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2017/01/06

It was the winter of '69

According to the weather forecasts tomorrow will be the start of a deepfreeze.

Tomorrow also marks the 48-year anniversary of Edmonton's historic deepfreeze, which started on January 7th, 1969, and which lasted all the way to February 1st. By the end of it Edmonton Blatchford had recorded 26 straight days where the daytime high temperature did not break -21°C.

It was such a big deal that the Edmonton Journal printed this certificate:

Source: Photobucket
The temperatures in that certificate are all in Fahrenheit, and so -6F is equal to -21.1°C, and -39F is 39.4°C.

Today we're going to take a closer look at the 1969 coldsnap, but for some context first we're going to start with recent history:



In the background of this chart we have "typical" temperatures for the last 20 years - the average, quartiles, and maximum & minimum temperatures since 1996. There's also a line for the daytime high temperatures from the winter of 2015-2016, with highs that were above freezing in orange, and highs below freezing in blue.

And now lets look at 1969:

The 1969 Coldsnap

Here 1969 is shown as the dashed, grey line, and its historic coldsnap is highlighted in dark blue.

We know that 2015-2016 was a pretty mild, El NiƱo winter - there wasn't a single high below -20°C. And we can see that for almost the whole winter 1968-1969 was at least 5°C or 10°C colder than last year was. And if we just focus on the coldsnap, those 26 days were all basically as cold or colder than anything we've seen in the last 20 years.

Right before the 1969 coldsnap started the temperature had been very warm at just above 5°C, so they probably had no idea what they were in for. And once it was all over, after almost a month below -20°C the temperature jumped straight up to 0°C, which must have felt amazing.

Was the 1969 coldsnap truly unusual, or has a bit of "walking uphills both ways" crept into this story?

Other -20°C Coldsnaps

Here are the next-longest coldsnaps below -20°C, and none of them come close to January 1969. The 1969 coldsnap lasted 26 days, and going all the way back to the 1880s its closest competitors were 16  days in December 1933; 16 days in January 1954; and 17 days in February 1936.

Other 25-day Coldsnaps

If instead we go looking for other 25-day-streaks, we have to warm things all the way up to -16°C. And when we do that, December 1933 and February 1936 show up again.

So January 1969 really was pretty unique in Edmonton's history.

It's worth mentioning that this deepfreeze wasn't limited to Edmonton:

Calgary

Here we have Calgary's high temperatures during Edmonton's coldsnap.

Calgary had a deepfreeze too, but it started one day later, ended two days earlier, and in the middle it popped up to -16°C for one day. It's not quite as headline-ready as "26 days below -6F!" but Calgary still had 22-of-23 days below -4F.

Low Temperatures

Today we've just looked at daytime highs, but to finish things off I've added the daytime lows for the January 1969 deepfreeze.

That stretch also included 26 straight low temperatures below -25°C, which was another record - the next closest was 19 days below -25°C in 1934. And during the 1969 coldsnap there were 18 lows below -30°C, and 7 lows below -35°C.

For a bit more trivia, here are a few of Edmonton's other low temperature streaks:
  • lows below -30°C: 16 days from January 28 through February 12, 1887
  • lows below -35°C: 11 straight days in that same stretch of January 28 through February 7, 1887
  • lows below -40°C: 7 days, from January 28 through February 3, 1893
Today we've looked at historic deepgreezes, and depending on just how long this next deepfreeze lasts, in a week or two we'll take a look at some recent coldsnaps.

Update:

Here is one more look at the winter of 1969, showing the Highs & Lows for December through March.

The historic deepfreeze in January was 26 days, but the Lows actually dropped below -20°C quite a bit earlier. From December 22 to February 2 41-of-43 Low temperatures were below -20°C, with only a two day warmup to -10°C and -15°C on January 4th and 5th.

And for some context, here are the deepfreezes from the last few years:

Since 2010-2011 the most Highs below -20°C that we've in an entire winter was 12 days, and the longest stretch was 5 days in a row. Most of our Highs below -20°C have only lasted 1-3 days.

For Lows below -25°C the most that we had in these winters was 17 days, and the longest stretch was 5 days.



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