April Review / May Preview

It's the end of the month, so it's time to look back at a weird April.

A caveat for today: Environment Canada's daily data for Blatchford is missing from April 21st onwards. They still have the hourly data, and that is generally fine, but it doesn't capture the very highest or lowest temperature each day, so it isn't great for things like records. This isn't ideal, but we'll make do.

High Temperatures

April started out really cold, as the late-March coldsnap dragged on for two extra weeks.

We actually set a record for all-time coldest High on April 5th at -8.8°C, and we also set 3 other recent (since 1996) coldest Highs on April 6th, 11th and 12th. And then at the end of the month we set a recent record for warmest High on April 28th at 27.5°C, which was still about 2°C below the all-time record of 29.4°C from 1939.

What a weird month.

The average High was 7.4°C, which was just a bit below the 7.6°C from last year. But we got there by having 9 Highs below 0°C (which tied 2002) including 3 Highs below -5°C (which tied 2008). And then in the last week of the month we had 3 Highs above 20°C (which is pretty high), including 27.5°C on April 28th, which was Edmonton's warmest April day since April 16th, 1984 at 28.1°C.

Low Temperatures

The Low temperatures were similar to what we saw for the Highs, with 3 recent coldest-Lows in the first week of the month. And then at the end of the month the 7.1°C Low on April 28th was just a touch below the recent record of 7.2°C for that date.

Looking at the numbers this April had more Lows below -15°C and below -10°C than any other recent April. The average Low of -3.3°C was the third coldest of these years, behind 2013 at -3.5°C and 2002 at -5°C.

2018 Temperatures So Far...

Before the late-April heatwave people were getting pretty grumpy with our forever-winter. But how does 2018 rank, so far?

This chart compares temperatures on a day-by-day basis to the 20th century average. 2018 is shown as the animated red line, and lines for the last 10 years are shown for reference.

At the beginning of March, 2018 was above the 20th century average, but that still grouped it with the colder recent years - 2009, 2013, 2014. Then the March/April coldsnap dropped us below the 20th century average, and now the late-April heatwave has moved to just below the 20th century average again.

On a month-by-month basis this is how things have broken down:

Looking back at the past winter:

  • December was warmer than the 20th century average, and it was about 1°C warmer than the recent 5-year average.
  • January was also warmer than the 20th century average, but it was still about 1°C cooler than recent years.
  • All the other months have been colder than both the 20th century average and the recent average.

So yeah, back in the 2017-2018 Winter in Review - Temperatures we saw that 2017-2018 wasn't that bad. But it's definitely been cooler than what we're used to.

Monthly Snowfall

Here we have the monthly snowfall at the International Airport, for both this winter and last winter.

This April we got 12cm of snow, most of which was during a big 10.4cm snowfall on April 16th. That's just a bit below average, and it's well below last year's record 43cm of snow in April 2017.

There's still about a 50/50 chance of snow in May, but so far this winter:

  • September, October and March were well above average.
  • December was well below average.
  • November, January, February and April were all in the typical range.

Cumulative Snowfall

When we add the total snowfall up for the year right now we are at 116.9cm. That's below the 136.7cm from last winter, and below the Airport's average of about 125cm. But again, half of the time we'll get snow in May, with an average of 6cm.


Here is our snowdepth for this winter:

  • The International and Blatchford were both high in November
  • They were both a little low in December and most of January
  • At the end of January things took off, and we stayed pretty high through the end of March
  • And then with our cold April the snow refused to melt. For a few weeks we were actually above any other recent years, even though this wasn't a particularly snowy year.

This winter the melt started in earnest on April 8th when the International was at 31cm of snow. By April 21st it had dropped to "trace" amounts, and then to 0cm by April 23rd. That put it ahead of 2013 and 2011 which first reached 0cm on April 27th and 29th respectively, but behind every other recent year.

May Temperatures

And finally, here is a quick preview of what temperatures might look like in May.

May hasn't had a High below freezing since 1959, so that's nice. But about one third of the time we'll have a few days that stay below 5°C. On the other side of things we should probably see a week or two of days above 20°C (2000 was the only real under-achiever, with 2 20°C days). 2015, 2016 and 2017 all had almost a week of 25°C days, and 2013, 2016 and 2017 each had a High of 30°C.

For Low temperatures, about a quarter of the time May will have no lows below 0°C, although more typically there are a a handful. If you are interested in when the final frost is likely to fall, we just looked at that last week.


Record Watch: April 28

Right now the forecast for April 28th is a scorching 27°C. Does that put us into record territory?

April 28th Temperatures

The record High temperature for April 28th is 29.4°C, set in 1939. So to beat the we would need to be well above the forecast.

If we do hit 27°C though, that would be enough for 3rd-warmest, below 1980 at 28.4°C but above 1926 which is currently in 3rd at 26.7°C.

Warmest Temperatures for This Week in History

Here we have the 50 warmest temperatures for the last week of April. The records for this week range from 27.8°C for April 30th up to 31.1°C for April 29th. And three of those records - April 24, 25 & 26 - were all set during a 1977 heatwave.

To make it into this top-50 list requires a temperature of 23.9°C, so April 27th might be included - right now we need to wait for the official results. Recently there are almost no days in this top-50, with only April 27th 2001, and April 28 2010 making the cut. Going further back though, the 1930s and 1940s each had 8 days in the list.

Recent Aprils

That's not to say that we haven't had any warm April days recently. In this list there are 3 days above 25°C which appear in red, and another 17 that were above 20°C in orange. Those warm days just occurred earlier in April, or they weren't quite warm enough to crack the top-50. But this year we might get 2 days into the list.


Frost-Free Days: Part 1

Today we are going to take a look at Edmonton's frost-free days, and at how they've changed over time.

I am not a gardener, and the biggest clue that I am not a gardener is the fact that it has taken more than 2 years for this blog to get around to the subject of frost-free days. They're clearly an important part of Edmonton weather, but they're also totally in my blindspot. We're going to try to fix that oversight today, but with the warning that because I don't garden I don't necessarily know how all this stuff works.

Last Frosts Each Spring

We're going to start by looking at the last frosts that occur every spring.

"Firsts" and "Lasts" of anything are always a bit variable, and so this chart shows the last 5 frosts for each year, going back to 1881. The number 5 has no special significance, but there are some years with a really late, outlier frost and this gives a sense of how big the gap is between those and the rest of winter.

The typical measurement used for frost-free days is 30-Year Averages, and the orange lines in this chart show how that has changed over time.
  • At Blatchford right now the average date for the final frost is May 7th, but a century ago it was almost 3 weeks later on May 27th. 
  • The 2nd frost is on-average 5 days before the last frost, and is on May 2nd. A a century ago that gap averaged 10 days. 
  • April 24th is the average date of our 5th-last frost, which is about 2 weeks before the final frost. A century ago the average date of the 5th-last frost was May 7th, and that lines up with where our final frosts are today.

One thing to keep in mind with these averages is that they only mark the midpoint - half of the time the last frost will occur before the average, but the other half of the time it will occur after. Looking at some recent years, 2012 had one of the earlier final-frosts on April 18th. On the other hand, in this chart for both 2009 and 2004 we can see that the dark-blue lines cross the average, and that's because 2009 had 6 frosts after May 7th and 2004 had 5.

For a bit more trivia, the year with the biggest gap between that 2nd-last and the last frosts was 1915, with 33 days between a frost on May 12 and the final frost on June 14. Looking at more recent years:  1997 had a gap of 21 days from April 30th to the final frost on May 21th; and 2000 went 19 days from April 18th to May 7th.

We'll talk a bit about the probability of avoiding an extra-late last frost later on.

First Frosts Each Fall

Moving to the other end of the summer, this chart shows the first 5 frosts for each fall.

Looking at the 30-Year averages again:
  • Right now the average date for the first frost each fall is September 24th. That's 18 days later than the September 6th date from a century ago. That shift is also similar to the 20 days that we saw when we looked at the last frost for each spring.
  • On average the 2nd frost occurs 5 days after the first, and then by October 10th we've averaged 5 frosts. Both of those dates have also shifted by about 20 days over the last century.

In this chart 1992 stands out with a really early frost on August 22nd, and it actually had a total of 7 frosts before the average date. To find another year with a frost that was before September we need to go all the way back to 1934. On the other end of things 2011 was a really late year, with the first frost waiting until October 15th. The latest first frost was in 1975, on October 21st.

Frost-Free Days

When we combine the last spring frosts with the first fall frosts this is where we end up for the year.
(for clarity there's the fancy, animated chart, as well as a non-fancy version)

Over the last century the frosts have moved by about 18~20 days at both the spring & fall ends of the summer, and so we've gained more than a month of frost-free days. That big shift happened between the 1940's and 1980's though, and since then things have been fairly constant.

In this chart we've added probabilities with the dashed, orange lines which are labeled "25% Chance" and "10% Chance." The 30-Year average line is the point where half of the first/last frosts will have occurred, but that means that 50% haven't occurred yet, and that is still pretty risky. The 25% and 10% lines add a safety factor to help avoid frosts that are early/late. They're calculated using the standard deviations for that last 30 years.

In the spring the 25% Chance line occurs 8 days after the average, and in the fall it's 7 days before. So if you use that as your guide then that shortens the season by 2 weeks, although for some years it will be more and for others it will be less. In the years since 2000, if you had followed the 25% line you would have been caught by late spring frosts 3 times: in 2015, 2009 (there were 5 late frosts that year) and 2002. And in the fall there were 2 years with early frosts: 2014 and 2007.

If a 25% chance of frost is too risky, then there's also the 10% line. That shortens the season by another 2 weeks compared to the 25% line, or by about a month compared to the average. If you had followed the 10% line since 2000 you would have been caught by one late spring frost, on May 23 2002. And the last time that a fall frost occurred before the 10% line was back in 1992.

The choice of the average, the 25% line or the 10% line is all about the risk of late frosts, and since I'm not a gardener I can't give any advice on that. But right now if we use the 10% risk as our criteria the frost-free season lasts from May 21st to September 10th, while a century ago it only lasted from June 18th through August 22nd.

Total Number of Frost-Free Days Each Year

In the previous charts today we've looked at the frosts in the spring and in the fall, and here we're looking at the gap between those two to measure the total length of Edmonton's frost-free season.

Right now the average length of the frost-free season is 140 days, up from 102 days a century ago. Some recent years like 2011 & 2012 were up at 174 and 169 days, while others like 1992 and 1989 were down around 92 and 104. The year with the shortest frost-free period was 1884 with 44 days, and the longest was in 1980 with 185.

This chart also shows the length of the season based on the 25% and 10% Chances of frost. As we saw earlier, using 25% is about 2 weeks shorter than the average, and 10% is about a month shorter. Looking at recent years, the only two which fell below the 111 days for a 10% chance were 1992 and 1989.

If you are more adventurous this chart also shows the average gaps between the 2nd frosts, and the 5th frosts. Risking the 2nd frost would add 10 days to the season, and stretching things all way to the 5th would add more than a month.

One thing to notice in this chart is the cluster of really high frost-free days that occurred in the late-1970s, with 7 years in a row all up above 160 days. Do all those long frost-free seasons mean that that was a particularly warm time period for Edmonton? Let's take a look:

Frost-Free Days and Edmonton's Warmest & Coldest Years

The background of this chart - the blue & orange bars - is one that we've used before, most recently in 2017 in Review - Temperatures. We won't go into all the details again today, but the short version is that it compares the overall temperature for each year to the 20th century average, with the warm years shown in orange while the cold years are in blue. Overlaid on top of that we've added the number of frost-free days for each year as a red dot.

Eye-balling off the chart it looks like there is a bit of a relationship between the number of frost-free days and how warm or cold each year was. For the consistently colder years of 1880-1940 the frost-free days were usually down between 80-120. And for the warmer years of 1970-today the range is more typically 120-160.

They're not a perfect match though, and the best demonstration of that is the years 1980 and 1981. As we saw earlier, 1980 had the longest period of frost-free days at 181, but it wasn't a particularly warm year coming in at 0.8°C above the 20th Century average. On the other hand, 1981 was Edmonton's warmest year at 3°C above average, but it's frost-free season was only a little bit high at 159 days. Earlier we'd also talked about 1992 which had a very low 92 frost-free days, but it was actually a fairly warm year at 1.7°C above average.

To really dig into this here's another chart:

This chart is just plain nerdery. It plots the number of Frost-Free Days each year against how warm or cold the year was. It doesn't have any real, physical meaning, but it lets us compare the relationship between the two pieces of data.

If frost-free days and warmness were a perfect match then all of these values would align along a single line, but there's some variability and so instead they form a cloud. There's definitely a relationship between the two, but the correlation is 0.21 so it's not particularly strong.

If you watch the dotted best-fit line that is in the middle of the cloud you can see that as time passes it has rotated counter-clockwise a bit, which just reflects the relationship between yearly temperatures and the frost-free days. As we've had more warm years recently the increase in the length of the frost-free season hasn't quite kept pace, and that has caused the line to tilt up a bit more.

Growing Season?

Finally, in doing research for today I found some definitions of "Growing Season" which were distinct from frost-free days. There were actually a few different definitions, and they didn't all agree, and so in this chart we are using the one from Alberta Agriculture and Forestry. They've defined it as:
The growing season period is based on an average daily temperature of at least 5°C. 
So the green lines in this chart show the 30-year average date on which our mean daily temperatures (High & Low) reaches 5°C. And through a fluke of averages, and the fact that our shoulder-seasons haven't changed much over the years, it turns out that the growing season today is about the same as it was a century ago. Using this method the season starts on April 17th, and it ends on October 14th. That works out to a total of 180 days (and that matches Alberta Agriculture and Forestry's number, which is a relief).

I'm not sure what this growing season measurement is useful for - I think that it applies to trees and perennials which don't care about frosts and which are here for the long haul? But since it is quite different from frost-free days I thought it was worth a quick mention.

So that's it for today. Because I don't garden I may have made some mistakes, or maybe I missed some useful information? If that's the case please leave a note in the comments, or you can reach me on twitter @yegwxnerdery.

Next week we'll be back with our standard April month-in-review.

Then in 2 weeks time we'll have Frost-Free Days: Part 2 - versus Round. We'll compare Blatchford to some of its neighbours, and we also might take a look at climate hardiness zones, although that might wait until a Part 3.


Almost 0cm of Snow (2018 Edition)

As of April 21st the International Airport has dropped to "Trace" amounts of snow on the ground:

The whole melt took two weeks, starting on April 8th at 31cm, and falling to almost-0 on the 21st.

Blatchford appears in this chart in green, and it hit 0cm on April 20th.

Last winter we marked this event exactly one month earlier, with the Airport hitting trace amounts on March 21st. That is show by the red, dashed line. Last winter there were some spring snowstorms though, which bumped things up again in April.

So the airport hasn't officially hit 0cm yet, but assuming that happens today then it will be pretty late, but not really late. We're still about a week ahead of when the snow first hit 0cm in 2013, 2011 and 2002. But in the last three years 2015, 2016 and 2017 were all really early winters, and we're several weeks behind those.


2017-2018 Winter-in-Review: Winter City Showdown - Part 2

Last week in the Winter City Showdown - Part 1 we looked at how temperatures for the winter of 2017-2018 compared on a day-to-day basis in Edmonton, Calgary, Winnipeg and Montreal.

Part 2 is going to be another marathon, and we're going to start with one of the most important aspects of winter - Snow!

Cumulative Snow

This chart shows the snowfall totals for the 4 cities during the winter of 2017-2018.

First, a bit of house-keeping:
  • the Edmonton data here is for the International Airport, because Environment Canada doesn't record snowfall at Blatchford
  • the Calgary data is for their International Airport.
  • the Winnipeg data is from winnipeg.weatherstats.ca. As far as I can tell Environment Canada doesn't have a station which records snowfall for Winnipeg anymore, which is weird. I don't know which station weatherstats.ca uses for their data, but it's all that I can find so we're going to run with it.
  • the Montreal data is from the main Environment Canada station.

With all of that said, Edmonton got off to an early start this year with a first snowfall on September 19th, and a total of 8cm of snow in September. We talked about that back when it first happened, and it was one of the earliest first snowfalls in recent memory (2004 and 2014 were both earlier). So this year was a bit unusual, and more typically our first snow waits until mid-October and even occasionally November. Edmonton's first lasting snow arrived around Halloween, when Edmonton, Calgary and Winnipeg all saw significant snow. Montreal's first snow was in early November, but it didn't really get going until mid-December.

Once Montreal took off though, it really took off. By late-December Montreal's total had passed the three prairie cites, and by mid-January it had received twice as much snow as any of them. As of April 15 Montreal had received 251.2cm, Calgary had 173.3cm, Edmonton was at 106.5cm, and Winnipeg was at 84.2.

Next we're going to take a closer look at the snowfall for each city, including their recent averages. We'll zip through these with some quick commentary, and we'll start with Calgary.

Cumulative Snowfall for Calgary
Here we have the same chart that we were just looking at, except this time it only shows Edmonton and Calgary. After Edmonton's early start the two cities were fairly close through the end of February. But in February and March Calgary took off.

Calgary's average and recent maximum amounts are shown here as the dotted red lines. Calgary's average snowfall total each winter is typically a bit higher than Edmonton's: about 140cm for Calgary compared to 125cm for Edmonton. This winter Edmonton is a bit below average, but Calgary is well above at 173.3cm. With one-and-a-half months of spring left, Calgary is getting fairly close to its snowiest recent years of 2008 and 1997.

Cumulative Snowfall for Winnipeg

Winnipeg's snowfall data isn't great, and so there are a lot of caveat's with this chart. As previously mentioned, the 2017-2018 data doesn't come from Environment Canada, which is unfortunate. The historic data for the average and maximum does come from Environment Canada's station at the Winnipeg International, but that data stops in 2007. So the Edmonton history here is for 1995-2018, while for Winnipeg it only includes 1995-2007.

With that said, the dotted green lines in this chart show Winnipeg's average and maximum for 1995-2007. And based on those years Winnipeg's snowfall totals were pretty close to Edmonton's. For 2017-2018 then, Winnipeg's 84.2cm is 20cm below Edmonton, and below average for Winnipeg.

Cumulative Snowfall for Montreal

Here we have Montreal's cumulative snowfall throughout the winter, along with it's recent average, maximum and minimum shown as the dotted lines. The Montreal data is also missing a few years of records - from 2012-2015 - so it's not a perfect comparison, but it's close. The scale of this chart is not the same as the others, because it needed to be increased to fit Montreal's snowiest year.

Montreal's 251.2cm of snow in 2017-2018 is more than double Edmonton's 106.5cm. But as we can see in the chart that's not very extreme for Montreal, and is only about 25cm above the average. Montreal's snowiest recent winter was 2007, which had a total of 371mm. And if we look at the line for Montreal's least-snowy winter, at 150cm that was still almost 25cm above the average amount of snow that Edmonton gets.

To take another look at snow, next we're going to break the numbers up by month.

Monthly Snowfall

Here we have the snowfall for each month of the winter in Edmonton, Calgary, Winnipeg and Montreal.
  • Again we can see that Edmonton got off to an early start with 8cm in September. And again, I do want to stress that that was unusual - it was Edmonton's snowiest September since 1995.
  • Edmonton also had a fairly snowy October with 15cm, compared to 1cm in Calgary, 4cm in Winnipeg, and nothing in Montreal.
  • For November Edmonton and Winnipeg were around 20cm, with Calgary up at 27cm and Montreal down at 6cm.
  • And then in December Montreal took off with 61cm, while Edmonton was way down at 3cm.

For the rest of the winter Edmonton was pretty average. But lets take a closer look at the individual cities again:

Monthly Snowfall for Calgary

Here we have the monthly snowfall for Calgary, and the dotted lines show its recent average and maximum amounts.

We saw earlier that Calgary has had a total of 173.3cm so far this winter, which is well above the average. And this winter the well above-average months were November, December, February and March, with February setting a new recent maximum at 43cm. 

During April & May Calgary typically gets more snow than Edmonton does, so we'll need to wait and see where Calgary ends up for this winter.

Monthly Snowfall for Winnipeg

This chart for Winnipeg has all the previous caveats about incomplete data. But again, on average the monthly snowfall in Edmonton and Winnipeg are pretty similar. And the monthly totals for 2017-2018 were pretty similar too, although Edmonton had a low December and Winnipeg had a low February.

Monthly Snowfall for Montreal

For Montreal, once again the scale of this chart needs to be different from the others so that we can fit Montreal's maximum in.

Looking at the dotted line for Montreal's average, we can see that for each month from December through March Montreal's average is more than double Edmonton's. And this year in particular, for those 4 months Montreal received 227cm of snow compared to 62cm for Edmonton.

For Montreal the 86cm of snow this January was well above average, and it was close to the very snow January 1999 which had 95cm. Montreal's snowiest month since 1995 (with the caveat that records for 2012-2015 are missing) was December 2007 with 113cm.

One final thing to notice from this chart is Montreal's maximum snow for May, which is way down at 0.2cm. In Edmonton, Calgary and Winnipeg snow in May happens about half of the time. But Montreal really doesn't get snow in May, with 2016 being the only recent year to even get a dusting. So Montreal gets a lot more snow than the prairie cities, and it's crammed into November-April instead of October-May.

All of these cities might see more snow before the end of spring, and if anything really notable happens (like maybe Calgary will cross the 200cm mark) we'll check back in.

We're going to finish today by taking one final look at temperatures. Last week we looked at how Edmonton's temperatures compared to the other cities on a day-by-day basis. Today we're going to see how the winter of 2017-2018 compared to other winters, for each of the cities.

Edmonton's Warmest & Coldest "Winters" (November 1 to April 15)

This chart ranks temperatures in Edmonton for the period of November 1st, 2017 through April 15th, 2018 compared to other winter. We use this type of chart quite a bit, and if you are interested in the details behind it the full explanation is here.

We ran a version of this chart at the end of March, and at that point the winter of 2017-2018 ranked as #67 out of 138 years. That version of the chart is here. Since then though we've had the coldest-April-since-forever, and that has dropped us down in the rankings to #77. When we include the first 2 weeks of April the winter of 2017-2018 was 0.3°C below the 20th Century average, and about 2°C below the recent average.

How did this winter treat the other cities?

Calgary's Warmest & Coldest "Winters"

Here we have Calgary's warmest and coldest winters.

This year Calgary and southern Alberta were complaining that the didn't get enough chinooks, and Calgary's winter ranked as its #100 warmest. It was -1.3°C below the 20th Century average, and about 2.5°C below the recent average. That made it colder than 2013-2014, but still warmer than 2010-2011.

Looking at the warmest winters, for both Edmonton and Calgary most of the warmest winters have been in the past 40 years. But the winter of 1930-1931 is prominent for both cities, coming in 1st spot for Calgary and 3rd for Edmonton.

Winnipeg's Warmest & Coldest "Winters"

2017-2018 was also a coolish winter in Winnipeg, coming in at #82. It was 0.7°C below the 20th Century average, or about 1.5°C below the recent average.

Comparing this chart to Edmonton and Calgary, Winnipeg's winters are a bit more variable. In recent years Edmonton's two coldest winters were 1995-1996 and 1996-1997, which were both at about 2°C below the 20th Century average. Those cold winters were apparently volcano-related, and we see them in Calgary's chart at 3°C below the 20th Century average, and here in Winnipeg at 4°C below. But Winnipeg also had a very cold non-volcano-related 2013-2014 at 4°C below the 20th Century average, compared to about 0.7°C below for Calgary and 1°C below for Edmonton.

And 1930-1931 shows up again here: 1st warmest for Calgary, 3rd for Edmonton, and 7th for Winnipeg.

Montreal's Warmest & Coldest "Winters"

For Montreal the winter of 2017-2018 was just a touch warmer than the 20th Century average at 0.3°C, but that still meant it was about 0.7°C cooler than the recent average for winter.

Comparing this chart to the prairie cities we can see that Montreal is quite a bit less variable - it's warmest winters were 4°C above the 20th Century average, and it's coldest were 3.5°C below. For Edmonton and Winnipeg the most extreme winters are 6°C in either direction.

All 4 Cities Together

And when we roll all of the cities together this is what we get. If you focus on certain years - like 1930-1931, or the "volcano" winters of 1995-1997 - you can watch the similarities and differences for the cities.

The Hypothetical Horserace

And for some final nerdery, with this chart we ask: hypothetically, if Edmonton experienced the same temperatures as Calgary, Winnipeg or Montreal, how would that rank compared to a typical Edmonton winter?

This "horserace" chart is one that we've used quite a few times before, and the full details of what exactly is going on are explained here. Generally though, this tracks how much warmer each day of the year was compared to Edmonton's 20th century average - warm days get points and cold days lose them. And what we're doing here is pretending that Edmonton experienced the same temperatures as Calgary/Winnipeg/Montreal, and then seeing where we end up.

For Calgary the winter of 2017-2018 was a cool one, coming in at #100. If Edmonton had had the same temperatures each day this winter would have ranked as #57, or about the same as 1993-1994. That's not cold, but it's not really warm either.

For Winnipeg the winter of 2017-2018 ranked as #82, but with those temperatures in Edmonton it would have been down at about #131. The last time that Edmonton saw a winter that cold was in 1964-1965.

And Montreal's #57 would have been a pretty warm winter in Edmonton, coming in at about 13th spot or tied with 1999-2000.

Going back to the Edmonton chart which we saw earlier, this is what the other cities' winters would look like:

We don't want to take this chart too seriously - hence the use of "Equivalent~ish." But this at least gives us a sense of how the temperatures for what was a cool winter in Calgary, Winnipeg and Montreal would compare to Edmonton's winter history.

In Parts 1 & 2 of our Winter City Showdown we've now seen that there are a lot of different factors that make up a winter:
  • Edmonton and Calgary have a reasonable amount in common, with the main difference being Calgary's warmer winter Highs, although that difference isn't as big a deal for the Lows. The snowfall for the two cities is usually pretty similar, but some years (like this one) things can diverge.
  • Not surprisingly Winnipeg is a colder version of Edmonton, with about the same amount of snow.
  • And Montreal's winter really is very different from these 3 prairie cities, with warmer Highs & Lows, but with a lot more snow.


2017-2018 Winter in Review: Winter City Showdown

As winter very, very, very slowly takes its leave, today we're going to see how the winter of 2017-2018 compared in Edmonton, Calgary, Winnipeg and Montreal.

Last year we did a series looking at how Edmonton's average temperatures and precipitation throughout the year compare to some of Canada's other winter cities:
Those give a general idea of the differences for the cities throughout the year. But today we'll be digging into the specifics of the winter of 2017-2018 on a day-to-day basis.

Before we jump in, first lets take a quick look back at how Edmonton's winter went:

Edmonton's 2017-2018 Winter: Low Temperatures

Even though winter has decided to hang around for a few weeks into April, to keep things simple for today we're going to use November 2017 through March 2018 as the boundaries of "Winter."

And for Edmonton those 5 months went something like this:
  • really cold start to November - right at the bottom of our typical temperature range.
  • really warm December - right at the top of the range.
  • really cold deepfreeze from Christmas to New Year's - bottom of range again.
  • January bounced between warm and cold.
  • February was down at the bottom of the range again.
  • March was pretty average...until it ended with a surprise deepfreeze.

So that was a quick reminder of Edmonton's winter of 2017-2018, and if you are interested in more details they are all here:

Now we're going to see how last winter in Edmonton compared to other locations. There will be a lot of charts today as we work our way through each of the cities, and we're going to start with something close to home:

Edmonton International High Temperatures

The rest of the charts today are going to follow a similar format, and starting with the High temperatures for the International Airport is a good example of how this will work:
  • These charts will all start by showing the daily temperatures for Edmonton and for the other location. A counter shows how many of the days Edmonton was warmer, and how many days the other location was.
  • Then the chart will switch to areas, to give a better visual sense of the gaps between the two sets of temperatures.
  • A dotted line for the 7-Day Average Difference will appear, to show roughly how much warmer or colder the week was. If that dotted line is above 0°C then that means that Edmonton was warmer that week, but if it's below then Edmonton was colder.
  • And finally, the 10 largest gaps will be highlighted with the date that they occurred, and with the temperatures at the two locations.
That sounds like a lot of rules to remember, but this post is already going to be really long. By stuffing all of that information into a single chart we'll hopefully be able to get through this before the winter of 2018-2019 starts.

So with all of that said, what can we learn from the High temperatures for the International Airport?
  • Not surprisingly, the temperatures for Edmonton and the Airport track really closely to one another. When one warms up or cools down, the other does too.
  • Edmonton's Highs were warmer than the Airport's for 120 of the 151 days. The airport was warmer for 25 days, and there were 6 days where the two locations were tied.
  • On average the Highs in Edmonton were 1°C to 3°C warmer than the Airport for most of the winter.
  • For the Top-10 largest gaps, 9 of them had Edmonton warmer than the Airport. The largest difference was 6.3°C on February 5th, with Edmonton at -10.1°C and the International at -16.4°C. The rest of the Top-10 are all 4°C to 5°C difference. The one time that the Airport was much warmer than Edmonton was January 9th with Edmonton at -9.6°C, while the Airport was 5.9°C warmer at -3.7°C.

We did a similar comparison for Edmonton and the International last year for the winter of 2016-2017, and if you're interested in those results they are at the bottom of versus - The Edmonton International Airport: Part 2.

Edmonton International Low Temperatures

Here we have the Low temperatures for Edmonton and for the International Airport.
  • Edmonton's Lows were warmer than the Airport's for 136 of the 151 days, and the Airport was warmer than the city only 15 times.
  • On average the Lows in Edmonton were 2°C to 4°C warmer than the Airport, but that rose up to an average of 7°C during a deepfreeze in early-February, and then again in mid-March.
  • For the Top-10 largest gaps, all 10 of them had Edmonton warmer than the Airport.
  • The largest difference was 13.3°C on February 8th with Edmonton at -18.8°C and the Airport way down at -32.1°C. Another notable day was February 4th with Edmonton at -30.7°C and the Airport way down at -39.3°C.
  • The other largest gaps were all in the range of 8°C to 10°C and happened during the February deepfeeze, and then again later in March.

Calgary High Temperatures

Here we are comparing the High temperatures for Edmonton-Blatchford against the Calgary International Airport.

Anytime we do comparisons with Calgary I need to mention the caveat that Environment Canada doesn't have a central weather station for Calgary. And so these temperatures are likely a  bit colder than if they were recorded nearer downtown. We looked at the differences for outlying and airport stations last year in The Edmonton International Airport: Part 2, and saw that the Edmonton International is really, abnormally cold. So while this isn't perfect, Blatchford is probably the better comparison for the Calgary International than the Edmonton International would be.

With that out of the way, what do we have here?
  • Calgary likes to think of itself as warmer than Edmonton, and...yeah. Its High temperatures were warmer for 2/3 of the winter, with Edmonton picking up the other 1/3.
  • Even with Calgary being consistently warmer, we can see that the two cities track very closely to one another. Calgary's December heatwave was several degrees warmer than Edmonton's, but Edmonton was still pretty warm. The most dramatic divergence was right at the end of January when Calgary's Highs shot up above freezing while Edmonton stayed down around -8°C, but that was only for 2 days.
  • On average throughout the winter Calgary's Highs were 0°C to 5°C warmer than Edmonton, although there was a week at the beginning of March where Edmonton averaged about 3°C warmer.
  • For the Top-10, Calgary was warmer for all of them. The largest difference was November 26 with Calgary way up at 14.6°C, and Edmonton 16.3°C colder at -1.7°C. The rest of the Top-10 were all also differences of 10°C to 15°C.
  • Edmonton's warmest day compared to Calgary was February 19th with Edmonton at -7°C and Calgary 5.9°C colder down at -12.9°C.

We did a similar look at Calgary last year, and you can read the results in 2016-2017 Winter in Review - versus Calgary. Calgarians would say that the winter of 2017-2018 has been unusually cold and unfair to them, but last year in 2016-2017 Calgary was warm for 96 days compared to Edmonton's 49, which is pretty similar to the 100/49 split that we saw this winter.

Calgary Low Temperatures

Here we have the Low temperatures for the Calgary International Airport compared to Edmonton-Blatchford.
  • When we looked at the High temperatures we saw that Calgary was consistently warmer than Edmonton. For the Lows the cities are much closer, with Calgary at 80 days and Edmonton at 71. 
  • The average difference fluctuates from Edmonton being 4°C warmer to Calgary being 5°C warmer.
  • The Top-10 largest differences are split between the cities. The very largest was 12°C on February 13th with Calgary up at a Low of 1.9°C while Edmonton was at -10.9°C. Edmonton was warmer for the 3rd largest difference, which was 9.4°C on December 11th, with Edmonton at -2.2°C and Calgary at -11.6°C.
Last year we did this comparison as well, and for the winter of 2016-2017 Calgary was warmer for 79 days compared to Edmonton's 76. That's again pretty close to the 80/71 split this year.

Winnipeg High Temperatures

And now we're moving on to Winnipeg. Environment Canada has two main weather stations for Winnipeg - the Airport and the Forks - and we'll be using the temperatures for the Forks. And again, the difference between those two stations was something that we looked at last year, if you're interested in how they compare.

So how does did Winnipeg's winter compare to Edmonton's:
  • In the charts for the Edmonton International and for Calgary, we saw that their temperatures were pretty closely tied to Edmonton's. That's not as quite as true for Winnipeg:
    • Edmonton's November was really cold, but Winnipeg's was pretty normal.
    • Edmonton December was really warm, but Winnipeg's was pretty normal.
    • Both cities (and Calgary too) had a deepfreeze right around Christmas.
    • Both cities (and Calgary too) had January warmspells, with Winnipeg following a few days behind Alberta.
    • And after that things tracked pretty closely.
  • Edmonton's Highs were warmer for 92 of these days, compared to 58 for Winnipeg.
  • The average difference fluctuated throughout the winter. Winnipeg was 5°C warmer through November, and then briefly in March. In parts of December & January Edmonton averaged 10°C to 15°C warmer.
  • For the Top-10 gaps, Edmonton was warmer for 9 of them, and Winnipeg was warmer for 1. The largest gap was January 3rd with Edmonton at 3.4°C, and Winnipeg 24°C colder down at -20.6°C. The second largest gap is a two-way tie, with Edmonton being 23.1°C warmer than Winnipeg on January 4th, and then Winnipeg being 23.1°C warmer than Edmonton on January 10th. For the rest of the Top 10 Edmonton was 15°C to 20°C warmer than Winnipeg.
  • The biggest gaps here aren't really as meaningful as they were for the Airport or Calgary, since the temperatures for Edmonton and Winnipeg don't follow each other as closely. But they're still interesting trivia. 

Winnipeg Low Temperatures

Here we have the Low temperatures for Edmonton-Blatchford and the Forks in Winnipeg:
  • For the Lows Edmonton was warmer for 87 days, and Winnipeg the other 64.
  • The average difference for the Lows was pretty similar to what we just saw for the Highs: Winnipeg was 5°C warmer through November, and then briefly in March. In parts of December & January Edmonton averaged 10°C to 15°C warmer.
  • The Top-10 largest gaps were split, with Edmonton warmer for 7 and Winnipeg warmer for 3. The largest was 19.6°C on January 4th when Edmonton's Low was -7°C and Winnipeg's was -26.6°C. The 2nd largest had Winnipeg on top, when its March 5th Low of -3.1°C was 18.7°C warmer than Edmonton's at -21.8°C.

Montreal High Temperatures

Moving on to Montreal, here are its High temperatures compared to Edmonton's:
  • Here we can see that the two cities temperatures have almost nothing in common - when Edmonton is cold Montreal is warm, and when Montreal is cold Edmonton is warm. Both cities shared the Christmas deepfreeze, but that's about it.
  • Montreal's Highs were warmer for 97 days, compared to Edmonton's 54.
  • The average, weekly difference is all over the place - Montreal averaged 20°C warmer for part of November, and Edmonton was 15°C warmer for part of December. For a lot of the winter though, Montreal averaged 5°C to 10°C warmer than Edmonton.
  • Of the Top-10 gaps Montreal was warmer for 9 days, and Edmonton was for 1. The largest was January 12 with Montreal at 10°C and Edmonton 30°C colder at -20°C. Edmonton's biggest win was just a week before that on January 6th, when it's High of 5.2°C was 25.4°C warmer than Montreal's -20.2°C.

Montreal Low Temperatures

And here we have the Lows for Montreal:
  • As we saw with the Highs, there isn't much in common here.
  • In Montreal the Lows were warmer for 102 days, compared to 48 in Edmonton.
  • Looking at the weekly average, Montreal's Lows were 5°C warmer than Edmonton's for a lot of the winter. But there were a few times when that opened up to 10°C or 15°C. And Edmonton had 3 warmspells where it was 10°C to 15°C warmer than Montreal.
  • For the Top-10 gaps Montreal was warmer for 8, with Edmonton at 2. The largest was January 11th, with Montreal's Low at -2.4°C, and Edmonton 25.4°C colder and way down at -27.8°C. And just like we saw with the Highs, Edmonton's biggest win was about a week earlier on January 7th with a Low of -4.6°C compared to Montreal's -24.9°C.

We're going to do one final comparison, for interest's sake:

Calgary versus Montreal High Temperatures

Here we have the High temperatures for Calgary and Montreal:
  • When we compared these cities to Edmonton, Calgary was warmer for 100 days and Montreal was warmer for 97. When we compared them to each other they are basically tied, with Calgary at 76, Montreal at 74.
  • The weekly average is all over the place again, because the temperatures for Calgary and Montreal don't really track together. Calgary is mostly warmer than Montreal during a couple of warmspells, and then for the rest of the winter Montreal was 5°C to 10°C warmer than Calgary.
  • For the Top-10 gaps Montreal was warmer 7 times, compared to Calgary's 3. The largest was January 11th with Montreal at 7°C and Calgary at -23.3°C. Calgary's biggest win was January 6th with a High of 9.2°C compared to Montreal's -20.2°C. (and these were very similar to the largest gaps for Edmonton-Montreal that we just looked at)

Calgary versus Montreal Low Temperatures

And for our final comparison, here we have the Low temperatures for Calgary and Montreal:
  • When we compared the Lows for Calgary and Edmonton they were pretty close, with Calgary warmer for 80 days compared to Edmonton's 71. When we compared Montreal to Edmonton it was 102 days for Montreal, compared to 48 for Edmonton. And now our Montreal-Calgary comparison has a lot in common with our Montreal-Edmonton, because Montreal's Lows were warmer for 103 days compared to Calgary's 47.
  • Looking at the weekly averages Calgary was warmer - sometimes 15°C warmer - in December and January. But for most of the rest of the winter Montreal was 5°C to 10°C warmer.
  • For the Top-10 gaps Montreal was warmer for 8 compared to Calgary's 2. The largest was January 11th (same as Edmonton's), with Montreal's Low at -2.4°C, and Calgary 25.2°C colder and way down at -27.6°C. And Calgary's biggest win was a week earlier on January 6th with a Low of -1.5°C compared to Montreal's -24.7°C.

So that was a bit a of a marathon, but hopefully now we have a better sense of how the winters in these cities compared.
  • Edmonton and Calgary have quite a bit in common - although Calgary definitely has higher Highs.
  • Edmonton and Winnipeg temperatures were fairly similar in the last half of the winter, but moved in opposite directions during the first half.
  • And temperatures in Edmonton and Montreal don't have much in common at all, with Montreal warm while Edmonton was cold, and visa versa. Montreal averaged about 5°C warmer than Edmonton for most of the winter, and that matches the long-term trends we saw last year.
(Winnipeg fans might be wondering why there are no Winnipeg v. Calgary and Winnipeg v. Montreal charts? Sadly we're going to leave those to the imagination, because things are already running really long.)

High Temperature Totals

Bringing it all together, here are how the High temperatures for the winter were distributed for the 4 cities.
  • Calgary is the big winner for days of 5°C or more, with 45. That beats Montreal's 35, Edmonton's 21, and Winnipeg's 6.
  • Montreal wins for days above freezing though, with 88 compared to 80 for Calgary, 57 for Edmonton and 36 for Winnipeg.
  • For Highs of -20°C or colder Montreal had 2, Calgary 5, Edmonton 6 and Winnipeg 11.

Low Temperature Totals

And here we have the Lows:
  • Montreal is quite a bit different than the prairie cities, with 62 relatively mild Lows of -5°C or warmer. Calgary had less than half that at 26, Edmonton had 23, and Winnipeg had 19.
  • At the other end of things Winnipeg takes the lead with 42 Lows of -20°C or colder, compared to 31 for Edmonton, 28 for Calgary, and 18 for Montreal.
  • At the very furthest end, this winter the two Alberta cities both recorded 3 Lows of -30°C or colder. Winnipeg only had 1, and Montreal had none.

When we group things together like that we see that most of the interesting stuff happens at the extremes - the Highs and Lows above freezing or down below -20°C. In the middle of that range the cities have a lot in common.

And with that we're going to call it a day. Next week we'll be back with the Winter City Showdown - Part 2.

In Part 2 we'll take a look at what is possibly the most important Winter City metric: snow. We'll also see how the winter of 2017-2018 compared to historic winters. For Edmonton we know that this winter was a little warmer than the historical average, but colder than the recent average. So how did it compare for Calgary, Winnipeg and Montreal? (spoilers: yes Calgary, for you folks this winter actually was a little cold)