EARLY PREVIEW: Snowstorm Could Bring 15-25+cm of Snow to Eastern Parts of Southern Ontario on Monday

A very complex system is expected to track up the East Coast this weekend and has the potential to bring significant snowfall accumulation to parts of Southern Ontario starting Sunday night and continuing through Monday. This type of system is particularly a nightmare to forecast for Southern Ontario since the heaviest precipitation will track right along the American border with a very tight gradient between heavy snowfall and very little accumulation.

A slight change in the track of the system will have big impacts in terms of exactly how much snow will fall on our side of the border and how far west it will encompass. Considering we’re still over 48 hours away from the start of the snow, there’s a lot of time for the track to change as we get closer. However, there is some confidence in some parts of Southern Ontario and how they will be affected by this storm. This includes the Niagara Region and Eastern Ontario (Ottawa, Kingston, Brockville, Cornwall) which is very unlikely to escape this snowstorm unless it tracks significantly further east than expected.

Snow will start to pick up around the Niagara and Hamilton region sometime late Sunday evening or close to the midnight hour. It will continue to spread to the northeast throughout the overnight and into Monday morning. The worst conditions are expected during the early morning hours around Lake Ontario and later in the morning for Eastern Ontario.

Persistent snowfall will continue throughout the afternoon especially for Eastern Ontario, but it will begin to taper off starting from the southwest in the late afternoon and clearing in Eastern Ontario by midnight. Keep in mind this timing may change as we get closer since the system can slow down or speed up - we should have a better idea late Saturday on the exact timing.

There will also be wind gusts ranging from 40-70km/h accompanied by the heavy snowfall so driving conditions will likely be very poor with blowing snow possible. This snowstorm may impact the current plan for schools to return to in-person learning with school bus cancellations highly likely. The best chance at bus cancellations would be through the Niagara Region and Eastern Ontario with the probability decreasing the further to the northwest you go.

It’s a little too early to talk about exact snowfall accumulation due to the significant amount of uncertainty regarding the track of this system. We know that a lot of people do focus on the numbers so we have provided a very rough idea of the potential accumulation from this system. We have higher confidence in the Niagara Region and Eastern Ontario (the closer to the US border, the higher the probability) which could see snowfall accumulation of over 25cm by the end of Monday.

Those in Hamilton, Toronto, Peterborough and Bancroft are right on the line of seeing significant snowfall which makes this forecast very difficult. We’ve outlined the zone on the map (in the white hatched circle) we think could be subjected to very significant changes in the forecast depending on the track. Right now, we can say that there is a fair amount of confidence in accumulation over 10cm for those regions. However, we are being quite cautious with these numbers and some models are showing much higher totals than we’ve shown here. If the system maintains the current track, it wouldn’t be out of the question to see widespread accumulation between 20-40cm.

We believe it’s important to post a forecast this early due to the potentially significant impacts it could have on our region. This is now your chance to plan for a snowstorm and make any alternative arrangements for Monday should it occur. We can’t emphasize enough that this forecast will likely change. The best that can be done is to prepare for the worst and hope for the best, we don’t want you to be unprepared! There’s no harm in being over-prepared.

Check back on Saturday and Sunday for a more detailed forecast once we get more confidence in the track of the storm.