Most of central and southern Alberta will experience one more day of unusually warm temperatures before a very cold air mass starts to move in.
A large and strong ridge of high pressure that sat parked along the eastern Pacific basin over the past few days will start to break down Wednesday, likely amplifying onshore winds for a good portion of the west before opening up a path for polar air to flood across most of North America by the weekend.
By Thursday wind gusts in southern Alberta, including Crowsnest Pass, could reach warning thresholds, peaking at 100 km/h.
Along the northern edge of that ridge and in the space where that warmer air will encounters the incoming colder air, instability is expected to intensify.
Snowfall warnings have already been issued for the southern Northwest Territories, northern British Columbia, northern Alberta and north and central Saskatchewan in anticipation of heavy accumulations of snow (15 to 25 centimetres) from Wednesday until Thursday
Lightning is possible as the low pressure system starts to track south and the trough deepens.
Central and southern Alberta, which sit along the southern edge of the incoming northern low might also see some snow on Thursday and Friday.
Polar air will produce unusually cold temperatures and dangerous windchill values across most of central Canada by Sunday.
A low-riding jet will support widespread sub-zero temperatures to extend as far south as the central and southern United States as well, which will prove problematic in some areas where homes and vehicles are ill-equipped for such extremes.
In Calgary, the daytime highs which will be 12 degrees above seasonal on Wednesday, will drop to -16 C by Sunday, sitting just below the average overnight low value of -15 C.
This pattern will be relatively short-lived for southern Alberta, with daytime highs in Calgary climbing back up to 2 C by Tuesday.
