history of typical summer temperatures looks like. What about the heatwaves?

30°C Days Temperature Comparison

This is the same chart again, except this time instead of looking at the whole summer we are focussed on days where Blatchford's High hit 30°C. 

On thing to keep in mind with this chart is that we're dealing with a very small sample size. Edmonton averages about 4 30°C days each year, but many years only get 1 or 2, and some get none. And so each bar in this chart is the average temperature difference from only a handful of days. That's why for the Highs Campsie has 1 giant bar in 2011 for a single day when Blatchford hit 31.5°C, and Campsie was down at 20.5°C. Also, in this chart years which had lots of 30°C days will be an average of all of those days, and might look less extreme than single days. But we wanted to talk about what the Heat Island Effect looks like on Edmonton's hottest days, and these are the hottest days.

For the Highs the differences are pretty small, with Blatchford typically 0.5~1°C warmer than the other stations on these very hot days. And as for the question of how that has changed over time: it really hasn't, has it? Stony Plain has actually closed the gap with Edmonton by about 0.5°C, and the other stations are all around where they were 50 or 100 years ago.

For the Lows the differences are larger than the Highs again. Stony Plain is pretty close to Blatchford with overnight Lows about 1°C cooler on these hot days, and that gap has closed from 2°C 50 years ago. For the other stations the gap is in the range of 4~5.5°C, which is up from 2~3.5°C a century ago. Again though, for Calmar and Campsie most of the change happened from 1915-1960. For the International the gap has increased from 3.7°C to 4.6°C since 1960.

32°C Days Temperature Comparison

We can play this game one more time with 32°C days, which happen on average about every other year. 32°C days are uncommon enough that most of the bars in this chart represent the temperature differences on a single day (or maybe two) when Blatchford hit 32°C.

For the Highs, in recent years when Blatchford has hit 32°C:

• Campsie has generally been about 1.5°C, but sometimes it's or 3.5°C cooler, and a few times it has been warmer. Going back through history most of these bars are in the 0/1.5/3.5°C coller range (with 1932 as a standout at 7.7°C)
• The Airport has been 1.5~3°C cooler, which hasn't changed since 1960.
• Stony Plain has been 1~2°C, while in the 1970s & 1980s the difference was 2~3°C.
• Calmar doesn't have recent data, but from 1915-2007 it was in the 1~2°C range without much change.

For the Lows when Blatchford has hit 32°C:

• Campsie Lows are about 5~7°C cooler, which has been pretty typical since about 1960. Before that the difference was around 4~5°C.
• The Airport's Lows are also 5~7°C cooler, compared to 3~5°C in the 1960s & 1970s.
• Stony Plain's Lows range from 1°C warmer to 2.5°C cooler than Blatchford's. That is warmer than in the 1960s & 1970s when the difference was 4~5°C.
• And Calmar was in the range of 3°C for 1915 through 1960, and then 4°C for 1960 through 2007.

15°C Lows Temperature Comparison

One notable thing about the 2021 heatwave was the large number of warm overnight Lows which we had, so here is a final version of the chart for nights when Blatchford stayed about 15°C. Many of these dates will overlap with what we saw in the 32°C chart, but it's worth focussing in on those hot nights in particular. (once again though, this is a very small sample size)

And what do we see?

On those hot night the Highs at the outlying stations were generally ~1°C cooler than Blatchford, although there doesn't seem to be much of a change from 1915 to 1960 to 2021.

And for the Lows Blatchford was 2~5°C warmer than the other stations. Most of the stations look pretty flat, although with Campsie it again looks like the gap got bigger from 1940~1960.

You can also set the dashboard to show the really hot Lows like 17°C, or 19°C, but prior to 1960 there were almost none of those and so the history is shorter.

Summary

So what was the point of all of this?

This image shows the daily temperatures from the great heatwave of 2021. In the past on this blog we have repeatedly discussed how overstated the impact of the Heat Island Effect is. And yet...when I saw these temperatures my first thought was "Wow, that's some big Heat Island Effect."

But when we take a closer look, was this really the Heat Island Effect? The High temperatures were actually quite close across the region. And for the Lows Blatchford was definitely much warmer than neighbouring stations, but that has been the case since at least 1915.

So today leaves us with some unanswered questions. Blatchford is warmer than its surroundings, but that was also mostly the case a century ago, so what is going on? All that we can do is speculate, but a few ideas come to mind: 

• The downtown area might have a microclimate which makes it warmer than the surroundings. That might be why there is 8,000 years of history of Indigenous use of areas like Rossdale, rather than at a place like the airport? (disclaimer: I do not know anything about the Indigenous history of locations like Stony Plain or Campsie)
• Blatchford is still a big empty field with a few old runways, next to a freeway and a railyard. Maybe it doesn't actually feel the Heat Island Effect the way an downtown does.
• Maybe the Heat Island Effect's biggest impact is early on, when a city grows from 0-400,000 people. As a city spreads (or sprawls) outwards the Heat Island might affect a larger area, but it doesn't get more concentrated.
• Maybe the Heat Island Effect is really, really big, and even a location like Campsie 100km away still feels the majority of it.

That's all speculation though, and speculation is terrible. For all I know a Wizard did it. 

But I think there are 2 big takeaways from today:

• When we see a 5°C temperature difference between Blatchford and the airport, that does not mean that the airport is the "natural" temperature, and that the big city has warmed itself up by 5°C. The vast majority of that temperature difference also existed 50 or even 100 years ago. And we now know that is also the case during extreme temperatures like heatwaves.
  
  
• For the Calmar & Campsie stations with long histories it does look like the city's summer Low  temperatures got relatively warmer by about 1°C from 1915~1960, but then after that things flattened out.

Heatwaves & Heat Islands: Part 1

Today we are going to take another look at the Urban Heat Island Effect. This is the idea that cities are warmer than rural areas, and that cities are also warming faster than rural areas, because cities absorb, generate and concentrate heat.

Why is the heat island effect interesting?

• Every day in Edmonton we see temperatures from downtown, and at the airport. There is often a huge difference between the two stations: 5°C, or even 10°C. So it is really easy to get into the mindset that Edmonton is warm because it is a city, and that if the city were not here then the temperatures would match the Airport, because the Airport is the "natural" state. But it's more complicated than that.
• Climate change deniers like to use the heat island effect to dismiss climate change, and to say that all data is biased because of course cities are getting warmer and yadda yadda.

Today we will mostly be looking at the first point, although some of that will spill over into the second point too.

So the heat island effect is interesting, but why do we need to look at it again? Haven't we already done this?

The reason for today is because we just had a historic heatwave, and maybe the heat island effect looks different during extreme temperatures?

Heatwave 2021

This chart cycles through the daily High and Low temperatures for Environment Canada stations in the Edmonton area for June 24th through July 3rd. The main 30°C+ heatwave was June 25th through 2nd, but the 24th and 3rd were also pretty warm, so they're included here too. The dashboard with this daily data is here, but it's pretty slow so we will stick to images for a bit.

The Blatchford station near downtown is at the centre of the group of stations. For the Highs Blatchford was usually among the warmest stations, but several of the outlying stations like Namao and St. Albert had hotter days. And for cooler stations the International Airport's Highs were generally 1°C or 2°C below everywhere else.

For the Lows Blatchford was the warmest of the group for every night here, except for June 30th when it was below the Namao and Oliver stations in the northeast. For the nights when Blatchford was the warmest it could be 1°C, or 2°C, or even 5°C warmer than some of the other stations.

And this is where we fall into the trap: cities are warm, and so the reason that Blatchford is warm is because it's in the big city, right? Let's see...

Heatwave 1961

Here we have the temperatures for the great heatwave of June 1961. There are fewer stations, so this one is zoomed out a bit, and in the upper left corner is Campsie which is about 100km northwest of Edmonton.

For the Highs Blatchford's temperature was fairly similar to the other stations, and Fort Saskatchewan in the northeast had several of the hottest days, by about 1°C. For the Lows Blatchford was consistently warmest again, and again by anywhere from 1°C, to 2°C, to 5°C depending on the station and the day.

Heatwave 1924

And finally, here is the earliest of our recorded heatwaves, for June and July 1924. This time we only have records from 4 stations. 

For the Highs all of the stations take turns as the daily hot spot. For the Lows Blatchford is the warmest for most days, and again by anywhere from 1°C, to 2°C, to  5°C.

This set of charts isn't great for spotting trends, but just generally it looks like the temperature distributions around Edmonton weren't all that different for the heatwaves of 1924, 1961 and 2021:

• In 2021 Blatchford's Highs were similar to the neighbouring stations, and didn't get a boost just for being in the big city.
• In 2021 Blatchford's Lows were usually several degrees warmer than the outlying areas, but that was also the case in 1961 and 1924 when Edmonton was much smaller.

Campsie vs Blatchford Through History

In this chart we have the 20-year average temperature difference throughout the whole year between Edmonton and Campsie. It has 3 different time periods: 2001-2020, 1961-1980 and 1915-1934.

The dashboard with all of this data is here.

Campsie is a great station to use as a guinea pig because it has data from all of the way back in 1915 through today, and so we can get a sense of how things have changed over the (relatively) long term. 

For the average Highs Blatchford is warmer than Campsie, but only by a little bit. The average differences during the whole year were 0.1°C for 1915-1934, 0.5°C for 1961-1980, and 0.3°C for 2001-2020. The difference tends to be the greatest during the winter, but the Highs are pretty close overall.

The Lows look quite different from the Highs, with a big gap between Campsie and the warmer Blatchford. The average differences were 2.6°C for 1915-1934, 3.4°C for 1961-1980, and 3.3°C for 2001-2020. The difference in Lows is also more seasonal than the Highs, with some winter days averaging 5°C or 6°C warmer in Edmonton, while the summer days are mostly below 4°C.

Campsie vs Blatchford Heatwaves

This is the same chart that we just saw, except this time we are zoomed right into the heatwaves of 1924, 1961 and 2021. It looks a little bit less pretty like this, but this shows the individual daily temperature differences between Blatchford and Campsie.

We saw earlier that during the year Blatchford's High are on average less than 0.5°C warmer than Campsie's. That doesn't seem to change much during historic heatwaves, because for almost all of the days here there's only a fraction of a degree between the two stations. The one notable exception was the final day of the 1924 heatwave where Blatchford was 10°C warmer than Campsie. But generally the Highs are really close, and they were also really close in 1961 and 1924.

For the Lows Blatchford averaged 4.9°C warmer than Campsie in the 1924 heatwave, 6.6°C in 1961, and 5.8°C in 2021. All of those numbers are above the typical summer difference which is less than 4°C. But just among these heatwaves, Blatchford's Lows were extra-warm for all 3 of them, and didn't get a particular boost in 2021.

We are going to end things here for Part 1. For right now the take away is that:

• For the 1924, 1961 and 2021 the Highs for Edmonton and Campsie were generally very close (except on July 3, 1924).
• At first glance Blatchford's warm nights in 2021 definitely looked like the heat island effect at work. But the vast majority of that difference also occurred 97 years ago in 1924.

Digging into the daily temperatures for these 2 stations to look at 3 heatwaves spread across a century is definitely cherry-picking the data. In Part 2 we are going to take a step back to look at some larger trends.

The Great Heatwave of 2021

Is it reasonable to call the heatwave which lasted from June 26th through July 2nd (or maybe even June 25th through July 3rd) "unprecedented?"

(if you are reading this in the distant future some of the dashboards below may have updated to reflect new data or formatting, or they may be broken, or they may no longer make sense. To see the original images for this post refer to this twitter thread.)

Let's start with a quick list of what it didn't and didn't do:

• 8 days in-a-row hitting 29°C, beating 6 days from June 1961.
• 7 days in-a-row at 30°C, beating 6 from June 1961 again.
• 4 days in-a-row at 34°C, beating 3 from July 1924.
• 3 days in-a-row at 35°C, tying July 1924 again.
• 2 days in-a-row at 36°C, which had never happened before. Since 1880 Edmonton has only had 4 days reach 36, and 2 of them were June 29th & 30th, 2021.

It also set new daily records on June 28th at 34.2°C, and on June 30th at 37.0°C. 2 new records might not sound like a lot, but this heatwave overlapped with two previous heatwaves in 1924 and 1937:

In Edmonton's list of hottest days the week of June 29 through July 3 holds 7 of the spots, from 3 different years:

• At the very top June 29, 1937 remains as Edmonton's hottest day on record at 37.2°C. 
• 2021 has 3: #2 37.0°C on June 30, #4 36.2°C on June 29, and #7 35.2°C on July 1.
• 1924 has 3: #3 36.7°C on July 2, #5 35.6°C on July 1, and #8 35.0°C on July 3.

Many of the temperatures this week would have broken daily records during any other week of the year, but they weren't hotter than the 1924 & 1937 heatwaves. And so because of that 2021 ends up with "only" 2 new daily records.

That is just for the daily High temperatures, though. The daily Lows really were unprecedented:

• Possibly 10 overnight Lows in-a-row of 15°C, tying August 1984.
• 9 Lows in-a-row of 17°C, beating 6 from August 2020. (the record before that was 4)
• Possibly 6 Lows in-a-row of 19°C, beating 2 from July 1975
• 3 Lows in-a-row of 20°C. We had never had more than 1 at a time before.

The heatwave set 8 new daily records for overnight Lows. Almost every day from June 25th through July 3rd has a new record, with June 27th as the only day that missed.

2021 has 3 of Edmonton's top-10 warmest Lows ever recorded:

• June 29th is in 8th spot at 20.3°C.
• June 30th set a new record for all-time warmest Low at 22.8°C
• And then the next day July 1st set a new-new record for all-time warmest Low at 23.4°C

So overall, for the High temperatures the Great Heatwave of 2021 was a bit of a combination of previous heatwaves: the super-hot temperatures of June 1924 & 1937, with the long duration of June 1961. For the Lows though, we really hadn't seen anything like it.

Enough words. Now it's time for some charts.

 

Daily Highs

Here we have the High temperatures for the summer of 2021, with the heatwave right in the middle at the end of June. Our average Highs at that point of the year are about 23°C, so the heatwave days were 7~14°C above average. There were a lot of 30°C days packed in there, but only 2 records were broken because the old records were some of Edmonton's hottest days ever recorded.

Daily Lows

Here are the Low temperatures, with all of the new records set during the heatwave. The average Lows at that point of the year are about 12°C, so these records were 5~11°C above average. Earlier in the year there are also some other daily Low records which were broken.

While Edmonton was having its semi~unprecedented heatwave something similar was happening in Calgary and Vancouver. So for a lot of the charts today those cities will be included as well.

30°C Highs In-a-Row

For 30°C Highs in-a-row Vancouver tied its previous 4 day record from 1911. In between those 110 years they also had a 3 day streak in 2009. Edmonton's 7 days in-a-row beat the previous record of 6 days in 1961. Recently we had gone 3 days in 2015 and 2012, and 4 days in 2008 and 2002. Calgary's 7 days did not catch their record of 8 days from 1917, but it did tie for 2nd place with 1896. In recent years they had gone 4 days in 2002 and 5 in 1996.

35°C Highs In-a-Row

For 35°C Highs in-a-row Edmonton tied the 1924 heatwave with 3. And the only other times when we have hit 35°C were 1933 and 1937. Calgary's 3 days beats their previous 2 day streaks in 1919 and 1933.

Hottest Days Ever Recorded

For this heatwave we saw that Edmonton had 3 days in the top-10: #2, #4 and #7. 

Vancouver had its #7 and #8 hottest days, but did not get as hot as its July 2009 heatwave at 34°C. 

And Calgary had 3 days in its top-10: June 29th and July 1st are tied for 2nd hottest day overall at 36.3°C, and June 30th was #6 at 35.9°C.

30°C Highs In-a-Row Around Edmonton

The heatwave didn't just hit the city of Edmonton. For nearby stations the International Airport was at the low end of things with only 5 days in-a-row at 30°C, but most of the other stations had 6 or 7 days. In this chart it's also interesting to see that the 1961 heatwave showed up at several of the stations.

35°C Highs In-a-Row Around Edmonton

Through a lot of this Namao was actually the hotspot, with 4 35°C days in-a-row, including 37.5°C on June 30th. And a little bit further northwest Campsise hit 37.2°C on June 29th and 37.4°C on June 30th.

16°C Lows In-a-Row

Overnight Lows aren't as exciting as Record! Breaking! Highs! but during this heatwave Calgary had 6 nights in-a-row above 16°C, when their previous record was 2. Edmonton set a new record with 9. And Vancouver's 8 Lows was their 2nd most, but was not enough to catch the 10 in 2009.

17°C Lows In-a-Row

For warmer Lows at 17°C all three cities set records. Calgary had 3 in-a-row, when before it had only ever had 1. Vancouver had 7, beating 6 from 2009. And Edmonton has had at least 9, beating 6 from 2020.

19°C Lows In-a-Row

And taking the Lows one step further to 19°C Vancouver had 3 in-a-row, which tied 2009, 1998 and 1941. Edmonton had a new record with 6, beating 2 from 1975.

Edmonton also had 3 Lows in-a-row of 20°C, when previously the most had been 1. Vancouver had 2, but back in 1941 they had 3 in-a-row.

Hottest Nights Ever Recorded

For the overnight Lows in Edmonton 2021 set a new #1 record of 23.4°C, and also has the #2 and #8 spots. Calgary has a 4-way tie for their top spot at 18.3°C, including June 29, 2021. This heatwave also had their #5 and #8 spots. And Vancouver didn't get close to their all-time record of 22.4°C from 2009, but did have the #3 and #4 spots.

Lows Around Edmonton

The overnight Lows for the outlying areas around Edmonton were not as warm as they were in town. But some of the stations had a few very warm nights.

High Temperature Records

In this chart each of the bubbles is a daily High temperature record. This heatwave only set 2 new records for daily High temperatures, and they are over on the right side.

Low Temperature Records

In this chart each of the bubbles is a daily Low temperature record. So far 2021 has set 11 new records, including 8 during this heatwave, and the all-time warmest record Low of 23.8°C on July 1, 2021.

And so that brings us to the end of our lookback at the Great Heatwave of June-July 2021. The Highs were as hot as anything we had seen before, and they were hotter for longer. The Lows were even more unusual, setting all sorts of records and giving us a solid week of unusually hot nights.

If you have some extra time Why Heatwaves Are Not the Whole Story is a good follow up to this look at the heatwave of 2021. This was Edmonton's first really big heatwave in a long time, but there has also been other warming going on in the background too.

June 2021 Review

Today we are taking a look back at a very eventful June 2021.

(if you are reading this in the distant future some of the dashboards below may have updated to reflect new data or formatting, or they may be broken, or they may no longer make sense. To see the original images for this post refer to this twitter thread.) 

As June ends we are still in the middle of a historic heatwave. Obviously we will be talking about that today, but we can't do a real heatwave recap yet because it isn't over. So this post will be about June, and then in a few days we will be back with a giant look at the great heatwave of 2021.

While we are waiting for the heatwave to end, if you are looking for some historic context we did a heatwave pre-cap last week:

• Part 1: Edmonton's Heatwaves
• Part 2: How Edmonton's Heatwaves Compare to other Canadian Cities
• Part 3: Why Heatwaves Aren't the Whole Story

But let's talk about June 2021.

High Temperatures

June 2021 started off warm with a few days at the top of our 30-year range. Then we had a cooler week with a few days just below average, and with June 8th as the coldest at 16°C. Then it was warm, then average, then warm, and then really, really, really warm.

Overall the month had 23 Highs above average and 7 below. That included new daily records of 34.2°C for June 28°C, and 37°C for June 30th, as well as 3 more warmest-in-30-years Highs.

Looking at the numbers we had 24 days with Highs that hit 20°C, compared to an average of about 18 for June. That included:

• 15 days hit 25°C, when June averages about 5.
• 6 days hit 30°C, compared to an average of about 0.5.
• 2 days hit 35°C, with 36.2°C on June 29th and 37°C on June 30th. The last time that Blatchford had any day which hit 35°C was in 1937.

Warm Days So Far

So far the summer of 2021 has had 38 days hit 20°C, which is a little bit more than average for this point of the year. 2020 and 2019 both only had 29, while 2018 was way up at 52, and 2016 had 45.

For 25°C days we have had 15, compared to an average of around 10~12. 2020 was down at 4 and 2019 had 6, while 2018 was way up at 25, and 2015-2018 were all pretty high.

Hot Days Each Year

Here we have the number of 30°C days for the whole year, not just for January-June. So far we have had 6 days hit 30°C: one on June 22nd, and then 5 as part of the end-of-June heatwave. 

The average for an entire year is around 4. Several recent years like 2020, 2019, 2016, 2014, etc. were all low with 1 or 2. But 2018 had 7, 2018 had 6, 2015 had 9, and back in 2002 there were 13. And 1961 has the record with 14.

Super-Hot Days

Since 1880 we have only had 21 days hit 34°C, and 3 of those were in June 2021: June 28th at 34.2°C, June 29th at 36.2°C (our 4th warmest High ever recorded), and June 30th at 37°C.

June 30th came very close to Edmonton's warmest High ever recorded at 37.2°C on June 29th, 1937, but it didn't quite make it. June 29th, 1937 was also the last time that Blatchford had recorded a High of 35°C, for a gap of 84 years to the day. We will talk more about super-hot days in a few days during out heatwave recap.

Low Temperatures

For the Low temperatures June 2021 set 7 daily records. That includes the warmest overnight Low ever recorded, at 22.8°C on June 30th. That broke the previous record of 21.4°C set on July 14, 2007. Even with all of the records there were still 8 Lows below average though, with June 8th as the coldest at 6.9°C.

For the Lows we had 9 nights above 15°C, when June's average is 2. That included 2 nights above 20°C, and recently only June 2002 had another night that warm.

Warm Lows

This chart is normally used to talk about really cold Lows, so it's set up backwards for the summer. But today please pretend that blue means "warm" as we look at Lows of 17°C or more. 

For January-June 2021 we had 6 Lows hit 17°C, while no other January-June has had more than 2.

Really Warm Lows

And here is Edmonton's entire history of 20°C overnight Lows. There have been 11 in total, including 2 in 2021, 2 in 2007, and 2 in 1880. 

Edmonton's very first "modern" temperature reading is from July 11, 1880. Those 2 overnight Lows of 20°C on July 18 and July 22, 1880 are from the 8th and 12th days with records, ever. Because of that it seems like maybe they didn't have the routine down yet, and maybe instead of measuring the coldest temperature at around 7AM, maybe they took the reading a little later in the day. (it was a Sunday and a Thursday).

Warm and Cold Months

And so June 2021's average High of 24.947°C ranks as the #1 warmest June on record, just barely beating out June 1961 at 24.943°C. The average Low of 13°C is also the warmest June on record, easily beating 12.5°C from 1961 and 1970.

June 2020 and 2019 were both below average, but recently 2021, 2018, 2016 and 2015 were all top-15 Highs and top-10 Lows.

June 2021 was still a long way from our warmest month on record though, with July 2007's average High at 26.6°C, and August 1981's at 26.8°C.

June 2021 Across Canada

June 2021 was warm in cities all across Canada. The Highs ranged from 2.5°C warmer than the 20th century average for Vancouver, to 4.2°C for Edmonton, and 4.7°C for Calgary. The Lows weren't quite as warm, ranging from 1.3°C above the 20th century average for Regina to 4.4°C for Edmonton.

Here we have the whole history of June Highs for these cities. 2021 was a top-10 June for every city here with the exception of St. John's in 11th spot.

How Warm is 2021 So Far...?

This chart adds up all of the above and below temperatures for each day of the year. For warm days the line goes up, and for cold days it goes down. At the end of June 2021 the Highs are sitting in the 18th warmest spot, and for the Lows it is 26th warmest. So over all 2021 is about 1.2°C warmer than the 20th century average so far.

The June heatwave shows up with the red line ticking up near the end, but it's not enough to offset the dip from the the 2 week deepfreeze that we had in February. 2021 is still a warm year, but it's well below a really warm year like 2016 which was at 2.4°C warmer than the 20th century average by this point of the year, and ended at 2.9°C.

Looking at 2021 so far across Canada, Edmonton's #18 Highs are right in the middle of the pack. For Winnipeg and Montréal 2021 has been a #4 year so far, while in Calgary it's #26 and in Vancouver it's #28.

Monthly Precipitation

On average June gets 75mm of precipitation, and in 2021 Blatchford only had 24mm, the International had 31.7mm, and Stony Plain had 34.8mm. That's a bottom-10 June for Blatchford going back to 1880, and also bottom-10 for the International and Stony Plain going back to the 1960s.

2021 Precipitation So Far

By the end of June we average about 206mm of preciptation for the year. The International isn't too far off at 164mm, mostly thanks to a rainy May. Stony Plain is quite low at 126mm, and Blatchford is down at 109mm. For Blatchford that is another bottom-10 since 1880.

This chart is always a little messy, but it has the cumulative precipitation for 9 cities across Canada. Edmonton's 109mm is right at the bottom, although Calgary and Winnipeg are both down there with bottom-10 years as well. St. John's is at the top with 699mm, which is pretty average for St. John's.

July Temperatures

And what might we expect for July? July's average High is about 23.5°C, which is a little bit cooler than the record-breaking June which we just had. On average July has about 25 days which hit 20°C, including about 10 at 25°C. Most July's will get at least one 30°C day, but recently 2020, 2019 and 2016 didn't. The Lows are usually very boring, with almost all of them falling between 10-15°C, and the rest either a little warmer or a little cooler. July is also usually our rainest month, with an average of 90mm.