We have had some nice Indian summers in the past, but the weather we experienced over the last week, and especially over the long weekend, was probably one of the best textbook examples of Indian summer that I have ever seen. A couple of years ago I wrote an article about Indian summer and I thought we should take another look at just what an Indian summer is. Then I’ll take some time to look back and see when we last saw this kind of summer-like weather in October.
First of all, I think the main question is “Just what defines an Indian summer?” The most common response I hear or see is that Indian summer is a period of warm weather that occurs sometime in late September or October. After researching the details of Indian summer, I found that this description is actually not that bad, but that’s the problem with the term “Indian summer.” There just doesn’t seem to be a set definition. The definition of Indian summer appears to be set by the geographical region rather than by a definite set of criteria, with different areas of North America defining Indian summer a little bit differently.
For the area of the Great Plains and the Prairies of Canada, Indian summer is defined by a particular set of criteria, which should help us to determine when it occurs. It’s generally accepted that for Indian summer to occur. the following conditions (courtesy Keith C. Heidorn) must be met:
There needs to have been a hard or killing frost: Check.
Mostly clear skies (or perhaps local fog at night): Check.
No precipitation: Check.
Light winds and generally calm nights: Check.
Daytime maximum temperatures greater than 18 C: Check.
Nighttime minimum temperatures staying above freezing: Check.
Conditions lasting for at least three days: Check.
If we accept these seven conditions as being the indicator that Indian summer is occurring, then there is no doubt we’ve been experiencing it!
The term “Indian summer” has some fairly uncertain origins. The earliest reference found in the literature dates back to Jan. 17, 1778, when St. John de Crevecouer 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 Crevecouer stated that this was called “Indian summer” suggests that this term must have been in use before this time.
The meteorological conditions behind Indian summer usually involve an area of high pressure building into our region in late September or October, which is exactly what happened this year. A fairly strong ridge of high pressure in the upper atmosphere built over western North America early in October and that, combined with a strong area of surface high pressure, brought most of southern and central regions of Manitoba the incredible weather we have seen so far this month. In fact, over the first 11 days of October we have seen eight days in a row with high temperatures at or above 20 C. The last time we saw this many days above 20 C in October was way back in 1963.
October 1963 was a truly remarkable month. It holds the record for the warmest October, with a mean average temperature coming in around 11 C, about 6 C above the long-term average. To put this into perspective, the 11 C mean temperature for that October would be about average for September. While the average temperature for this month was record breaking, even more impressive was the number of days that saw high temperatures warmer than 20 C. During that momentous month, our region experienced a total of 16 days with high temperatures warmer than 20 C. While we have seen a remarkable streak of eight days in a row with high temperatures over 20 C, October 1963 saw a streak of 11 days in a row that began on Oct. 8 and lasted right through to the 18th of the month.
While we still have over half of October left to us this year, I really doubt we’ll break the 1963 records. As we move further and further into October it gets harder and harder to break the 20 C mark, but I guess you never know. So, as I wrap up this look at Indian summer, I think it is appropriate to conclude with Walt Whitman’s perfect quote about it.
“It is only here in large portions of
Canada that wondrous second wind, the Indian summer, attains its amplitude and heavenly perfection, – the temperatures, the sunny haze; the mellow, rich, delicate, almost flavoured air: Enough to live – enough to merely be.”
– WALT WHITMAN