Today we're going to continue on that topic, and look at when our snow usually starts to disappear.
It's a funny thing to talk about today, since all of this winter's snow is basically already gone. But even in a normal year, the start of the big melt would usually be just around the corner.
Average Snowdepth
This chart is something that we looked at last week, and it shows the average snowdepth during the winter, along with the recent quartiles, highs and lows.
In 2016-2017 we've already had a few melts, which isn't particularly unusual. What is a little unusual, is that because we had so little snow to begin with, last week's very warm temperatures dropped the airport all the way down to 2cm. And right now the downtown has been basically snowfree for a few days.
Low-Snow Winters
The speed of the yearly melt is obviously going to depend on how much snow we start with, so here are the 5 years with the lowest maximum snowdepth, going back to 1995. The winter of 2016-2017 isn't over yet, but I've included it here because so far we maxed out at 18cm back in January.
2000-2001 was by far the least snowy winter in recent memory, with the snowdepth never rising above 7cm. After that we have last year's non-winter, which reached 17cm in late-January, 1997-1998 comes it at 20cm, and 2001-2002 was at 25cm. After that, the next 7 years which aren't shown on this chart all topped-out between 26cm and 30cm. So a maximum snowdepth of between 25cm-30cm is actually pretty common.
Snowy Winters
The flipside of the low-snow years is the really snowy ones, and here we have the 5 winters (6 actually, since there's a tie) since 1995 with the greatest recorded snowdepth.
Our 5 low-snow winters ranged from 7-25cm, and these 5 snowy winters are between 44-53cm.
Our last two winters 2015-2016 and 2016-2017 have (so far) been very low, but in recent years 2010-2011, 2012-2013 and 2013-2014 were all in the Top 5. 2012-2013 was actually quite low for most of the winter, until a late-March storm pushed it up to 49cm for a week or two.
The Earliest Melt
So when does the snow finally disappear? Here we have the snowdepths just from March onward, and we're looking for the point where all of the snow that built up over the winter is gone.
Last winter the snowdepth first hit 0cm on March 13, which made 2015-2016 the earliest melt going back to 1995. Right after that it snowed again, but here we're just interested in when the snow first disappears. That might seem like a bit of a cheat, but we can see here that the late-spring snows don't usually hang around for more than a few days.
Keeping that assumption in mind then, 2014-2015 was the second earliest to hit 0, on March 28. And in 3rd place is our low-snow year 2000-2001, on March 31.
The years with the slowest or latest melts were 2010-2011, 2001-2002 and 2012-2013 all stretching until the last week of April.
Here's another version of the same chart, this time highlighting the actual drop. We can see that for the most part we hit 0cm around the first or second week of April - although there are a few early years and a few late years.
I usually think of melting as being a gradual process, where most of the snow will disappear quickly, but some remnants will seemingly hang around for weeks. We don't really see that here, because once things start they pretty much all head straight down to 0 (although a few years bounce up a bit from new snowstorms).
It is worth remembering though, that this is Environment Canada's snowdepth for the International Airport. In the real world there are probably patches of snow in the shade that hang around a bit longer than what we're seeing here.
When Snowdepth Reaches 0cm
If we look at the "average" day that the snow disappears, it's right around April 15th. Although more typically that means it fluctuates between the beginning and the end of April. And once again I'm surprised to see the late-80s/early-90s were consistently earlier than what we've seen recently - by about two whole weeks.
March Surprises
Today I've been talking about winter like it's already over, but that isn't necessarily the case:
In March through May we typically get about a quarter or a third of our total snowfall for the year, and here are a few winters which saw significant increases in snowdepth in either late-February or March. One thing that we can see from these late snows is that they don't usually last very long. These big jumps all disappear within a week or two.
The two most interesting winters here are probably 2011-2012 and 2005-2006. They both had really low snowdepth at the end of February, before some big storms pushed things way up, and extended their melts by a few weeks:
Snowdepth on February 20th
Here we have the snowdepths for each year, as of February 20th. Right now we're at 2cm, which puts 2017 in 3rd-lowest place overall after 1991 and 2006 which were both near 0cm.
At this point of the year 2012 was just a little bit higher at 4cm, before getting a tonne of new snow which pushed the snowdepth up by 25cm. And 2006 was basically at 0cm for the whole winter, before being buried under snow during March. So who knows what this spring will bring?
As we approach the end of February though, what we do know is:
- the big melt will probably get started in a week or two
- a few weeks after that it will be in full swing (assuming that there's still any snow left at that point)
- in a typical year the airport would be completely snowfree in maybe another month-and-a-half
Right now the downtown is already basically snowfree. There is still snow in the parks and open areas, but anything that is close to a building or road is clear. So I'll be watching for when the airport's numbers officially hit 0cm, to compare that to what we see downtown, in the parks, and on the singletrack.
No comments:
Post a Comment