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.

July 2016 Rainfall

The rain was in the news a lot last month, with what seemed like constant thunderstorm watches, and the emergency canoes were even called out a few times to save people from the flooded Whitemud.

So it seemed like a really rainy July, but was it? It depends a bit on exactly where you were:

The chart shows the cumulative rainfall totals for four of the stations around Edmonton:

• International Airport - 102mm
• Blatchford - 88mm
• UofA - 86.2mm (unfortunately data is missing for the final 4 days)
• Stony Plain - 69.6mm

The totals for the month vary by station, but we can also see that different stations got hit on different days. The International received more rain right at the beginning and the end of the month than the other stations, but the big storm on the 26th mostly missed it.

That storm on the 26th was the first of the Whitemud floods this year, and at least one local weather station recorded 60mm in just a few hours. None of these Environment Canada stations show anything quite that significant though, with the largest one-day rainfall recorded as 39mm on July 30 at the International Airport.

So rainfall definitely varies by location, but for the rest of today I'm just going to stick with the International. Of these four stations it had the highest numbers (excluding the UofA and its missing data), and it's the station that I have all the historic charts setup for.

In terms of number of rainy days, this year was a little above the average with 17 days of recorded rainfall. The 20-year average is 15, but the maximum was 23 in 1996, so this year was quite typical.

Anecdotally, I have a four year old dog who hates thunder, and this year broke her brain. She's lived through three mostly quiet summers, but this July's night-after-night thunder sent her scurrying to hide in the bathroom most evenings.

In terms of amount of rain, the 102mm at the International put us just a little bit above the average, and just a little below this year's total for May.

And this chart compares July rainfall totals for each year going back to 1985. Each column is divided by week to give a sense of roughly when the rain fell. And 2016 is right inline with 2012-2015, and below 2010 and 2011.

For a truly rainy July, we can take a look at Calgary:

This is the same chart as the previous one, but with a line added to show the rainfall for the Calgary International. Normally Calgary gets less rain in July than Edmonton does - in 22 of the last 30 years Edmonton has had more, and Edmonton averages 93mm compared to 69mm in Calgary.

But in July 2016 Calgary received 206mm of rain, which doubled Edmonton's numbers, and tripled their average. Prior to 2016, their rainiest July in the last 30 years had only had 133mm of rainfall. So Calgary definitely had a rainy July this year - and in comparison Edmonton's was very average.

Finally, here's where Edmonton's total precipitation for the year sits. The May long weekend pushed us up above average, and since then we've tracked pretty closely along the average line. Then right at the end of July the International got a few big storms to boost things up a bit more.

136ish Years of Precipitation

Last winter I looked at Edmonton's entire 136-Year recorded history of warm winter days, and cold winter days. Today I'm going to look at Edmonton's precipitation history, but it's a little trickier because of the data that is available. Rather than 136 years, it's more like 136-9+55 years worth of precipitation.

I've mentioned before that the precipitation data for the Edmonton Blatchford weather station isn't good, and here is the problem:

Environment Canada makes note of any days that have missing measurements, and from 1881 through 2006 things went pretty well. But in 2007 there were 31 days with missing precipitation data. In 2008 through 2013, each of those years had more than 200 days with missing measurements. And finally, in 2014 all 365 days are missing. Then 2015 dropped to a more reasonable 89, and so far in 2016 there has only been 1.

I'm not sure what caused this - why after more than a century of record keeping would you just take a little break? One might think that the closure of the airport had something to do with it, but the vote to close the airport wasn't until 2009, and the first runway closure was in 2010. The Edmonton Indy might seem to be another possible factor, but it started earlier in 2005 and lasted through to 2012.

So I don't know what caused the gaps in the data. I just know that they are there.

Those gaps mean that the Blatchford data can't be used for any current comparisons, or trends, or averages. But there is still more that a century of data to look at.

For the missing recent history the Edmonton International Airport is available as an alternative, although it only has data back to 1961:

This is a comparison of the Edmonton International and Blatchford, and the purple line along the bottom is the difference between the two stations each year.

From 1961 through 1995 the two stations were within +/-75mm of each other every year, which is about 20%. But then in 1995 the Blatchford numbers started to drop off, and in 2000 the difference between the two stations peaked at 218mm. Precipitation is much more local than temperatures, and it's possible that the International received a few big storms that the downtown didn't. But 451mm at the International vs 233mm at Blatchford is pretty huge (almost 50%, and over 3 standard deviations from the mean). 

Knowing the problems with the 2007-2015 Blatchford data, this does make me wonder if maybe there are some unreported errors in the 1995-2000 era? But I'll come back to that in a bit. For now, lets just take a closer look at the Blatchford data:

I'd tried to add a trendline to the Blatchford data, but it wasn't very interesting, so it isn't shown. Things are low at the beginning, low at the end, and flat in the middle, so the trend for the century just looks flat.

So instead of a trendline here is the 5-Year moving average, which removes some of the year-to-year noisiness. And for almost a century - from about 1905 through 1995 - that average fluctuated back and forth in the range of 400-535mm per year.

I tend to think of the 1930's as a time of extreme drought, because of all of the photos of the dustbowl and the stories of the depression. But at least for Edmonton that is a little hard to spot in the data. 1929 was low, and 1930 was very low at just above 300mm (making it the 8th lowest year). But after 1930 the precipitation quickly recovered, even if the economy didn't. And the lows of the early 1930s are pretty comparable to the early 1920s, early 1950s and much of the 1960s.

The only times that the average broke out of the 400-535mm band were at the beginning and the end of the century. 1900 and 1901 both had about 60% more precipitation than the 20th century average. And then the late 1800s and early 2000s had some years that were as low as half the average.

Here is the Edmonton International data, with the same 400-535mm range shaded in. And we can see that for the most part the International stays within that band as well.

Unfortunately there isn't a lot of overlap in the highest and lowest years for the two stations, mostly because many of Blatchford's extremes were a century ago. But one thing that is common between the two charts is 2002, which had the lowest recorded precipitation for both Blatchford and for the International. Even though it is the lowest at both stations, there is still a significant difference in the measurements, with Blatchford at 188mm and the International at 267mm.

Last year a state of agricultural emergency was declared, because there had been so little precipitation. But based on the numbers for the International, 2015 still had 40% more precipitation than 2002. On the other hand though, looking at the 5-Year average we have now had a string of relatively dry years, and the last year with a lot of precipitation was all the way back in 1996. For about the last 15 years the average has been sitting at the bottom of that 400-535mm range.

And that brings us back to the Blatchford data. From 2000 onwards the precipitation at the International is fairly low, but at Blatchford it absolutely nosedived. Which one is right? Or are they both right? It's time to look at some other stations for comparison.

Edmonton has other stations with precipitation data, and two of them - the University of Alberta Metabolic Centre, and Stony Plain - are shown here.

This is a very busy chart, and I won't look at it in too much detail - Stony Plain tends to be a little higher than the other stations, taking top spot in 18 of the 31 years shown here; and all 4 stations show a downward trend since the mid-80s.

The main point of interest here is the years from about 1995-2002, where the Blatchford data is significantly lower than all three of the other stations. Precipitation is local, but I'm suspicious that Blatchford really only received half as much precipitation as the University did in 2000. So I already know that Blatchford's 2007-2015 data has problems, but I think that 1995-2002 looks pretty dubious as well.

I've previously said that I don't like the recent Blatchford precipitation data, and this confirms that. It's still interesting for some historic records, but in the future I'll continue to use the International whenever I'm looking at recent precipitation.

One final thing for today:

Environment Canada records the totals for rain and for snow, and they are shown in the graph above. This is the mm-equivalent of melted snow. If I used the freshly fallen unmelted snow the numbers are 10x as much, but that distorts the graph. Next winter I will definitely take a closer look at Edmonton's snowfall. But for now, this gives a sense of roughly how much of our yearly precipitation comes from snow or rain - for snow the average is 120mm versus 330mm for rain.

Update: I've reworked some of these charts using a different Blatchford dataset, which gives less suspicious results for the 1995-2005 period. The update can be found here.