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.
- 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.
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.
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.
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.
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.
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