***NOTE: YOU CAN CLICK ON THE MAP TO OPEN A ZOOMABLE IMAGE***

Get your shovels ready, Southern Ontario! What many would consider our first true winter storm of the season is on the horizon. This moisture-laden system is set to arrive Wednesday afternoon, bringing heavy snowfall across a large portion of our region.

There’s still some uncertainty in the exact track, which will determine who sees the heaviest snow, but confidence is growing that much of Southern Ontario will experience significant impacts from this storm. Travel will likely become hazardous Wednesday evening into Thursday morning, and widespread school bus cancellations—and even full school closures—are almost certain on Thursday.

Based on the latest data, the heaviest snowfall is expected to stretch from Southwestern Ontario through Central Ontario and into the Ottawa Valley. Accumulations will likely range between 20 to 40 cm, with some localized pockets potentially exceeding 40 cm by the time the snow tapers off early Thursday afternoon.

The most challenging part of this forecast comes down to a narrow corridor from London through Hamilton, into the Greater Toronto Area (GTA), along the Lake Ontario shoreline, and into extreme Eastern Ontario along the international border. These areas are likely to start off with snow, but depending on the storm’s track, a transition to ice pellets, freezing rain, or even regular rain could occur during the evening and overnight.

The exact snowfall amounts in this corridor remain highly uncertain, as even a fraction of a degree difference in temperature could mean the difference between 5 cm and 30 cm of snow.

The risk of freezing rain also appears significant for areas in deep Southwestern Ontario, including Windsor, Chatham, and communities along the Lake Erie shoreline, where several hours of ice accretion could result in hazardous road conditions and localized power outages.

**PRECIPITATION TYPE** - MAP FROM WEATHERBELL

The storm will begin impacting Southern Ontario on Wednesday afternoon, with the initial bands of snow spreading into deep Southwestern Ontario, including Windsor, Sarnia, Chatham, and London. By the mid-to-late afternoon, snow will have moved into Hamilton, Niagara, and the Greater Toronto Area, just in time for the evening commute.

**HOURLY SNOWFALL RATE/intensity** - MAP FROM WEATHERBELL

Steady snowfall will continue through the dinner hour, with snowfall rates gradually increasing as the system spreads further across the region. Central and Eastern Ontario will see snow begin around the dinner hour into the early evening, while the Ottawa Valley may not see the first flakes until mid-to-late evening.

Snow will continue throughout the night across much of the region, with varying intensity. Unlike some past storms, this event isn’t expected to bring extreme snowfall rates, with accumulations of around 2 to 4 cm per hour at most. However, the prolonged nature of this storm, lasting 12 to 16 hours in many areas, will allow totals to build up significantly.

Another key factor in determining final snowfall amounts will be how far north the mixing line extends into Southern Ontario. Earlier model runs suggested a more northern track, which would allow warmer air to push into areas along the Lake Erie and Lake Ontario shorelines, leading to a transition from snow to ice pellets, freezing rain, or rain.

However, more recent model data from Monday evening has trended slightly further south, reducing the risk of mixing for some areas. That said, some models, including the American (NAM) and European models, still show a more northern mixing line, which could bring ice and rain into parts of deep Southwestern Ontario, London, and Hamilton.

If this occurs, Windsor and areas along the Lake Erie shoreline could see several hours of freezing rain, resulting in ice buildup on untreated surfaces, power lines, and roads.

On the other hand, the Canadian (RGEM) model, along with the higher-resolution American NAM 3km model, suggest a more southern storm track, which would keep most of Southern Ontario in the snow zone.

If this scenario plays out, snowfall accumulations could be much higher in places like London, Hamilton, and the Golden Horseshoe, with totals ranging from 20 to 30 cm and minimal mixing.

Some models also indicate the possibility of mixing slightly north of Lake Ontario and along the St. Lawrence River, including Kingston, Brockville, and Cornwall, which could lower snow totals in these areas. However, the latest data suggests this region may stay entirely on the snowy side of the system.

As the storm progresses overnight, those areas that remain on the snow side will continue to see accumulation through early Thursday morning. Snowfall rates could briefly reach 2 to 4 cm per hour in heavier bands but will likely average closer to 1 to 2 cm per hour.

Fortunately, winds won’t be particularly strong, with gusts expected to range from 20 to 40 km/h at most. While some blowing snow is possible, full-blown blizzard conditions are not expected with this storm.

By mid-morning Thursday, high-resolution models suggest a final burst of heavier snow around the Golden Horseshoe, Lake Simcoe, and Eastern Ontario. Snowfall rates could briefly spike to 4 to 6 cm per hour as the back end of the system moves through during the morning rush hour.

Travel conditions will likely be very poor on Thursday morning, and all non-essential travel should be avoided. Widespread school bus cancellations are almost a certainty given these conditions.

A rapid improvement is expected in Southwestern Ontario by late morning, with snowfall tapering off to light flurries. However, it will take time for road crews to clear the heavy snowfall, so road conditions may remain hazardous into the early afternoon.

For Central and Eastern Ontario, snow will linger into the early afternoon before finally winding down around midday for the GTA and Central Ontario and mid-afternoon for the Ottawa Valley.

By the time the storm wraps up, a broad region across Southern Ontario, including the Lake Huron shoreline, Sarnia, Kitchener, Barrie, Muskoka, Peterborough, and the Ottawa Valley, will likely see between 20 and 40 cm of fresh snow. Mixing is unlikely to be a factor in these areas, though there’s always a slight chance of a last-minute shift in the storm track.

The biggest uncertainty lies within a narrow corridor that includes London, Woodstock, Hamilton, Mississauga, Toronto, Belleville, Kingston, Brockville, and Cornwall. This area will likely begin with snow on Wednesday but could see ice pellets, freezing rain, or rain mix in during the late evening and overnight hours, which would reduce total snowfall amounts.

A conservative estimate for this region is at least 10 cm of snow, though some areas, particularly along the northern edge of this zone, could see totals closer to 20 to 30 cm. The current model trends lean toward a slightly more southern storm track, but we are waiting to see if this pattern holds before making final adjustments to the snowfall forecast.

For Windsor, Chatham, and areas along the Lake Erie shoreline, including Niagara, a mix of snow and freezing rain is expected. Some locations could experience several hours of freezing rain, leading to ice accretion of 4 to 8 mm, which may cause localized power outages. However, if the mixing line remains further south, these areas could still end up seeing significant snowfall, possibly exceeding 20 cm.

The bottom line is that while we have high confidence in a significant winter storm, the local impacts will ultimately depend on the storm’s exact track, which may not become fully clear until just before the system moves in.

A more detailed forecast with refined snowfall and freezing rain estimates will be released late Tuesday as newer model data becomes available.

Weather Forecasts & Articles

Major Winter Storm on Track to Dump Up to 40cm of Snow Across Most of Southern Ontario Starting Wednesday

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