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Is our October snowfall a predictor of winter?

In winters following October snows, the odds favour near- to above-average precipitation

With what seems to be an early attempt by winter at moving in, I am already beginning to hear people talking about just what this means for the upcoming winter. One of the biggest questions I hear is, “When are we going to get snow that will stay?” or, “I hear the normal time to get snow is November (date here)?” You fill in the blank, as everyone seems to have a different date! The conversations also usually include comments about how unusual it is for us to see snow in October. Every year or two, I like to re-examine this topic, trying to dig a little deeper into it each time. This year we’re going to take a look at the dates for the start of winter across southern and central Manitoba. Then we’ll take a quick look at just how often we have seen October snowfalls, and see if there is any correlation in those years with what the following winter was like.

As we’ve been learning over the years, certain weather-related questions sound simple enough, but when you actually start to look at the question it becomes tougher to figure out. The tough part about trying to figure out when winter begins is how to define just what constitutes the start of winter! Should it be the first significant snowfall? How about when the high temperature consistently stays below 0 C, or should we simply use the astronomical date of Dec. 21, or maybe just stick to the meteorological date of Dec. 1?

I think most people would agree that winter doesn’t really arrive until you have snow on the ground, so for us, I use this as our measure of when winter arrives. Even narrowing it down to this still has some problems. Take this year, for example. A good portion of agricultural Manitoba received measurable snowfall earlier this month. While the snow in the harder-hit areas stayed around for a day or two, by Oct. 8 it had pretty much all melted away. So now the question is, did winter arrive in early October, or should we call this a false start to winter? For me, if the snow melted and is gone for more than a couple of days, I would say that it was a false start to winter and that the true start date won’t happen until it snows again and then sticks around.

With this in mind, I double-checked the snowfall records for Winnipeg, Brandon and Dauphin and came up with the dates in Table 1 (below) for when we should expect winter to officially start.

From Table 1 we can see that all three regions of agricultural Manitoba have seen winter begin in October and as late as mid-December. Winnipeg and Brandon both have an average date for snow to stick around of Nov. 14, with Dauphin four days earlier at Nov. 10. The “usual range” is a measure of the standard deviation around the average. It indicates the range of days that we should expect winter to begin. If winter begins before or after these dates, it is a very unusual year.

Next on the list is just how rare or unusual October snowfalls are. I looked at data for both Brandon and Winnipeg, and interestingly, both stations reported about the same probability of seeing measurable snowfall in October. Both stations have seen about 36 years with measurable snowfall since 1936. This works out to be about a 43 per cent chance of seeing snow. This does not take into account the total number of October snowfalls that have occurred, but simply how many years have reported any measurable snowfall. If we look at years that reported a snowfall of more than two cm in October, there have been at least 12 years over the last 83 years where October reported more than one two-plus-cm snowfall, or about 14 per cent of the time.

For the next part of this investigation, I used just Winnipeg’s data. I looked back at all the years that reported October snowfalls and then looked at the average winter temperature and total snowfall. Table 2 shows how those winters turned out.

Looking at Table 2 (below), the highest probability is for near-average temperatures with near- to above-average amounts of precipitation. I did notice, as I went quickly through each year’s data, that a number of the winters saw big swings between warm and cold months and wet and dry months. So while the winter as a whole may have been average, some of the months in those winters were very wintry with a lot of snow, and other months were nice and dry. With the current long-range weather models continuing to show warmer weather moving back in by November, it will be interesting to see if this up-and-down winter pattern develops this year.

About the author

Co-operator contributor

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.

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