Record Watch: August 30

It's supposed to be pretty warm today, with a forecast High of 31°C.

The warmest-recorded overnight Low for August 30 was in 1971 at 16.7°C. And looking at Environment Canada's number for today, we've already dipped a bit below that hitting 15.6°C at 6AM.

The warmest-recorded High was set in 1940 at 32.2°C. And since 1880 we've only broken 30°C on other time on August 30, in 1967 at 30.6°C. 

Since 2000 we've only broken 25°C three other times - in 2007, 2009 and 2015 - and we also had two years which didn't break 15°C - in 2006 and 2010.

A fun chart

Nothing too profound today. A few weeks ago the New York Times had a fun animation showing how summer temperatures in the Western Hemisphere have changed over the last half-century. I can't find a way to embed the animation, but the story is worth a read, and here's one screenshot:

Source: New York Times, July 28 2017, It’s Not Your Imagination. Summers Are Getting Hotter.
By NADJA POPOVICH and ADAM PEARCE

The chart and data come from Dr. James Hansen, and the background behind it be found here:
Global Temperature in 2015

I was curious what something similar would look like for Edmonton, so here is my version:

This shows roughly how the High temperatures in Edmonton are distributed for June through August. This chart is smoothed a bit

Since the 1950s things have been pretty consistent:

• about one-third of summertime Highs are below 20°C
• 40-44% of the time the Highs are from 20°C to 25°C
• 20-25% of the time the Highs are from 25°C to 30°C is 
• and about 4% of the time we break 30°C (3 to 4 days each summer)

In the last ten years the most notable change was that the number of Highs below 20°C was lower than normal, at 27%. So that shifts the 2007-2016 distribution to the right a bit compared to all the others. But honestly, it's not as dramatic as I would have hoped.

If we switch from decades to individual years things move around a bit more:

Yearly Comparison

This give a sense of the variety of summers over the last decade.

Both 2010 and 2011 were pretty cool, with less than 20% of the Highs above 25°C. More typically it's somewhere around 30%. And the summer of 2015 was above 25°C for 47% of the time.

For the Highs below 20°C, in 2015 it was 14% of the summer, and in 2016 it was only 12%. That's well below the 30-35% which is more typical. For some context, since we're looking at the 92 days from June-August, that means a difference of 20% is equivalent to about 18 days.

These charts are fun, although I think it's actually a little difficult to spot trends or make good comparisons from them. For that, I still prefer this type:

We've looked at this chart before here, and it's a comparison of the temperatures for the entire year, rather than just for the summer.

In a couple weeks we'll check in on 2017 to see how it compares so far.

July Review / August Preview

High Temperatures

We've talked before about how July temperatures in Edmonton fall in a fairly narrow band, and we saw that this year with a spread of about 15°C between the coldest and warmest days.

The coldest day last month was July 24 at 15.1°C. That was the second-coldest July 24 High ever recorded in Edmonton, with the all-time coldest being 13.3°C in 1953. For the sake of trivia, in the recorded history of temperatures in Edmonton there have only been 4 July days which didn't break 10°C: July 3 1884 at 7.8°C, July 8 1885 at 8.3°C, July 14 1913 at 9.4°C, and closer to home July 31 2002 at 9°C.

The warmest day this month was July 7th at 30.3°C, which was a recent record, but was still a few degrees below the all-time record of 32.2°C set in both 1894 and 1960.

This chart also highlights how many recent days have been above or below average, and in the last two months the highs have been pretty consistently above average. Looking at August and September we can see that the average Highs stay pretty level for the next month, before starting to dip right at the beginning of September.

Taking a closer look at the numbers, this July we had 4 days above 30°C and 17 above 25°C. That was the same as in 2015, but was quite a few more than we had last July.

Our average High temperature was 25.1°C which is on the warm side of things, but is below the very warm July's of 2006 and 2007, and is actually tied with July 1917 from a century ago.

Low Temperatures

For the Low temperatures we didn't set any all-time or recent records this month, and were split between above and below average.



These charts can be daunting, because there are just so many numbers. But the easiest thing is to just look at the colours - and for July Lows almost everything is the same 10-20°C orange. The lighter-orange shows the night below 10°C, and we had 4 of those last month. The darker-orange is the nights where temperatures stayed above 20°C, and the last time we recorded any of those was in 2007.

Precipitation

If I had needed to guess how much precipitation we had this July, I would have said that it was pretty low. And that guess is partly accurate, and partly not.

At the International Airport the amount of precipitation this July was right on the average with 90mm, but in the city Blatchford recorded barely half that amount at 49mm. Normally the International and Blatchford are pretty close, so I use the International since its data is better. But last month the gap was so large that it is definitely worth mentioning. Looking at the year so far, Blatchford has record 268mm of precipitation compared to 335mm at the International.

This chart also shows the International's 2016 precipitation as a comparison, and 2017 has had a drier summer after a wetter spring.



This chart shows the total, cumulative precipitation so far for 2017 at the International. With 335mm we're getting close to the 350mm-mark, and are sitting right around the 75th percentile.

August Temperatures

As we move into August we can expect that most of the daytime highs will still be above 20°C, and we'll get a week or two above 25°C. 30°C days are a little rare though, and about half of the time August won't have any.

For the Low temperatures it should be a lot of the same 10-20°C orange which we saw for July, but with a few more nights in the 5-10°C range, and every 5 years-or-so a night below 5°C.