Xmas Winter Storm Eyes Southern Ontario With Up to 15–30cm of Snow and Ice Storm Risk; Heavy Rainfall in Eastern Ontario Washes Away Chance of a White Christmas
/THIS FORECAST HAS BEEN UPDATED
Here’s our latest forecast:
OLD FORECAST
This holiday season will likely be one to remember and not just with the ongoing pandemic that has changed how we celebrate, but a strong winter storm is set to bring a messy mix of precipitation across parts of Southern Ontario on Christmas. For many, this will be the perfect timing for a storm with limited travel (except for all the essential workers of course - thanks to them for keeping the province running!) occurring during Christmas this year. The effects of this winter storm will be vastly different depending on your location ranging from significant snowfall in Southwestern Ontario to heavy rainfall out in Eastern Ontario and the threat of prolonged freezing rain in between that.
We should note however that the current track of this system is still unclear with the models jumping between a more western track to an eastern track. This would change where the mixing line is located and who sees the freezing rain vs. heavy snowfall. With the map above, we have tried our best to go with the consensus between all the models. Some changes should be expected as we get closer especially in zone #2-4 where the gradient between the different precipitation types is extremely tight. The more eastern and western parts of the province have the highest confidence with either heavy snowfall or rainfall being the predominant precipitation type.
What we do know is that precipitation will begin to enter the province sometime early Thursday morning starting as rain. Temperatures will be quite warm as you wake up on Thursday ranging from 3 to 8°C but don’t let that fool you! As the system continues to spread across the region, we’ll see colder air start to flow into the province from the west during the afternoon hours causing the rain to transition over to heavy snow through Windsor and along the Lake Huron shoreline.
The cold air will likely make it as far as around Lake Simcoe before stalling out creating quiet the temperature gradient where for example, Windsor will be near -5°C or colder Christmas morning while Ottawa basks in double digits temperatures. With the cold air stalling out, it will create the perfect environment for several hours of freezing rain from the Northern GTA through Muskoka and in Algonquin Park. The heaviest freezing rain threat will exist from late Thursday evening into Christmas morning - power outages aren’t out of the question in areas that see the heavy freezing rain so plan accordingly. Again, this freezing rain zone may shift further west or east depending on where the cold air stalls out.
Total snowfall accumulation will be quite extensive for the western part of our regions with up to 15-30cm of snow possible for locations like London, Goderich, Owen Sound, Parry Sound, North Bay and Sudbury. Wouldn’t be surprised to see a few areas approach or even exceed the 30-40cm mark with lower amounts closer to 5-10cm for Windsor and Sarnia due to less moisture. To the east, the story will be heavy rainfall with totals between 20-40mm (locally up to 50mm especially around the Kingston area) throughout Eastern Ontario.
Between these zones, we’ll see a mix of rain, snow and freezing rain with more rain through more eastern parts of Central Ontario (Bancroft etc.) and into the GTA/Niagara region close to the lakeshore. The threat of freezing rain will get stronger away from Lake Ontario and further west from K/W, Guelph through York Region and up into Central Ontario (Barrie, Orillia, Bracebridge, Huntsville etc.). This is where between 5-15mm of ice accretion is possible. Snow will become the main story to the west of this region with a sharp cut off between who sees the heavy icing or heavy snowfall.
The impacts of this storm will continue throughout the day on Christmas with all areas transitioning over to snow by the afternoon. We could also see some strong snow squalls develop off Lake Huron and Georgian Bay as the system moves out of the region. At this point, the areas at the highest chance for the snow squalls include Muskoka, Parry Sound, Northern Simcoe County, Kincardine, Hanover, Owen Sound and Goderich. Snow squall activity will persist through the weekend with locally significant snowfall totals of over 25cm possible.
This storm will of course have a significant impact on the probability of waking up to a White Christmas in the morning across Southern Ontario. For much of Southern Ontario including Southwestern into Northeastern Ontario, a White Christmas is almost certain and we’ll even see the ‘perfect’ White Christmas where snow is coming down during the morning hours on Christmas. Unfortunately, the rain further east through Kingston and Ottawa will wash away any hope of a White Christmas.
There is some uncertainty through Central Ontario into the GTA where freezing rain could threaten a White Christmas but it should switch over to snow early in the morning especially the future west and away from the lakeshore you get. We’ve given the GTA lakeshore a 25% chance of a White Christmas with a 50% chance away from the lakeshore but this may change for the better or worse depending on the track of the storm. Our final White Christmas outlook will be issued Christmas Eve so we should have a better idea of the storm track.
