Winter storm possible Thanksgiving weekend for MB/SK

Scroll to the end for breakdown of precipitation per region.

Monday October 12, 2020

Threat level: MODERATE

Impacts: LOW (based on population density)

Confidence: MODERATE (based on model agreements)

Expected hazards: WINTER STORM (possible) // STRONG WINDS // BLOWING SNOW

Expected snowfall: 10-30cm

Time frame: starting Sunday evening into Monday night

Locations impacted: Manitoba/Saskatchewan border

Expected watch: special weather statements, snowfall warnings and/or winter storm watches (localized)

Most likely areas impacted: areas of northeastern Saskatchewan and northwestern Manitoba along the provincial border.

Discussion: model consistency exists enough to give a Day 5 forecast and delineate a general risk area. Consistency with major trough ejecting across Prairie Provinces over the weekend bringing complex interaction between occluding front, warm front, cold front and trough (see below). A fast moving Alberta Clipper will move through the Prairies over the next 48hrs. Another surface low pressure develops in the lee of the Rockies this weekend, which will bring poleward advection of moist/warm air from the south and cold Arctic air into southern Saskatchewan/Manitoba on Sunday morning, bringing temperatures in the mid-teens to low 20's. Occluding front/cold front will move through the forecast area as low pressure begins its northeasterly track across N Manitoba. While it does so, it will drag Arctic air, aided by the trough, on the northwest-westerly side of the low pressure. The low appears to "spin in place" while occluding across northwestern Manitoba. This would bring a higher axis of precipitation in the forecast area, resembling more a Colorado Low, rather than an Alberta Clipper.

Low pressure system with trough (orange), occluded front (purple), warm front (red) and cold front (blue) with surface temperatures (in C) in the background by Sunday morning.

Temperatures will be cold enough on the backside of the low to bring measurable snowfall across the SK/MB border by Monday. With appreciable moisture and a seemingly fully saturated column, heavy snow will be possible in the ~15cm range, but could approach or surpass 30cm in localized areas where ground is relatively cold and higher elevation. Below are the last several GFS runs for precipitation type on Monday. As you can see, there are still some uncertainties ahead of this system.

Last 12 model runs (one ever 3hrs) of the GFS model

To make matters even more complicated, temperature will hover near the freezing mark. Therefore, there will be a very sharp transition zone somewhere near Flin Flon, MB. Anywhere west-northwest of this zone will receive heavy wet snow and anyone east-southeast of this zone will receive rain. Anyone sitting on this transition zone should experience freezing rain or sleet and then snow.

Therefore, we have made a breakdown of expected precipitation by area:

• Northeastern Saskatchewan: heavy snow

• Northern // Northwestern Manitoba: mixed-precipitation then snow

• Southern Saskatchewan: rain

• Southern Manitoba: rain

After this low has passed, southern Manitoba will likely experience lake-effect snow and flurries early next week as cold air flows across Lake Manitoba and Lake Winnipeg.