Canadian Prairie Snowstorm of Nov 7-9, 2020

 Meteorology 

A memorable, and perhaps record-breaking winter storm is set to impact much of the prairies this weekend, bringing heavy snow and strong winds that will likely make travel difficult to impossible at times through much of southern Saskatchewan and portions of southern Alberta.

As a large upper low/trough digs into the southwest US throughout the day on Saturday, a broad deformation zone develops from the northern US Rockies through southeastern Alberta northeastwards into the central prairies. Heavy snow will develop along this feature throughout the day on Saturday, with strong northerly winds developing by late day into southern Alberta, enhancing upslope effects in the southern foothills as well as along the north slope of the Cypress Hills, resulting in blowing and drifting snow throughout much of the southern half of the province. 

As a potent shortwave trough with increasing negative tilt begins to lift northeast out of the central and northern US Rockies, a strong area of low pressure departs the mountains of northern Wyoming and reconstitutes itself northeastwards along a barolinic zone through the Dakotas and into Manitoba by late Sunday evening. As isentropic lift increases throughout the day on Sunday poleward of the surface warm frontal zone, ice pellets and freezing rain are likely along an axis stretching from eastern Montana and extreme southeastern Saskatchewan, through southwestern and central Manitoba, and into far northwestern Ontario. Meanwhile, strong cold air advection northwest of the low begins to wrap increasingly cold air into the system, with heavy snow northwest of the low’s track developing from central Montana into southern Saskatchewan, and on into central and northern Manitoba, resulting in a second round of heavy accumulations across parts of the prairies. 

As strong surface pressure rises occur northwest of the low associated with cold air spilling southwards to the east of the Rockies, strong low level winds result from southeastern Alberta through southern Saskatchewan on Sunday – and, when combined with a 50+ knot northeasterly H850 jet resulting in strong wind gusts throughout southern Saskatchewan during the latter half of Sunday as the low reaches peak intensity – whiteout conditions will result in blowing and drifting snow, making travel difficult to impossible over a broad area. 

With a broad area of 30-50cm falling across the region, it is possible that several monthly 24 hour record snow totals could be broken across portions of Saskatchewan – especially where accumulations between both rounds of snow overlap. The snow moves out of the southern prairies on Monday morning, with cold temperatures and wind chills in its wake. 

Friday 18Z NAM prog valid 6PM CST Sunday, Nov 8. 
A potent "Wyoming" low cuts through the heart of the continent.

Impacts

It is highly likely that the greatest impacts will be to travel throughout the weekend, as road closures will become likely across parts of southern Alberta and much of southern Saskatchewan between late day Saturday and early Monday. Visibilities will be reduced to near zero in blizzard conditions, with winds having a strong crosswind component throughout the Trans-Canada Highway corridor west of Regina. Snow ploughs will likely have great difficulty keeping up with clearing off  ever-building snow drifts, as large amounts of snow will be available for transport in amply strong winds. As such, all travel should be avoided across the most heavily-impacted areas of the prairies this weekend. Those who must drive should exercise extreme caution and have an emergency safety kit in their vehicle that is easily accessible.

In addition, within the aforementioned corridor of freezing rain accumulations, ice accretion will likely yield slippery road conditions and perhaps some sporadic power outages in more heavily-affected areas. 

Friday 12Z ECMWF ensemble mean snow totals as of Monday at  6PM CST.