Interestingly enough, it was about this time last year that I was in the process of writing a very similar article to what I’m writing now. The eastern Prairies have seen a fairly warm fall so far this year, with average temperatures during the first two weeks of September around 2 C above the long-term average. Over western regions it has been even warmer, with temperatures over much of Alberta averaging a good 4 C warmer than the long-term average so far this month.
Last year we also saw a really nice first half of September before the bottom dropped out in the middle of the month, at least for everyone except southern Alberta. Here is a clip from the article I wrote last September:
“The cold weather moved into Alberta first, with the northern areas seeing low temperatures in the -1 C to -3 C range on the morning of Sept. 12. Southern regions fared better and escaped the frost, with overnight lows only falling to around 3 C. This cold air mass then moved into Saskatchewan, where on the morning of Sept. 13, the overnight lows dropped below freezing for the first time this fall across most regions. The following night the bottom really fell out, as several locations recorded temperatures as low as -6 C. Around this same time the cold air moved into Manitoba, but slightly higher wind speeds combined with a few more clouds, kept the temperatures slightly warmer. Overnight lows on the 13th and 14th did fall below freezing in most regions, though, with the coldest readings coming in around -3 C.”
Well, this year isn’t an exact copy of last year, but frost has already made an appearance in a few locations across the Prairies and it looks as though the eastern Prairies are going to follow last year’s pattern. A deep trough of low pressure looks to be developing over east-central North America during the next week or so. Out west it looks like some regions will experience a taste of Indian summer, as a ridge of high pressure builds over the West Coast.
Each year I usually discuss this unique topic. Some people say that simply using the term Indian summer is politically incorrect and that I should come up with another term. While the term Indian summer has some fairly uncertain origins, the earliest reference found in the literature dates back to Jan. 17, 1778, when the farmer and author St. Jean de Crevecoeur wrote in a letter:
“Sometimes the rain is followed by an interval of calm and warmth which is called the Indian summer; its characteristics are a tranquil atmosphere and general smokiness. Up to this epoch the approaches of winter are doubtful; it arrives about the middle of November, although snows and brief freezes often occur long before that date.” The fact that de Crevecoeur stated that this was called “Indian summer” suggests that this term must have been in use before that time.
I have never been a fan of political correctness just to be politically correct and I personally don’t see an issue with this term, but if you think there is a better way to describe what most people consider the best part of fall, feel free to let me know.
So just what is considered Indian summer? It’s defined by a particular set of criteria, which should help us to determine when it is occurring. It’s generally accepted that for Indian summer to occur, the following conditions must be met:
1. There needs to have been a hard or killing frost.
2. Mostly clear skies (or perhaps local fog at night).
3. No precipitation.
4. Light winds and generally calm nights.
5. Daytime maximum temperatures greater than 18 C.
6. Nighttime minimum temperatures staying above freezing.
7. Conditions lasting for at least three days. (Keith C. Heidorn)
Most regions on the Prairies have now seen at least one hard frost, so now we have to wait to see if the rest of the criteria can be met. Points 2 to 6 are usually not that hard to meet. Those of us who follow the weather across the Prairies know it can be tough for Point 7 to happen.
The best chance over the next couple of weeks looks to be over the west in Alberta. It looks like those of you over the eastern Prairies will have to deal with some cold fall weather, at least for a little while. But there is still plenty of fall left — and let’s hope that the nice weather out west continues and spreads east for October.