Heat Wave June 2021: Victoria breaks its all-time high temperature record

The heat wave that Victoria and the surrounding region just experienced was truly historic.  Weather historian Christopher Burt described it as “the most anomalous regional extreme heat event to occur anywhere on Earth since temperature records began" roughly 150 years ago with the beginnings of modern meteorology.  Never before have so many all-time temperature records been broken by such a large margin in one region by a single event.  According to international weather records researcher Maximiliano Herrera, more all-time heat records were broken by at least 5 C in the June 2021 heat wave than in the previous 84-plus years of world weather recordkeeping.  A group of international climatologists estimated that this heat wave was a 1 in 1,000 year event for our region, and that even with continued climate change, it will remain a very rare event.

On June 28, 2021, Victoria recorded its all-time maximum temperature: 39.8 C.  That completely shattered the old record of 36.0 C set on July 11, 2007.  Many other locations in B.C., Washington, and Oregon also broke new all-time maximum temperature records.

Below are the June 25-29 daily high temperatures around the Victoria region:

The numbers are extraordinary.  Most locations broke their all-time temperature record on June 27, then broke it again on June 28.  Typically, when an all-time temperature record is broken, it might be by a fraction of a degree.  In this case, Victoria Gonzales beat its old record by 3.8 degrees, while Victoria Airport beat its old record by 3.1 degrees.  

The chart below shows hourly temperatures at Victoria Gonzales during the heat wave, compared with the average daily maximum and minimum temperatures in late June.  The peak temperature of 39.8 C at about 3 pm on June 28th was nearly 20 degrees C above the average!  Even the overnight lows on June 26th and 27th were higher than the average daily maximums.  

Some specific patterns are notable:

On June 26th, an on-shore sea breeze developed in the late morning and early afternoon that prevented temperatures at Gonzales from getting really hot.  The temperature peaked at 32.5 C between 11 am and noon, but then plunged to 23.4 C by 1 pm as the sea breeze kicked in.  

A sea breeze also developed on June 27th, but much later in the day.  The temperature peaked at 38.3 C between 2 pm and 3 pm.  It was still 35.9 C at 6 pm, but then a sea breeze developed and the temperature plunged 10 degrees in an hour, to reach 26.2 C at 7 pm.

The late evening, overnight, and early morning period between June 27th and 28th was remarkably warm.  After the early evening sea breeze on June 27th, the temperature warmed again, and was still a remarkable 28 C at midnight.  For most of the night, the temperature remained above 24-25 C, with just one hourly recording at 4 am  when the temperature dropped to 22.1 C.  By 7 am, the temperature was back up to an amazing 29 C, and it continued to increase sharply from there.

Also of note is the dramatic fall in temperatures on the evening of June 28th.  After hitting its peak of 39.8 C around 3 pm, the temperature remained a very hot 37.4 C at 6 pm, but then fell to 15.6 C at 6 am on June 29th - a drop of nearly 22 degrees C in 12 hours.  By the morning of June 29th, the heat wave was a distant memory, with a 10 am temperature of 16.2 C compared with 34.8 C at 10 am on June 28th.  That's a remarkable 18.6 degree C temperature change in 24 hours!  

In addition to these official Environment Canada weather stations, victoriaweather.ca (operated by University of Victoria climatologists) has a more extensive network of weather stations in the region.  Roughly 20 of these sites topped 40 C on June 28.  The table below shows the hottest of these in each municipality:

The chart below shows the annual maximum temperature at Victoria Gonzales over the past 120 years. The new record maximum set this year clearly stands out!

This next chart looks at the peak temperature for just the 10 hottest heat waves ever recorded at Victoria Gonzales:

Again, the June 2021 heat wave clearly stands out as something extraordinary.  All the previous heat records were in a fairly narrow band between 33 C and 36 C, while the extreme heat we just experienced was nearly 4 degrees higher!

As a result of the heat wave, June 2021 ended up being the warmest June on record at Victoria Gonzales.  If you look at the period from June 1 to June 24, prior to the heat wave, the mean temperature was 14.8 C, which was warmer than the 30-year average of 14.3 C, but not unusually so - the mean temperature for June 1-24 was warmer in 10 of the previous 30 years.  However, the heat wave bumped up the mean monthly temperature for June 2021 to 16.6 C.  That's 0.5 degrees warmer than the previous warmest June, when it averaged 16.1 C in 2015.  

So what caused this extraordinary event?  It was the result of an unusually large wave in the jet stream, which may have been caused by a tropical system interacting with the jet stream in the eastern Pacific. This created a strong upper-level high pressure ridge over the BC Interior, which results in sinking air and warm temperatures.

Victoria gets this situation fairly often during the summer, although this was already an unusually strong ridge – one of the strongest ever measured. The heat was then amplified by a low pressure trough approaching the coast at just the right time and location to maximize this event. The pressure differential created a strong southeasterly flow from the Interior out to the coast. The warm air from the Interior was heated even more as it crossed the Coast Mountains and compressed as it descended towards the coast (this is a phenomena like the hot Santa Ana winds in Southern California).

On a typical hot day in Victoria, rising warm air over the land draws in cool air from the Strait of Juan de Fuca, resulting in a cooling sea breeze – especially for areas near the Strait like Esquimalt, James Bay and Fairfield. Victoria Gonzales, being so close to the Strait, is often one of the cooler spots in the region on hot summer days, several degrees cooler than areas further inland. In this case, the strong northerly breeze that resulted from the flow of hot air from the Interior blocked the sea breeze from developing. As a result, Gonzales, with a maximum temperature of 39.8 C on June 28, was the hottest of all the Environment Canada recording sites in the region.

Another factor may have been the time of year when this happened. Many people seemed surprised about how early in the summer this heat wave occurred, given that we usually get our warmest average temperatures in late July or early August. However, if you look at the top 10 hottest days ever recorded in Victoria, 6 of them occurred between June 25 and July 1. It may be that the very long days and strong sun this time of year (close to the summer solstice) contributes to these heat waves.

So the unprecedented heat was the result of all these factors combining in just the right way to create the “perfect” extreme heat situation. This combination of events is unlikely to be repeated any time soon.

Given the extraordinary and historical nature of this heat wave, it is worthwhile looking at some of the other temperatures recorded elsewhere in B.C., Washington, and Oregon.

First, some maximum temperatures for the rest of Vancouver Island, with several locations topping 40 degrees C.  Port Alberni, as is typical, recorded the highest temperature on the Island, with 42.7 C.

Next, several locations in Metro Vancouver, the Fraser Valley, Howe Sound, and Sunshine Coast.  Vancouver Harbour, right near the water and with westerly breezes, was one of the "cooler" spots at 33.8 C.  However, several locations in Metro Vancouver were at or above 40 C.  Temperatures were even hotter - around 43 C - in Abbotsford, Squamish, and Whistler.  

Both Seattle (42.2 C) and Portland (46.7 C) broke all-time maximum records.

Finally, in the B.C. Interior, several locations reached or exceeded the old Canada-wide all-time maximum record of 45.0 set in Middale and Yellow Grass, SK in 1937.  This included Lytton reaching an amazing 49.6 C to set a new Canadian national temperature record, and the record for the highest temperature ever recorded north of 45 degrees N.