A very stable weather pattern has developed over the western prairies bringing persistent warmth to the region. Warm Pacific air is pouring into the southern half of B.C. and Alberta due in part to some well-positioned low-pressure systems north and south of this zonal flow. On Friday, the daytime high in Calgary will reach 22 C, and that will be the coolest high until Tuesday. Overnight values in Calgary are expected to range from 7 C to 10 C until next Friday, compared to the normal low temperature of 4 C. There will be little to no cloud cover for at least a few days with this synoptic setup and wind speeds north of the southwest corner of Alberta will be minimal. Those clear skies will contribute to rural areas – especially those along the foothills – experiencing cooler overnight temperatures and possibly some frost and/or fog in the early mornings. Cloud cover acts as an insulating layer, trapping heat escaping the surface overnight, and during seasons with few hours of sunlight the absence of cloud can really amplify the overnight cooling process. With lower overnight temperatures the natural evaporative processes can quickly saturate the air closer to the surface and create fog, especially in areas near water and/or with ample vegetation. Temperatures will start to moderate by the start of next weekend, and Calgary should return to daytime highs in the mid-teens again.
