Deepfreeze 2019!

The great deepfreeze of 2019 ended on February 18th. Things were still cold after that, but that was the end of the official streak, so let's see how it compared to the deepfreezes of the past century.

Today is a bit of a long-gap sequel to two posts from a few years ago:

• Coldsnaps & Deepfreezes
• It was the winter of '69

In those posts we looked at recent deepfreezes, and also at Edmonton's very longest deepfreezes. Today we will be covering some of that again, but this time we have a few new charts to play with which should show how often these occur.


The Lows

The winter of 2018-2019 had been fairly mild...but then February happened. And February wasn't just "typically" cold - the first 18 days were right at the very bottom of the range of temperatures that we've seen in recent years, including 10 days with coldest-since-1996 temperatures. That was still typically about 10°C warmer than the coldest-since-1880 records, though.

In those first 18 days we had 3 days which hit -30°C, while in the past 20 years we had only had 2 other -30°C February days (in 2018 and 2008).

We had 14 Lows which hit -25°C, compared to the coldest recent February in 2014 which only had 6.

And we had 18 Lows hit -20°C, when recent cold February's had topped-out at 12 in 2018, 13 in 2014, and 15 in 2011.


Recent Coldsnaps

For recent winters going back to 2010-2011 the longest stretch of -25°C Lows that we had had was 5, and that was last winter. This year we went 9 days straight, took one day off, and then had another 4 day stretch.

For Lows of -20°C both 2010-2011 & 2017-2018 had stretches of 9 in-a-row. This winter we doubled that with 18 Lows of -20°C or colder in-a-row.

So we haven't seen anything like this is "recent" memory.

At the end of January this winter had been mostly deepfreeze-free. But February fit an entire winter's worth of -20°C and -25°C days into just a few weeks.


Lows of -25°C or Below: 9 in-a-row

The stretch of Lows of -25°C or colder ended on February 10th, after 9 days in-a-row. That was not the end of the -25°C Lows, which only took one day off and then returned for another 4 day stretch.

9 in-a-row is Edmonton's 39th longest stretch of -25°C Lows since 1880, and the longest since 12 days in January & February 1996. And before that we need to go back to 14 days in 1984.

Edmonton's longest recorded stretch of -25°C Lows was the infamous January of 1969, with 26 in-a-row.


Lows of -20°C or Below: 18 in-a-row

For Lows of -20°C or below we went 18 in-a-row, which made it Blatchford's 22th longest streak.

The last time that we had a streak this long was back in the mid-1990s, with 23 Lows of -20°C in-a-row in 1996, and also 17 days in 1993. In the last 20 years we had had one 10 day streak in 2003, and everything else had ended at 9 days. So this was twice as long as the longest coldsnaps that we have seen recently.

Edmonton's longest recorded stretch of -20°C Lows was 46 (46!) spanning from December 1949 into January 1950.

This chart shows how the number of long deepfreezes has changed over time.

To make this make sense there's a bit of cheating going on: on the various slides of this chart a 15-day deepfreeze is counted as 3 x 5-day deepfreezes, 2 x 6-day deepfreezes, 2 x 7-day deepfreezes, 1 x 8-day, and etc. Without that it would be counting the really, really long deepfreezes as 1, and that isn't fair.

One thing to notice from this chart is how much more rare 10+ days deepfreezes have been since the mid-1990s. From 1980-1996 there were 10 10-day streaks, and since there there have only been 2 in 2019 and 2003.

Calgary

Calgary also had its own generational deepfreeze, with 14 -20°C Lows in a row. That made it Calgary's 27th longest streak, and the longest since 18 days in 1996. Calgary's record is 31 days from 1965.


The International Airport

In the past we have talked about how much colder the Edmonton International gets than Blatchford, most notably in The Edmonton International Airport: Part 2. Typically during the winter the airport's Lows will average about 3°C below Blatchford, but on really cold days it gets a lot colder. And that happened again during this deepfreeze.

Blatchford had 3 -30°C Lows, while the International had 10. And those 10 days included 5 which were -35°C or colder with one -41.2°C on February 5th.

During this deepfreeze the biggest gap between Blatchford and the International was 10°C on February 4th, with Blatchford at -29.5°C while the International was down at -39.5°C. And there were 10 days where the International's Low was at least 5°C colder than Blatchford.


The Highs

The High temperatures weren't quite as exciting as the Lows, but we set 9 coldest-since-1996 Highs.

Highs of -15°C or Below: 11 in a row

On February 13th we hit a balmy High of 14.3°C, which ended our run of Highs of -15°C or below at 11 days. That was the 31st longest streak since 1880, and the longest since a 15 day streak in 1998. And before that we need to go back to 1982 for a 17 day streak.

Edmonton's longest run of Highs of -15°C or below was 28 days in January 1934.


Highs of -10°C or Below: 18 in a row

And one more streak: we had 18 days in-a-row with Highs of -10°C or below. 18 days at -10°C doesn't seem all that impressive, but it was actually Edmonton's 15th longest stretch.

This was the longest since 23 days in 1996, and Edmonton's longest recorded stretch of -10°C Highs was January 1950 again.

So that about covers the actual deepfreeze days, but the rest of February 2019 was pretty cold too. We will look at that in the February review at the end of the month.