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Fall: A season of weather extremes


By Rob Davis
Meteorologist
@RobDavis_Wx
Wednesday, September 11, 2013, 7:31

I don’t know about you, but I’m not ready to say goodbye to summer.

The fall season is getting underway in Canada. At this time of year, every day is 3 to 4 minutes shorter than the day before. Temperatures are starting to drop, and sweaters & hoodies are starting to come out of storage. The inevitable is happening: summer weather is almost gone. 

But here in Canada, seasons don’t tend to turn off for good. Fall is known as a transition season, and for good reason. During the fall season, both summer and winter can infiltrate. Sometimes they can both make an appearance within the same week. So how long can we fool ourselves? When must we accept that summer is finally gone? And just how early can those early signs of winter show up? 

Looking through the historical records, the fall season is full of weather extremes. Let’s take a look at some of the latest summer-like days, and the earliest winter-like days, to ever occur.

ATLANTIC CANADA

Residents of Atlantic Canada can hold onto a good chance of a few more summer-like days over the next month or so. A 20-degree day has been known to occur as late as Hallowe'en in most of The Maritimes, and can even happen through late November in parts of New Brunswick.

But the harsh reality is, winter just isn't that far away. And when looking at the numbers, it can appear much sooner than you might think. Temperatures can start dipping below zero early in the season, and can reach below -10°C as early as late October for some.

Even more striking: At some point in history, almost every town in Atlantic Canada has seen a double-digit snowfall in mid-October.



QUEBEC

Quebec takes full advantage of both summer weather and winter weather. And it’s no surprise why: Quebec is well-acquainted with both seasons.

During the fall season, summer can linger well into October. But on the flip-side, winter can make its first appearance in the same month.

To put it in perspective, Montreal’s latest 25-degree day on record was on October 22, 1979. But the city’s earliest 10 cm snowfall ever measured was almost two weeks earlier in the year! It snowed 15 cm on October 9, 1888.



ONTARIO

Ontario is a BIG province. A few times a year, the weather in Toronto vs. Thunder Bay can be so different, that it's hard to imagine them within the same provincial borders. This is especially true in the fall months, where summer and winter conditions can occur within Ontario at the same time.

Southern Ontario

Compared to most areas of the country, southern Ontario during the fall season ain't half bad. Temperatures can reach into the 20-somethings through most of November. If lucky, it can even hit 30°C during early October. The most recent occurrence of this was Thanksgiving Day 2007, where most of Southern Ontario surpassed the 30-degree mark.

Temperatures eventually drop into the negative numbers, sometimes as early as mid-September. But the biggest shock to the system is arguably that first sighting of snow.

How early can it snow in Toronto? Surely it’s not until November, right? Well, this may come as a surprise to many Torontonians, but the earliest appearance of snow in Toronto’s history was on October 1st. In 1920, almost a centimeter of wet snow fell in downtown Toronto. And if that’s not shocking enough, double-digit snowfalls are possible by late October. Looking back at history, 12 cm of snow fell on the city on the night of October 21, 1969.



Northern Ontario

Northern and central Ontario are not as lucky as their southern counterpart. While warm temperatures can make several appearances through the early-to-mid fall season, words like "minus" and "snow" become part of the vocabulary as early as mid-September. Most cities in northern Ontario have hit below -10°C at some point in their history by mid-October.



SASKATCHEWAN AND MANITOBA

Fall is truly a transition season in the eastern Prairies, but it's not a subtle transition by any means.

Temperatures can rise above 30°C well into October, and yet double-digit snowfalls have been seen several times in the past during September.



ALBERTA

Alberta takes the prize for the most roller-coaster weather during the fall months. As any Albertan can attest to, it's not uncommon to experience summer-like and winter-like weather in the same week during the fall. And the numbers show the same thing.

Calgary may hold the record for the wildest week of temperatures in Canada’s history. On the morning of October 24, 1887, temperatures plunged to a frigid -22°C (the earliest -20°C ever recorded in Calgary). Just five days later, on October 29th, it hit 25°C (the latest 25°C in Calgary’s recorded history). That’s a 47 degree temperature swing in just 5 days!

Edmonton has some equally shocking stats. The city can reach 20°C as late as November, and hit -10°C as early as September. And speaking of September, Edmonton can be ankles deep in snow by mid-month. In 1926, 22 cm of snow fell on Edmonton over two days during mid-September.



BRITISH COLUMBIA

British Columbia’s weather extremes during the fall months may be a bit more extreme then you may have thought.

Summer weather tends to gradually fade away in British Columbia, with the last sign of 20-degree days occurring as late as early November.

But it’s the winter weather extremes that may surprise many. For example, double-digit snowfalls have once hit both Vancouver and Victoria during early November. In the B.C. interior, major cities have seen snow as early as mid-October.

Equally as surprising, cold snaps can strike by late-October in the interior, and by mid-November along the coast and island.



NORTHERN CANADA

Canada’s territories have quite the dynamic climate, thanks to the drastically changing length of days that occur between summer and winter. Winter is not a year-round phenomenon for Canada’s north, but it does set in early. Most areas can expect a taste of winter as early as late September.


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