It is important to note that this system brings a very tricky forecast because if models are off by even a fraction of a degree, it could significantly alter the mix of precipitation that an area sees. A subtle shift in the placement of the warm layer could either increase or decrease the overall impact dramatically.
As we have covered throughout the forecast, multiple areas of uncertainty remain, which should hopefully be cleared up by the time of our final forecast. Updated model data will help us refine the timing, precipitation types and amounts.
But with this being our preliminary forecast, we have initially gone with wider ranges on the forecast precipitation totals to cover the different scenarios. This is the most responsible approach when the atmosphere is finely balanced between different outcomes.
We expect to narrow these ranges in our final forecast as we gain better confidence in what will unfold. While significant changes to the overall setup are unlikely, we could see some shifts, with some areas jumping one category in either direction, especially if you are located right near the edge of one of the forecast zones.
Current indications suggest that the focus of the most significant impacts from this winter storm is likely to exist in a zone that encompasses Hamilton, Brantford, Burlington, Oakville, Cambridge, Guelph, Kitchener, Stratford, Woodstock, Mitchell, Listowel, Fergus, Arthur, Minto, Mildmay, Hanover, Chatsworth and Owen Sound. This is the area that currently has the highest risk for serious icing.
The predominant precipitation type throughout this event in that corridor is expected to be freezing rain, which may be quite heavy at times through the late morning and early afternoon. Periods of lighter freezing drizzle could fill in the gaps between heavier bursts.
This may reach ice storm levels, with the risk of widespread power outages through the hardest hit areas as the steady icing combined with strong wind gusts brings down tree branches and power lines. Travel may become dangerous or even impossible along some rural routes.
Ice accretion of 8 to 16 mm is possible here, and localized spots could see even higher amounts if heavier bands linger longer than expected. That much ice is more than enough to cause tree damage and infrastructure issues.
Another concerning aspect of this event is that much of this area is not expected to have a meaningful warm-up after the icing occurs. In fact, it is likely to remain below freezing through Thursday and into Friday.
That means impacts could persist for several days, as the ice will remain locked in place on surfaces, making cleanup and restoration efforts more challenging. Sidewalks, driveways and untreated back roads could remain treacherous well after the storm itself has moved on.
Further to the south and west, lower freezing rain accretion is expected as a transition to regular rain is expected for areas like the Niagara region through London and east of Lake Huron later in the morning. Here, temperatures rising above freezing will help limit ice buildup.
To the north and east of the main ice storm zone, we are expecting a zone including Dufferin County, along with Brampton, Vaughan, Mississauga and Toronto, to see a mix of all three wintry precipitation types. This is where the forecast becomes especially complex.
This will start with a few hours of freezing rain in the mid to late morning hours, amounting to up to 2 to 6 mm of ice accretion. Even on the lower end of that range, sidewalks and untreated surfaces will become slick.
By the late morning, this zone is expected to switch to ice pellets and then finally to heavy snow by the early afternoon. This changeover sequence will play a major role in how much snow is able to accumulate.
We have a large snowfall range here, with 5 cm on the low end and 15 cm on the upper end. This is due to the uncertainty around how long the ice pellets will last before switching over to snow.
If the switch over to snow happens faster than expected, this area could get closer to 15 cm of accumulation. A more delayed switch over would keep them closer to the 5 cm mark, as more of the precipitation would fall as denser, less-accumulating ice pellets.
Similarly, this uncertainty on the exact ratio of ice pellets and snow will be on display from the Bruce Peninsula through areas around Lake Simcoe and into Peterborough. Communities in this band will also see a wide spread of possible outcomes.
Snowfall totals here could range anywhere from 10 cm to 25 cm. Most models are showing a switch over to heavy snow by the late morning, which could allow many hours of steady heavy snow with hourly rates of 2 to 4 cm.
If this heavier snow scenario plays out, then general snowfall totals are likely to end up on the higher end of 15 to 25 cm. That would be enough to cause significant shovelling and plowing needs, along with difficult travel through the afternoon.
If more ice pellets mix in and continue for most of the event, it could keep totals as low as 10 cm, with more of the precipitation locked up as compact, crunchy pellets rather than fluffy snow. Even then, road conditions would still be quite poor.
Snowfall totals will drop off fast for regions further north into Central and Eastern Ontario. This is where the northern edge of the main snow band becomes more diffuse and less organized.
Disagreement in the models on how far north the band of snow will get means this corridor from Muskoka into Kingston could get anywhere from 2 cm to up to 10 cm of snow. Some towns could end up on the higher end if the band nudges a bit farther north than expected.
That drops down to 0 to 5 cm for Sudbury, through northern Muskoka, Bancroft and into Brockville. These areas will still see some impacts, but they should be less severe compared to the core zones further south, where ice and heavier snow are more likely.
