There are different dates for when the seasons begin. Meteorological autumn begins in September 1, immediately after the end of the three warmest (on average) months. According to my calendar, the fall season this year begins on September 22 at 22:29 EDT .
The earlier date is more accurate this year, at least for people in Alberta who have experienced two serious snowstorms earlier this month, and those further north in Ontario. Snow in the past day or two in Armstrong, Geraldton, and other communities in the north probably has the locals convinced that the fall season is already underway.
Light frost, and killing frost in a few locations, is another confirmation of seasonal change. We can see some colour in trees and forests already in Thunder Bay and the northern Midwest. Some maple and sumac have hints of red and other hardwoods are showing previews of the changing of the leaves. It is more apparent north of Lake Superior.
Weather is a most critical item in the timing of what we see displayed every fall, although diminishing daylight plays a role too. A few factors contribute to premature displays. Some individual or stands of trees can start early because of moisture deficiency and other triggers. A cool and wet summer can also trigger changing of the leaves well before frost. The most vivid colours tend to follow warm summers with sufficient moisture followed by sunny but cool autumn days. Light frost accelerates the process but a switch to very cold mornings will often end the colourful season fairly quickly.
An Indian Summer?
Typically, the confirmations of the fall season – frost and minor snow amounts – are followed by a return to warmer conditions. Such conditions appear very likely in the western half of North America for the rest of September. The dividing line between much warmer than seasonal and normal or cooler-than-normal is likely to fall through Northern Ontario and the upper Midwest. Precisely where the line happens will define both the warmth and duration of Indian Summer.
I have garden harvesting on my agenda and am hoping for warmer conditions but, let’s be realistic – a return to seasonal conditions after the next very cool day or two is more likely.