Colder air to bring lake-effect snow to parts of Manitoba

Story by Lance Quackenbush

Edited by Francis Lavigne-Theriault

Friday October 16, 2020

Threat level: MODERATE

Impacts: LOW (based on population density)

Confidence: HIGH (based on model agreements)

Expected hazards: SNOW SQUALLS

Expected snowfall: 10-20cm, with locally higher snowfalls

Time frame: starting Thursday morning, intensifying into the evening and overnight, and tapering to flurries by Friday afternoon

Locations impacted: Poplar National Park Region in Manitoba

Expected watch: special weather statements

Most likely areas impacted: Areas east of Lake Winnipeg

SNowfall accumulation by Friday October 16, 2020

Discussion: Regional and global models are showing a substantial risk of major lake-effect snows off Lake Winnipeg beginning Thursday morning. A trough is forecast to move over Manitoba Thursday night in association with a stationary low near the border with Nunavut as a second area of low pressure slides east over Hudson Bay. The interaction will bring down a much colder Arctic air mass, which will cause a change in wind direction to the northwest at the surface. This flow, combined with warm waters over Lake Winnipeg, will set up bands of lake effect snow east of the lake. The winds should become light and shift on Friday in the afternoon, allowing the snow to taper off to flurries.

Overnight Thursday surface map showing a trough (orange) moving across Manitoba into northwestern Ontario

850mb temperatures will fall to -10 to -13°C range across the region by Friday morning behind the trough. A 40km/h northwest wind at the 850mb level and 20km/h surface wind will pick up moisture from the warm Lake Winnipeg, which still has water temperatures around 8-9°C across northern sections and 10-11°C across the south. The temperature differences between the water and the air at 850mb, combined with the northwest wind, will create lake-effect snow bands. Surface temperatures will also be below freezing Thursday night across the province, allowing for snows to accumulate on any snow squall that develops.

RDPS Model derived 7am Temperatures for Manitoba on Friday Morning

The area most likely to see heavy snow will be the Poplar Park region and areas south of it as they will be downwind in the prevailing wind direction. 10-20cm will be on the table, with locally higher amounts in the most intense bands. A few flurries or periods of light snow will also be possible for Winnipeg itself with lighter snows of 2-4cm possible off of Lake Winnipegosis. Another round of lake-effect snow could occur on the weekend as another trough will move through Manitoba, however the winds look to be more northerly, which may bring less impacts than Friday’s potential. However, the weekend will have to be monitored for the risk of more snow.