Warm westerly winds that began Monday evening continued into Tuesday, raising morning temperatures in many southern Alberta communities.

At 6 a.m., it was already 9°C in Calgary, compared to a normal overnight low of -12°C.

Westerly winds are expected to peak at around 30 km/h in Calgary Tuesday morning with gusts closer to 50 km/h, but a leeward trough will interrupt this trend early in the afternoon.

A lee trough is a low pressure system that forms on the leeward side of a mountain range, or in this case, the Alberta side of the Rockies.

This low will become a classic Alberta “clipper” – a rapidly developing weather system associated with unsettled conditions in eastern and southern Alberta.

Colder air will mix with precipitation overnight Tuesday and morning travel across southern Alberta on Wednesday may include freezing drizzle and/or fog.

This disturbance will be brief with a return of warmer air on Thursday and will continue until Saturday.

With sunshine most of the time and the increased evaporative qualities of a westerly flow, a freeze-thaw cycle will appear in Calgary, meaning sidewalks and parking lots will likely become icy overnight.