2021/05/01

April 2021 Review

 It's time for our look back at April 2021, but for this month there's a caveat:


The Blatchford weather station near downtown Edmonton had no readings from April 1st through April 8th. That is the longest outage at Blatchford in 28 years, going back to 1993. But rather than leaving all those days blank we have instead substituted the temperatures from the South Campus station which should hopefully be a close enough match.


High Temperatures

April 2021's Highs were generally pretty close to average, with the month starting a little warm and then getting a little cool near the end. The two days closest to the top of the range were April 1st's 18.9°C, and April 30th's 22.4°C was a warmest-in-30-years High. We didn't really get near the bottom of the range with April 27th's 4.4°C as the coldest High.

Overall there were 18 Highs which were warmer than the 30-year average and 12 which were colder.


On average in April we will have 2.5 days with Highs below 0°C, but in 2021 we didn't have any. In April we also average 2 days which hit 20°C, and in 2021 we squeaked in above that with 3: 20.3°C on the 16th, 20.8°C on the 21st, and 22.4°C on the 30th.


Low Temperatures

For the Low temperatures April 2021 started above average, but the final two weeks were mostly below average, and were also mostly below freezing. Overall 14 Lows were above the 30-year average compared to 16 below.


On average in April we have 17 Lows below freezing, and 2021 was a little cooler than that with 20. The coldest Low was -6.1°C on April 23rd. Looking at the blues and pinks in this chart, normally the freezing Lows start to become rare after about mid-April, but this year we had a solid week of frosts right near the end of the month.

It's possible that the frost which we had on April 28th will end up as the final frost for the season, but we won't really know for a few more weeks:   


The Final Frost?

Last spring in 2020 the final frost at both Blatchford and Stony Plain was very early on April 19th. Meanwhile at the International the final frost came nearly a month-and-a-half later on June 5th. 

More typically the 30-year average date of the final frost for Blatchford is around May 6th, Stony Plain is a few days later on May 10th, and the airport is a few weeks after that on May 23rd. Please keep in mind though that the date of the "average" final frost means that half of the time it happens before that date, and half of the time it happens after.


Warm and Cold Months

As we have already seen, for April 2021 the Highs were a little bit above average while the Lows were a little bit below. The average High of 12.1°C ranked as Edmonton's 49th warmest April since 1880, while the average Low of -1.6°C was in the 81st spot.


Looking at the recent history of warm and cold months April 2021 is a small orange bubble, at 0.6°C warmer than the 20th century average. Looking at the line for April there are still lots of blue bubbles, including 2020. And the last time that we had a notably warm April was in 2016.


Across Canada

Looking across Canada, in the west the temperatures for April 2021 were fairly close to the 20th century average, ranging from Calgary at 0.7°C above its average down to to Winnipeg at -0.7°C below its average.

In central and eastern Canada it was generally warmer though, with Ottawa and Montréal at 3°C warmer than their long-term averages.


Consistent April

In Edmonton April is one of the months which has seen the least temperature change since modern records began in 1880. This chart has the average temperatures for January, April and July:
  • For our coldest month, January's average Highs have increased by 8°C and the Lows have increased by 10°C.
  • For our warmest month, July's Highs have increased by 1°C while its Lows have increased by 4°C.
  • But for April the average Highs have actually decreased by 1°C, while the average Lows have increased by 2°C. 
  • October isn't shown here (although it can be added using dropdown on the lower left) but it is basically right overtop of April, and its Highs have decreased by 0.6°C while the Lows increased by 2°C.
So for the shoulder-season months of April and October Edmonton's temperatures are not very different from where they were a century ago. All of the other months have seen bigger shifts, with the biggest changes happening in January and February.


Are April's temperatures flat~ish everywhere? Here we have the January, April and July histories again, but this time they are for Vancouver, Winnipeg and Montréal:
  • Vancouver is obviously a lot warmer than Edmonton, or the rest of Canada. Its Lows have gone up by around 2°C for January, April, and July. For the Highs January has warmed by 2°C while the averages for April and July are both 0.3~0.4°C cooler than a century ago.

  • Winnipeg is a lot like Edmonton, unsurprisingly. January has warmed a lot, and July has warmed a bit. April is pretty flat, but both the High and Low are up by about 1°C.

  • Finally for Montréal the Highs for January, April, and July are all up by about 2°C. For the Lows April and July are both up by about 1.5°C, while January is up by 3.5°C.
Those are just a few examples, and all of the other months and cities can be accessed through the dashboard. This is just to show that Edmonton's experience isn't completely unique, but also that things do vary depending where you are in the country.


April Snowfall

In April 2021 the International Airport recorded 5.2cm of snow. That's below April's average of 15cm, and was just a bit below the 5.5cm that we got in April 2020.


Winter 2020-2021 Snowfall

For the winter of 2020-2021 so far the International has had a total of 73.5cm, which is below the average of 116cm, and is a bottom-5 winter for the International, going back to 1960.

The "winter" isn't necessarily over though, because in May we have roughly of 50/50 chance of seeing more snow. Our average snow for May is 5cm, but that is split between a bunch of years with no snow, and bunch of years with 7, 10 or 20cm+ of snow. (May 2003 had 38cm of snow at the International).


Across the country Edmonton's 73.3cm of snow was below all of these other cities, except for Winnipeg at 66.2cm and Vancouver at 12.6. And this year Calgary doubled us with 148cm. So Edmonton and Winnipeg both had very low snowfalls this winter, but for the rest of these cities the totals were all pretty typical.


Total Precipitation

April is the month where we typically start to transition from snow into rain, and in April on average we get 28mm of total (snow + rain) precipitation.

For April 2021 the International had the most precipitation of all of the stations in the region with 12.8mm. Blatchford had 5mm and Stony Plain had 6.6mm.

In recent years April 2015, 2019 & 2020 were all similarly below around 10mm, so April 2021 is low, but not really unusual.


For 2021 so far though all of the months have had below average Precipitation. The International has had the most overall with 40.9mm, which is its 3rd lowest January-April going back to 1960. Stony Plain's 22.9mm is its 2nd lowest going back to 1966. And Blatchford's 19.2mm is a bottom-10, going back to 1880.


May Temperatures

Looking ahead to next month, May has not had a High below freezing since 1959, but about one third of the time there will be 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. And May 2015, 2016 & 2017 all had almost a week of 25°C days, while 2018 had almost 2 weeks. And from 2016-2019 we had 4 May's in-a-row with a day which hit 30°C.

For Low temperatures, about a quarter of the time our final frost will be in April, and so May will have no Lows below 0°C. More typically though, May will have a handful of frosty nights.

May Snow

And no one want to hear this, but the International records snow about half of the time in May. Recently May 2016, 2017 & 2018 were snowless, but 2019 had 4 snowfalls and 2020 had 1.

2021/04/11

April 10 2021 - Spring Snow

It happened: on April 10th we had a nice, big, spring snowstorm. Hopefully everyone enjoyed all of the "second-winter" Hobbit jokes, but how unusual are April snowstorms?

April Snow
In April on average we get about 15cm of new snow. The last time that we had a snowless April was 2005 at Blatchford, or 1998 at the International Airport.

In May we average another 5cm. That can vary from snowless Mays like 2016-2017 and 2011-2013, to 2020 with 4cm, 2015 with 12cm, 2010 with 28cm or all the way to May 2003 with 38cm.

Blatchford doesn't record snowfall anymore, but on April 10, 2021 the International recorded 4.2cm of snow. If that is all the snow that we get during this month then this April would be a bottom-20 year at the International.

But when do we typically have our final snowfall for the year?


Final Snow
If this April 10th storm really is our final snow for the year it would be the earliest final snowfall at the International since 1998.

I'm sure that no one really wants to hear this, but from the past 10 winters the average date of the final snow is...May 1st. (this chart shows the 10-year average as April 25th because it's including 2021's April 10th in the calculation, but without 2021 it falls back to May 1st.)

In both 2020 and 2019 it was on May 4th, in 2018 it pretty early on April 16th, and both 2017 and 2016 were April 24th. And then a year like 2011 was really late on May 13th.


Spring Snowstorms
Our April 10th storm was 4.2cm, and so for comparison this chart shows every 4cm+ storm for April and May. This year's storm is the small~ish bubble furthest to the right.

Large April storms are pretty common, and they might drop-off a little bit after mid-April, but they don't really disappear until after the first week of May. And even then sometimes we will get big storms in mid-May, or even in late-May like the 7.8cm we got in 2010 on May 29.

So enjoy this second-winter. But keep in mind that there could be a third or fourth yet to come.

2021/04/01

March 2021 Review

Today we are going to take a look back at the weather for March 2021.

We will talk a bit about the winter in general too, but if you are interested in how the winter of 2020-2021 compared overall we had a detailed look at it a few weeks ago in 2020-2021 Winter In Review: Temperatures.




March 2021 High Temperatures
Here we have the High temperatures for March 2021. We ended up with 5 Highs which were colder than the 30-year average, compared to 26 which warmer. And that included 2 warmest-in-30-year Highs on March 17th at 12.6°C and March 18th at 15.8°C. 

One of the cruel tricks of Alberta weather is that the start of March was warmer than the end. We jumped from "winter" to "spring," and it felt let we were on the way to "summer," but unsurprisingly the real summer is still many months away. The end of the month certainly felt a lot colder than the start did, but it was all pretty typical for March.

Looking at the numbers we only had 2 Highs below freezing, compared to an average of about 11 for March. On the other end we had 10 Highs above 10°C, when March averages about 4. And that included 1 High above 15°C, which in recent years had only happened in 2019, 2015, 2010 and 2004.
 

March 2021 Low Temperatures
For the Low temperatures we had 8 below average, compared to 23 above. And that included 3 warmest-in-30-year Lows, including a new record-warmest Low of 3.9°C on March 14th.

Our coldest Low this month was -14.1°C on March 14. In total we had 3 Lows below -10°C, while March averages 10. The only recent Marches which didn't hit -15°C were 2010, 2016 and now 2021. March 2017-2020 all hit -20°C at least once, with 2019 having 3 Lows which dropped below -25°C.
 

Warm and Cold Months
So overall March 2021 was a pretty warm month. 

Its average High ranked as 5th Highest, and 5.8°C warmer than March's average. It was the warmest March Highs since 4th place 1988, which was just tiny bit warmer. Before that we need to go back to 1910, which is in 1st place with an average High of 10.7°C. 

The Lows weren't quite as unusual, ending up in 14th spot at about 3.5°C warmer than average. Recently March 2016, 2015 and 2010 all had warmer average Lows.

In this chart orange bubbles represent months where the Mean temperature (the average of the Highs and the Lows) was warmer than the 20th century average, while blue bubbles were colder.

March 2021 is a fairly large orange bubble at 5.8°C warmer than the 20th century average. That is about the same size as March 2016 and a little bit bigger than March 2015. It follows a cool February and a warm January this year.
 

Across Canada
Looking across Canada it was a warm March in all of these cities, but especially on the prairies. Winnipeg was at the top at 6.8°C warmer than its 20th century average temperature for March.
 

2021 So Far
In this chart the red line shows how the temperatures each day compared to the average temperature for the 20th century. When days were above-average days the line goes up, and for below-average days it drops. 

After 3 month of 2021 we have had Edmonton's 25th warmest start to a year. Things got off to a really warm start in January, but the red lines all take a significant dip for the coldsnap in late-January and early-February. But after that things start climbing again through March.

In this chart each of the bars represents the average temperature for January-March compared to the 20th century average for each of these cities.

Looking across the country again, most of the cities here have had a top-25 warmest January-March, with Toronto, Calgary and Vancouver as the exceptions at around the 40th spot.
 

Snowfall

The International Airport recorded 5.5cm of snow in March, which is below the average of 19cm. This winter February's snow was right on the average, November's was above, and all of the other months have been low.
 

For the winter so far we have had 68.3cm of snow, which is well below the average of 100cm for this point in the winter. But, in April and May we do average another 20cm of snow, so the snow season probably isn't over.
 

This chart has the snowfall totals for cities across Canada. It is a little tough to read, but out 68.3cm of snow just pushes us above Winnipeg's 66.2cm. Next is Toronto at 100cm. Calgary, Ottawa and Montréal are all from 138-164cm, and St. John's is up at 282cm.

Most of these numbers are within the typical ranges for these cities. The biggest outliers are Edmonton and Winnipeg which are quite low, while Calgary's 138cm is above its average of 112cm.
 

Snowdepth
In terms of snowdepth, the warm temperatures at the start of March gave us an early melt. Blatchford's last recorded snow was on March 9th, and the International's was on March 20th. But then the International did pop up to 4cm with some fresh snow on March 29th.

And across Canada the warm March meant that all of these stations were snow-free by the end of March.
 

April Temperatures
For April temperatures on-average it only has 3 Highs below 0°C, and about three-quarters of the time April will have a day hit 20°C. 2001, 2015, 2016, and 2018 all had days hit 25°C.

In recent years April 2020 and April 2018 both started quite cold though. We hadn't had a -20°C Low in April since 1982, but April 2nd 2020 broke that streak hitting -20.8°C. More typically though, only about one-third of recent Aprils had any Lows which hit -10°C.

We almost certainly haven't seen the end of the snow though, because in April and May we average another 15cm and 6cm of snow respectively.

2021/03/28

Zero Snowdepth for 2021

This is a little late, because after a warm start to March things have cooled off a bit, and that threw some uncertainty into the question of whether our snow has officially melted or not.


2020-2021 Snowdepth
In this chart the blue and orange lines are the snowdepth for the winter of 2020-2021 for Blatchford and the International respectively. The light blue stuff in the background shows the average and the range of snowdepths at the International over the past 30 years.

Blatchford's final recorded snowdepth this winter was on March 9th at 3cm, and after that snowdepth has been blank. The International hit 2cm on March 17th, and it hung out there until March 20th. On the 21st it had no meausurement, and since then it has been showing "Trace" amounts of snow on the ground. "Trace" doesn't mean 0cm, but it's close, and eventually it will disappear.

For the winter as a whole both stations jumped to well above average in early-November, and then were mostly flat through mid-February. Things started to drop in the last week of February, and then really fell off a cliff in the first week of March.


2020-2021 Snowdepth - Outlying Areas
For a bit more context, here the snowdepths for Stony Plain and Campsie (about 100km NW of Edmonton) are also shown.

Snowdepth seems to be Environment Canada's least precise measurement, but the Stony Plain and Campsie stations had less snowdepth for most of the winter than the two main Edmonton stations did. Stony Plain's snow disappeared about a week before Blatchford on March 2nd. For Campsie it was March 15th, which was a week after Blatchford and a week before the International.


Recent Winters
This chart has the history of snowdepths and melts for recent winters.

March 21st is pretty early for all of these stations to be snow-free, although 2015 and 2016 were both about a week earlier. But comparied to years like 2020, 2018 and 2013 this winter was about a month ahead.

People always like to joke about "second winter," and just because all of the snow has melted that doesn't mean that we won't get more. In April and May we average another 20cm of new snow, but looking at the snowdepths here that late-spring snow usually doesn't have much of an impact on the ground. 2015 and 2016 both had early melts, which were followed by another week of snow in late-March. And winters like 2017 and 2014 had fairly late melts, and after that the snow showed up again for another week in mid-late April.


Lasting Snow
In this chart each of the narrow blobs shows the length of time for which there was snow on the ground during each winter.

For the winter of 2020-2021 Blatchford had snow on the ground for 122 days in-a-row. That was from and early~ish start on November 8th through to the early finish on March 9th. In recent years 2019-2020 went 141 days and 2017-2018 went 170, while 2014-2015 went 95.

The International had measureable snow on the ground (we ignore the "trace" amounts in the chart) for 133 days, from November 8th through March 20th. 133 days is pretty low for the International: 2016-2017 went 134, 2015-2016 went 121, 2014-2015 went 126. For longer winters recently 2019-2020 was up at 169 days, with 2017-2018 at 172.