It has been kind of interesting watching the weather models over the last couple of weeks. They keep trying to forecast cold air pushing south, but areas of low pressure seem to keep developing to our southwest and west. The counter-clockwise rotation around these lows stalls the southward progression of the cold air as warm air is forced northward. We saw this last weekend as temperatures soared into the mid- to upper 20s. The question for this forecast period is whether this pattern will continue — or will the cold air finally spill southward, bringing the first frost of the season?
The latest forecast model at the time of writing leans toward a continuation of this pattern, with a possible amplification toward even warmer conditions. This forecast period will begin with a brief shot of cool air dropping southward behind the area of low pressure that should have brought some showers to southern and eastern regions earlier in the week. It does not look like there will be any frost, but at this time of the year you never know. Mild air will quickly move back in by Thursday as an area of low pressure builds to our west and tracks by well to our north. Mild air looks to stick around until at least Friday before a second area of low pressure zips through the central Prairies.
This second low may bring the odd shower sometime on Friday. Cooler air will try to work its way in behind this low over the weekend, but the models show another area of low pressure digging to our west which will help to amplify a ridge of high pressure just to its east. This building ridge and the southerly flow ahead of the low will help temperatures moderate over the weekend and into the early part of the last week of September. Expect daytime highs to climb into the low to possibly mid-20s by Sept. 29, with overnight lows falling to around 10 C or a little cooler in some areas.
Usual temperature range for this period: Highs, 12 to 22 C; lows, 1 to 10 C.