Multi-Day Winter Storm to Affect Southern Ontario Starting Monday With Heavy Snow and Rain; Blizzard Conditions Possible in Some Areas on Tuesday

As we’ve been covering over the past few days, a prolonged winter storm is expected to move into Southern Ontario during the final days of November. This storm is quite a nightmare to forecast as we have so many variables to deal with including temperatures, precipitation type, intensity and lake enhancement just to mention a few. That means we have a lot of information and maps contained in this forecast which will hopefully help you plan your activities in the coming days.

TIMING

We’ll start with Monday morning as the system begins to enter the province starting with Southwestern Ontario during the mid-morning hours and spreading across the rest of the region throughout the late morning. For almost everyone, it will start as rain for at least the first few hours with temperatures several degrees above the freezing mark. Colder air will slowly move in from the west starting first with the Windsor/Sarnia area around 8-9 AM as the rain transitions over to snow towards the later morning hours. This transition will occur next for the Goderich and Grey-Bruce region around the noon hour beginning with the Bruce Peninsula and spreading along the Lake Huron shoreline.

As we head into the afternoon, more areas away from the Lake Ontario shoreline will begin to mix in some wet snow with a few hours of heavy snow later in the afternoon. This includes much of Central and Southwestern Ontario especially around the southern Georgian Bay shoreline due to some lake enhancement. For the GTA and Niagara region, the rain will continue into the dinner hour before it begins to switch over to snow as the colder air builds in just in time for the evening rush hour. Expect some messy road conditions for the evening so be sure to travel with caution. Rainfall will begin during the late morning hours for Eastern Ontario and continue throughout the day heavy at times. Some snow will mix in through the higher elevations later in the afternoon including Bancroft and Pembroke but most of Eastern Ontario should stay all rain into Tuesday.

ACCUMULATION

For this event, we’ve decided it is best to break the snowfall down by each day. Although it should be mentioned that total accumulation over the 3 days could exceed 30-50cm especially around the Southern shoreline of Georgian Bay. The heaviest snowfall accumulation by the end of the day on Monday is expected to be found in the higher elevations near the Quebec border including Algonquin Park, Bancroft and Barry’s Bay along with a small zone just south of Georgian Bay that includes Wiarton, Meaford and Collingwood. These areas could see as much as 12-20cm by midnight (however snow won’t end at midnight and the additional accumulation will be included in Tuesday’s forecast) with locally as much as 25cm. Outside of this area, the forecast becomes very tricky because it’s very temperature-dependent and models are still disagreeing on the exact accumulation.

Our forecast assumes no melting occurs which is pretty unrealistic given that temperatures will still be above the freezing mark when the switch over occurs so consider this the max possible accumulation - some areas will likely get much less than forecast. With that being said, the rest of Southwestern Ontario into parts of Central Ontario including Windsor, London, K/W, Barrie and Muskoka have the potential to see between 6-12cm of accumulation. Less than 6cm is expected directly east of Georgian Bay and through the Northern GTA away from the lakeshore. Downtown Toronto and the Niagra region will likely see little to no accumulation by the end of Monday only switching over the wet snow during the evening.

For those that don’t see the snowfall accumulation, you won’t exactly be spared with this system but it will come down as heavy rainfall instead. Rainfall totals for Eastern Ontario into the GTA/Niagara region will range from 20-30mm by Tuesday (we didn’t break this down by day because most of the rain will come on Monday). This is actually a fair amount of rain for this time of the year so there could be some localized flooding in low-lying areas especially since the rain will come down heavy at times. The rest of Southern Ontario can expect between 10-20mm of rainfall before switching over to snow with less than 10mm through Windsor, regions east of Lake Huron and into the higher elevations Central Ontario where less rain is expected before the switch over occurs.

As we move into Tuesday you might be thinking that this storm was more bark than bite but remember this isn’t a typical storm that is contained to a 12-24 timeframe - this will be a multi-day event. That will quickly become apparent as you wake up Tuesday morning and throughout the day as the story shifts from the messy mix that we saw on Monday towards heavy lake enhanced snow and blizzard conditions in some areas with strong gusty winds. As the low-pressure system begins to stall out over the region it will seem like a never-ending flow of moisture as bands of snow circulate the stalled-out system.

In general, the bands won’t be very strong with some light snow for most areas but the problem is that colder air will allow the lakes mainly Georgian Bay and Lake Huron to increase the snowfall rates for some surrounding regions. Current data suggests those regions will include the Bruce Peninsula through the southern shoreline of Georgian Bay like Meaford and Collingwood and another zone southeast of Lake Huron just to the west of London. These areas may see between 20-30cm of snowfall accumulation by the end of Tuesday will locally higher amounts. Strong wind gusts between 40-70km/h will also present a big issue combined with the heavy snowfall early Tuesday which may result in some blowing snow and localized blizzard-like conditions around Lake Huron and Georgian Bay. Wind gusts will subside later in the day on Tuesday.

The remaining regions around Lake Huron and Georgian Bay can expect as much as 12-20cm with lesser amounts further inland with around 6-12cm for the rest of Southwestern and Central Ontario. Near the Lake Ontario shoreline, there will still be some rain continuing early Tuesday morning so total snowfall accumulation will be lower around 2-6cm. Little to no accumulation is expected for Eastern Ontario. It’s important to mention that this isn’t a final forecast for Tuesday as we’re dealing with lake-related snowfall which is very tricky to pin down. If needed, we’ll have an updated snowfall map for Tuesday posted sometime Monday. Snowfall will also continue into Wednesday which we’ll have a separate forecast for that as we get closer and more certain on what will happen.