Freeze/Thaw Cycles: Part 2 - Versus Round

Last week in Free/Thaw Cycles: Part 1 we looked at how the number of freeze/thaw cycles in Edmonton each year has changed over time. Today we are going to expand that to look at a few of Canada's other winter cities.

The weather stations which we will be comparing today are:

• Edmonton Blatchford (2km from downtown)
• Edmonton International Airport (25km from downtown)
• Calgary International Airport (9km from downtown)
• Winnipeg International Airport (6km from downtown)
• Montreal Airport (13km from downtown)

Each time that we look at the data from these other cities it is with the caveat that the data is not necessarily 100% equivalent because of where the stations are located. But these stations are the ones with a long history of data, and so they might not be perfect but they are what we have available.

Also, counting freeze/thaw cycles is a little bit complicated, and the methodology which we used was explained in Freeze/Thaw Cycles: Appendix.


And now, let's go:

Freeze/Thaw Cycles Each Year

Here we have the freeze/thaw cycles each year for each of the stations. The 5-year averages are included as dotted lines to get rid of some of the noise from the yearly numbers.

• Blatchford averages about 90 freeze/thaw cycles, which has been consistent since about the 1930s. Before that it was up around 110.
• The Edmonton International in recent years has had around 120~125 freeze/thaw cycles each year, which is up from the 110 which it used to get in the 1960s.
• Calgary has averaged about 125 freeze/thaw cycles going back to around the 1940s. Before that it was up at around 140.
• Winnipeg has hovered around 75 freeze/thaw cycles for the last century. Sometimes it is a bit below, and right now it is a bit above.
• Montreal used to be at around 60 freeze/thaw cycles but right now is at around 70.

It is not surprising to see that Calgary has more freeze/thaw cycles than Edmonton, but so does the Edmonton International? And for the last 10 years the Edmonton International has almost been tied with Calgary? And obviously Winnipeg has fewer freeze/thaw cycles than Calgary or Edmonton, but Montreal is down there too for some reason? What's going on?


Freeze/Thaw Cycles Each Month

Here we have the average number of freeze/thaw cycles each month for these stations, for 2000-2018.

• Blatchford is middle-of-the-pack for most of the year. But in the shoulder-season months - April, May, October - it's the 2nd lowest, above only Montreal. 
• The Edmonton International is middle-of-the-pack during the winter - December, January & February. But for the rest of the year it's very high, especially in April, September & October.
• Calgary is highest in the deep-winter months of November through March. It is middle-of-the-pack during the shoulder-season months.
• Winnipeg is the lowest by far during December-March. It's fairly high for April-June.
• Montreal is the lowest by far during the shoulder-season months of April, May, September & October. For December it is a little above Edmonton, and for January & February it is below.

For the yearly counts of freeze/thaw cycles we saw that Calgary and the Edmonton International had similar totals. Here can see that even though the yearly numbers are similar, they are coming from very different places. Calgary's "extra" freeze/thaw cycles are in the deep-winter, while the Edmonton International's are in the late-spring and early-autumn.

We also saw that the yearly totals for Winnipeg and Montreal were both quite low. Compared to the other cities Winnipeg is "missing" freeze/thaw cycles during the deep-winter, while for Montreal it is the spring & autumn which are very low.


Thawing Days & Freezing Nights Each Month

Here were are comparing the freeze/thaw cycles for the stations again, but this time we have added the number of Highs Above Freezing in red, and the Lows Below Freezing in blue.

In Part 1 we saw that there are different drivers for freeze/thaw cycles depending on where we are in the year. In the winter warm days are relatively rare, and so a freeze/thaw doesn't happen unless there is a warm day. On the other hand, in the spring & autumn most days are above freezing, and so a freeze/thaw doesn't happen without a cold night.

In the animated version of this chart there is a lot of stuff going on, so let's take a look at each station individually.

Blatchford

Blatchford is pretty middle-of-the-pack across the board. Its Highs Above Freezing are pretty high in January & February, but they are still below Calgary. And its Lows Below Freezing are pretty low in April, May & October, but they are still above Montreal.

Edmonton International Airport

For the Edmonton International the story is that it gets a lot of Lows Below Freezing in April, May, September & October. Its Highs Above Freezing are middle-of-the pack and a close match to Blatchford, but all of the freezing nights during the shoulder-season months are what sets it apart.

Calgary International

For Calgary it is not a surprise that there are a lot of mid-winter Highs Above Freezing. For December-February it averages about 5-7 per month more than Edmonton, 7-10 more than Montreal, and 12-15 more than Winnipeg. It's Lows Below Freezing are in the middle-of-the-pack for most of the year.


Winnipeg International

For Winnipeg the story is the lack of Highs Above Freezing during the winter, with 5~10 fewer each month for December-March than the other cities. Its Lows Below Freezing are also high from January-May, but are middle-of-the-pack for September-December.


Montreal

For Montreal the number of Lows Below Freezing is the lowest of all of the stations for almost the entire year. And its Highs above Freezing are the highest for March-November, while being a little low for December-February.


Freeze/Thaw Cycles Each Year, Again

And so here we are back where we started, with the number of freeze/thaw cycles each year for each of the stations. But this time we have also added the number of Highs above freezing in red, and the Lows below freezing in blue.

The animated version of this chart is also pretty busy, so we will break the stations out separately again.


Blatchford

For Blatchford:

• the yearly Highs above Freezing are in the middle of the pack
• the Lows below Freezing have fallen to the bottom of the prairie stations, but with about 175 per year they are still well above Montreal's 145ish.
• as we saw at the start today, the freeze/thaw cycles are in the middle.

 Edmonton International Airport

For the Edmonton International:

• the Highs above Freezing are in the middle of the pack
• the Lows below Freezing are the highest for all of these stations.

 Calgary International

For Calgary:

• the Highs above Freezing are the highest for all of the stations, and have stayed fairly constant at around 300 over the past century.
• the Lows below Freezing are in the middle of the pack, and have fallen from an average of about 200 a century ago to around 175 today.
• as we saw at the start today, the freeze/thaw cycles have decreased from about 140 to around 125 today.

Winnipeg International

For Winnipeg:

• the Highs above Freezing are the the lowest for all of the stations, and have stayed fairly constant at around 250 over the past century.
• the Lows below Freezing are in the middle of the pack, and have stayed at around 185 for the past century.
• the freeze/thaw cycles have stayed constant at around 75.

Montreal

For finally, for Montreal:

• the Highs above Freezing are above Edmonton but below Calgary, and have increased from about 275 a century ago to just under 300 today.
• the Lows below Freezing are the very bottom, and well below these other stations. Montreal has about 150, compared to 175-200 for the others.
• and with that the freeze/thaw cycles have increased from an average of about 60 a century ago to about 70 today.

Summary

As we saw last week in Part 1, freeze/thaw cycles have always been a part of Canadian winters. And to have a freeze/thaw cycle you need both a freeze and a thaw.

• Calgary gets a lot of freeze/thaw cycles because it has a lot of mid-winter thaws.
• The Edmonton International also has a lot of freeze/thaw cycles, but that's because of its many shoulder-season freezes (and it also has a reasonably high number of mid-winter melts).
• Winnipeg's freeze/thaw cycles are low because it has very few mid-winter melts - 1/4 as many as Calgary, or 1/3 as many as Edmonton.
• Montreal's freeze/thaw cycles are low because it doesn't have many shoulder-season freezes.