First Messy Winter Storm of the Season Takes Aim at Southern Ontario Between Sunday & Monday; Damaging Wind Storm Overnight Sunday Possible

Forecast Discussion

We’re only a few days into December and already talking about the first winter storm of the season that could possibly affect Southern Ontario starting Sunday and lasting into Monday. Now, this system will be very location-dependent with some areas seeing mostly just rain, others seeing a mixed bag of wintery precipitation and heavy snow to the north. There will also be some quite strong winds associated with this system with gusts approaching 90-100km/h late Sunday evening and into Monday morning. The strongest wind gusts appear to be focused on Southwestern Ontario and through the GTA along with the shorelines of Lake Huron, Ontario and Erie. Wind damage along with power outages can’t be ruled out especially when combined with the freezing rain in some areas.

We will see the first bands of precipitation enter the region in the form of some wet snow during the afternoon on Sunday which will continue for areas north of Georgian Bay as more moisture is pumped into the region. Further south, another wave of precipitation will work its way across Southern Ontario from Michigan by the evening. At this point, temperatures through Southwestern Ontario and along the shoreline of Lake Huron, Erie and Ontario will be several degrees above the freezing mark so it should come down as rain with maybe some brief freezing rain in the higher elevations. This includes the GTA which should be mostly unaffected by this winter storm and will feel more like a damp and cold fall storm with rain and wind.

The concern with this system lies in the mixing zone further north from Central and Eastern Ontario with will be still a few degrees under the freezing mark going into the evening and overnight. There is some uncertainty around the extent of this cold air and how long it can hold up against the flow of warm air from the south. This will dictate the type of precipitation that comes down including freezing rain, ice pellets/sleet and snow. We are looking at a few hours of freezing rain extending from Owen Sound through the Dundalk Highlands and into the Ottawa Valley during the late evening and early overnight. This will transition over to regular rain overnight as temperatures rise above the freezing mark, but roads could still be quite icy.

Up into the southern part of the Bruce Penisula through Southern Muskoka and into Bancroft/Renfrew it will start as some ice pellets in the evening. Then a few hours of freezing rain overnight before transitioning over to regular rain by early morning. The more impactful wintery precipitation will be found north of a line stretching from Tobermory through Huntsville and into Pembroke where snowfall accumulation from 5-10cm during the evening and overnight is possible. This will switch over to ice pellets and maybe some brief freezing rain early Monday morning before some rain mixes in by sunrise. Northeastern Ontario including Sudbury and North Bay will come out on top when it comes to snowfall as they’re expected to remain on the cold side of this storm and pick up between 10-25cm by Monday morning.

All areas should rise above the freezing mark during the day on Monday which should help melt away any accumulation from the storm. However, the below-freezing temperatures return overnight into Tuesday so this may refreeze any precipitation still present on roads and make for icy conditions for Tuesday morning. And the lake effect snow machine may kick back into gear for Tuesday bringing the threat of more accumulating snow around Georgian Bay and Lake Huron.

More details on timing and accumulation will be released by Saturday evening in our full forecast. Keep in mind this forecast is preliminary and may be subjected to changes depending on the latest data. There is one model (the Canadian model) that shows a more southern scenario which would push the accumulating snow and freezing rain further south. However, we’re going with the consensus at the moment which is the more northern track.