The May long weekend forecast will be a bust with unsettled weather across the province. A potent low-pressure system in the eastern prairies will enhance the effects of a lee low expected to form in the foothills tonight. Cold air will be picked up from the low to the east and thrown into the system developing on the eastern slopes of the Rockies, causing precipitation to transition from rain to snow due to the colder temperature profiles. Yellow-level snowfall warnings have been issued along the foothills including Banff National Park with Environment and Climate Change Canada (ECCC) explaining, “Heavy snow with total amounts of 10 to 20 cm is expected this weekend. Locally higher amounts are possible. Scattered rain showers or flurries today will gradually transition to widespread heavy snow tonight. The snow will continue into Saturday.” Driving conditions around the Rockies are expected to deteriorate over the next 24 to 36 hours, with the weather agency advising, “Travel may be hazardous. Roads and walkways may be very difficult to navigate due to accumulating snow. Visibility may be reduced at times.” A special weather statement has been issued east and north of that snowfall warning – including for the City of Calgary. The statement is based on anticipated negative impacts to travel and the potential for that snow and/or mixed precipitation to extend beyond the snowfall warning. “Snow may affect areas as far east as Calgary Saturday morning. The heaviest snow will fall Saturday. Forecast snowfall amounts are highly uncertain. Accumulations of up to 20 centimetres are possible over higher terrain and along the Trans-Canada Highway west of Calgary,” ECCC said. Snow may briefly accumulate in areas east of the foothills where snowfall rates are high, or where surface temperatures are cooler. Yellow-level rainfall warnings have been issued for areas in northern Alberta due to that eastern system producing persistent rain on Friday. Total accumulations are expected to reach 25 to 50 millimetres, however some communities could record as much as 50 millimetres. “Near the Saskatchewan border, rain will transition to snow this morning. Closer to B.C., rain will continue until this evening,” the agency’s report reads. Beyond the obvious concern around that much rain, there is an additional consideration at play where that rain will go. ECCC says, “Due to recent and continued melt of the significantly above normal winter snowpack and recent overland flooding conditions, the ground likely has a reduced ability to absorb rainfall. Water will likely pool on roads and in low-lying areas.” On Friday afternoon and evening, there is also a risk of mild to moderate thunderstorms in Calgary and across southern Alberta. Daytime highs will be well-below seasonal for Saturday and Sunday with Calgary’s lows forecast to hover around 0 C. Lows outside of the city and/or in higher elevations could easily drop below freezing. The normal range in Calgary this time of year is 16 C for a daily high and 0 C for a daily low.
