Western Manitoba was once again hit with significant rains late last week as a strong but luckily fast-moving Colorado low lifted almost due north through this region, bringing some heavy rain and thunderstorms. The table shows some of the rainfall totals as compiled by Environment Canada.
While the low did bring significant rains to this region it also brought some very warm weather to nearly all areas, which leads to my main topic for this issue. Every year or two I receive an email asking about Indian summer: just what is it, and how do we know when we are experiencing it? Well… let’s take a look!
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 this description is actually not that bad — but that is 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 is occurring. It is generally accepted that for Indian summer to occur, the following conditions must be met:
- There needs to have been a hard or killing frost.
- Mostly clear skies (or perhaps local fog at night).
- No precipitation.
- Light winds and generally calm nights.
- Daytime maximum temperatures greater than 18 C.
- Nighttime minimum temperatures staying above freezing.
- Conditions lasting for at least three days. (Keith C. Heidorn)
Most regions saw killing frosts on Oct. 5 and 6, followed up by mostly clear skies and warm temperatures on Oct. 8 through to Oct. 12. Eastern regions saw the warmest, sunniest and driest conditions while the far west saw clouds and rain move in on the 11th. With temperatures topping out in the low 20s, we definitely saw highs greater than 18 C, and overnight lows were fairly mild, staying well above freezing. So it definitely looks like we hit all of the criteria for last week’s weather to be called Indian summer.
“Wondrous second wind”
The term Indian summer has some fairly uncertain origins. The earliest reference found in the literature dates back to Jan. 17, 1778, when J.H. St-John 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 this was called Indian summer suggests 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.
As I wrap up this look at Indian summer, I think it’s 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, Walt Whitman’s Diary in Canada, 1904.