The amazing summer weather that dominated the Prairies during the first week or so of September came to a freezing end by the middle of the month, as a strong area of Arctic high pressure brought the growing season to a close. After seeing record-high temperatures in many places across Manitoba, Saskatchewan and Alberta during the seven-day period from September 4 to 10, anyone following the weather knew that we were likely in for some cold weather. That said, I don t think anyone would have predicted that we d go from record-high to recordlow temperatures in just a couple of days, but that s exactly what happened.
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.
So it appears that everyone except southern Alberta has now experienced a killer frost, and if the weather models hold true, it looks like we ll be in for beautiful Indian summer weather over the next couple of weeks.
Just what is Indian summer? The most common response that I receive 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 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 our region, Indian summer seems to be defined by the following set of criteria:
” 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.
For most regions we have seen the hard or killing frost, which means that we just need to hit the six other remaining criteria. The current medium-to long-range forecast is showing a large ridge of high pressure building across the Prairies. This should bring a prolonged period of clear skies (point No. 2). This ridge should keep any storm systems away, and it doesn t look like thunderstorms will be in the cards, so that takes care of point No. 3. Should this ridge of high pressure develop as forecast, it is looking very similar to the ridge that brought the sunny hot weather early this month. The ridge also brought relatively light winds, so we should be able to cover off point No. 4. It s also looking like temperatures will be unseasonably warm during this period, with highs running as much as 6 to 10 C about average (points 5 and 6). Finally, the models show this ridge sticking around for at least a week and maybe much longer, so point No. 7 should not be an issue.
I guess the next question is, what will happen once this Indian summer is over? Well, I wouldn t be surprised if we see another shot of cold air invade the Prairies, and we might even see a few more recordlow temperatures. Overall, though, I personally believe that we haven t seen the end to warm fall weather just yet, and there just might be another ridge of high pressure in our future sometime in October.