Rounds of lake-effect snow into early next week
December 06, 2017; 4:55 PM
Highly amplified jet stream pattern currently in place across North America with a strong high pressure ridge anchored along the West Coast and a large trough over the East.
1. An extended spell of dry weather will remain across the interior West. I would be surprised if there was any measurable precipitation from south-central B.C. to southern Saskatchewan over the next 7 days.
2. The western ridge will also keep the cold air away from the West, though the nights will still get cold under clear skies and light winds, which will set up locally strong inversions through the mornings, which may trap fog and pollutants close to the ground. Afternoon temperatures will average 5-10 degrees Celcius. It will be above normal from Alberta to Saskatchewan for the next week.
3. Farther east, we will have several rounds of Arctic air spreading into the region from the northwest. As the cold air moves over the Great Lakes there will be locally heavy snowfall. Where that snow falls will greatly depend on the exact wind direction, which will be fluctuating from southwest to northwest over the next 5 days, making forecasts a challenge.
Through Thursday, it looks like the heaviest bands of snow will fluctuate between Orillia and Bracebridge in Ontario. There will also be some heavier snow in the Bruce Peninsula area.
By Friday, the bands will likely shift more north and fluctuate between Parry Sound and Huntsville in Ontario. There still may also be some heavier snow near Bracebridge.
Under these snow bands, the visibility may be close to zero with snowfall rates of 8-10 cm per hour, making travel extremely difficult.
Additional lake-effect snow will likely set up later in the weekend and into early next week. By early next week, we may have total snowfall amounts in excess of 75 cm in some areas.
4. In between the two lake-effect snow events we are expecting, an Alberta Clipper is set to track across the Lake Erie region Saturday and Saturday evening. This is the type of storm that does not have a lot of moisture, but it can cause a few hours of moderate to locally heavy snow with difficult driving conditions. Expect a general 2-8 cm of snow from southwestern Ontario to extreme southern Quebec from this feature. Behind this clipper, there will be a reinforcing shot of cold air.
5. The cold likely will hold tough in the East for the next week or so before trending back to normal. However, there are some signs of more cold coming into the central and parts of eastern Canada after Dec. 20.
6. It's still too early to speculate on whether we'll get a white Christmas or not.
The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com