Environment Canada already has winter storm watches and a snowfall warning in place for parts of southwestern Alberta, therefore this discussion will focus on SK/MB. Below we will present the current model trends.
4:44 AM MDT Friday 27 September 2019 Winter storm watch in effect for areas in yellow:
A long duration snowfall event starting this evening through Monday is anticipated for parts of southwestern Alberta as a moisture laden Pacific weather system tracks through the area. There is still uncertainty around snowfall accumulations as warm surface temperatures will melt initial snowfall. There is also uncertainty as to how far east the snowfall with spread. Current indications suggest that by Monday, total accumulations of 15 to 30 cm over portions of southwestern Alberta are possible. For the extreme southwest corner of the province, upslope flow will enhance snowfall along higher terrain with localized snowfall totals of over 50 cm possible by Monday. Rapidly accumulating snow could make travel difficult over some locations. Travel is expected to be hazardous due to reduced visibility in some locations. Surfaces such as highways, roads, walkways and parking lots may become icy and slippery. Public Safety Canada encourages everyone to make an emergency plan and get an emergency kit with drinking water, food, medicine, a first-aid kit and a flashlight.
Let's dig right into it and see which way models are trending. I chose the GDPS (Canadian model) to be represented above, since it seems to relatively agree with the NAM 3km, NAM 12km and GFS over the last several runs. Therefore, we think the above precipitation-type scenario seems reasonable. Below we have outlined the potential impacts. Below is the model trend from the NAM depicting pockets of 20-30cm 12hr accumulations.
Saturday night - Tuesday
Threat level: MODERATE
Confidence: HIGH (based on model agreements)
Expected hazards: WINTER STORM // HEAVY SNOWFALL // STRONG WINDS
Expected snowfall: ~20cm southern SK // +20cm extreme SW SK (possibly less due to warm soils) // 10-15cm Riding Mountain Prov Park (possibly less due to warm soils)
Locations impacted: Most of southern Saskatchewan // Riding Mountain Prov Park
Timing: Saturday night through Tuesday evening-night
Expected watch: special weather statements, snowfall warnings and/or winter storm watches
Discussion: please note that our forecast above has omitted Alberta, since ECCC already has watches/warnings and discussions out for Alberta. This forecast is focused towards Saskatchewan. Manitoba should be near the transition zone and is expected to get mostly rain out of this, except for areas of higher terrain, which could see snow, but accumulation is uncertain due to warm soils and possible wet surface (due to rain). Accumulation above a few centimetres is not likely in Manitoba at this time.