A Nightmare Before Christmas as Snowstorm Targets Southern Ontario on Monday With Up to 10-20cm of Snow

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Are you dreaming of a White Christmas? Well, it looks like luck is on your side as a snowy system is poised to sweep across Southern Ontario just days before Christmas. However, this snowfall won’t come without consequences, as it is expected to bring a significant amount of snow to some areas and could disrupt holiday travel plans right before Christmas.

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Snow is anticipated to start early Monday and persist throughout the day, bringing moderate to heavy snowfall across a wide area of the region. Central and Eastern Ontario are likely to bear the brunt of this storm, with total snowfall amounts ranging from 10 to 20cm expected by early Tuesday morning.

In contrast, Deep Southwestern Ontario and areas along the Lake Ontario shoreline, including the Greater Toronto Area GTA, are expected to experience lesser impacts from this system. This is primarily due to the majority of the precipitation staying further north, and any moisture reaching the south being met with slightly warmer air, resulting in wetter snow and reduced accumulation.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

According to the latest data, initial bands of snow are projected to move into the Bruce Peninsula and Georgian Bay areas by mid to late morning on Monday. The snow will then spread eastward, encompassing Eastern Ontario and all regions by early afternoon.

The heaviest snowfall is likely to be concentrated east of Georgian Bay, possibly enhanced by minor lake effects. By late afternoon, snowfall will also begin in Southwestern Ontario, with a chance of some mixing, including ice pellets and wet snow, particularly in Deep Southwestern Ontario around Windsor.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

The most challenging conditions are expected during the afternoon and evening hours, as steady snow covers much of Southern Ontario. Occasional moderate wind gusts up to 40 km/h may lead to blowing snow and reduced visibility. If travel is necessary during this time, exercise extreme caution, and consider postponing travel until Tuesday when conditions are expected to improve significantly.

Temperatures are forecasted to gradually warm up during the evening, approaching the freezing mark around Lake Ontario and Lake Erie. This may cause existing snow to transition to a mix of wet snow and rain, potentially resulting in lower snowfall totals in these areas.

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Light snow will continue past midnight into early Tuesday morning but will diminish in intensity as the night progresses. Western regions should see snow taper off shortly after midnight, while Eastern Ontario may experience lingering snow until late morning.

Overnight, there is concern about rain mixing in along the Golden Horseshoe as temperatures rise further, potentially melting any earlier snow and jeopardizing the chances of a White Christmas in those areas. We will closely monitor this development as it unfolds.

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Snowfall accumulation is expected to range from 10-20cm across Central and Eastern Ontario, including areas like Grey-Bruce, Barrie, Orillia, Huntsville, North Bay, and the Ottawa Valley. Some localized spots, particularly east of Georgian Bay and into the Ottawa Valley, could see up to 25cm of snow.

Further south and west, 5-10cm of snow is anticipated east of Lake Huron, extending into the Golden Horseshoe away from the shoreline, including cities like London, Woodstock, Kitchener, Guelph, Mississauga, and Orangeville.

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Toronto, Oakville, Burlington, Hamilton, the Niagara region, and Deep Southwestern Ontario, such as Chatham, Sarnia, and Windsor, are expected to receive less than 5cm of snow. Windsor may see minimal snow if the transition to rain occurs earlier than anticipated. There remains a possibility for the GTA to exceed forecasted amounts if cold air persists and prevents mixing.

It’s a Christmas Miracle! A White Christmas Is Likely for Most of Ontario & Quebec This Year

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The month of December has truly delivered a winter wonderland for much of Ontario and Quebec, especially in the snowbelt regions of Ontario, which have seen significant snowfall from several rounds of snow squalls in recent weeks.

With Christmas just around the corner—less than five days away—the question on everyone’s mind is whether we’ll wake up to a White Christmas or a Green Christmas this year.

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For clarity, Environment Canada defines a "White Christmas" as having at least 2 cm of snow on the ground at 7 a.m. Christmas morning. Unfortunately, in recent years, Southern Ontario’s holiday season has often been marked by the Grinch’s meddling, with last year seeing widespread "Grinchmas" conditions.

Currently, the snowpack across much of the region is quite substantial, particularly east of Georgian Bay, into Northern Ontario, and across Quebec. The good news for these areas is that the forecast suggests little to no rain or mild temperatures between now and Christmas, making a White Christmas virtually guaranteed.

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However, the story is quite different for southern portions of the region, including Deep Southwestern Ontario and the Golden Horseshoe. These areas haven’t seen much in the way of significant snowfall accumulation this month, and the forecast includes a stretch of above-freezing temperatures on Christmas Eve and Christmas Day.

As a result, the odds of a White Christmas here depend entirely on whether snow can accumulate between now and Christmas morning.

Thankfully, hope isn’t entirely lost! A developing system is expected to move into Southern Ontario early Monday, continuing into Christmas Eve on Tuesday. Recent model updates have been promising for snow lovers, trending toward a stronger system that brings more widespread snowfall.

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Current projections suggest this system could deliver 10–20 cm of snow across Central and Eastern Ontario. However, for those along the Lake Ontario and Lake Erie shorelines, including parts of the GTA and Niagara Region, snowfall amounts may be significantly lower due to temperatures rising above freezing during the day on Monday. This could lead to melting or even a mix with rain, reducing accumulation to just a few centimeters.

With temperatures hovering slightly above freezing through Christmas Eve, it’s uncertain whether any snow from this system will survive until Christmas morning in these areas.

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WHITE CHRISTMAS REGIONAL BREAKDOWN

Central Ontario, including Muskoka, Tobermory, Bancroft, and Algonquin Park, has the best odds in Southern Ontario. These areas already boast a healthy snowpack from earlier systems and lake-effect snow, and Monday’s storm will only add to it. Temperatures are expected to remain below freezing, ensuring the snow sticks around. The chance of a White Christmas here is over 90%.

Eastern Ontario and areas near Lake Huron, including the Ottawa Valley and regions around Lake Simcoe, have a slightly lower chance at 75%. Eastern Ontario currently has little snow on the ground, but Monday’s system is expected to change that. Lake Huron’s shoreline, while already snow-covered, will face a brief warm-up Monday into Christmas Eve. While the snow is likely to hold, it isn’t guaranteed.

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For areas like Sarnia, London, Kitchener, Guelph, and Belleville, the chance of a White Christmas is more uncertain at 50%. Everything depends on how much snow Monday’s system delivers and whether it can survive the milder temperatures leading into Christmas morning.

In the GTA, including Hamilton and northern parts of Niagara, the odds of a White Christmas are slim with a 25% chance. Without an existing snowpack and with limited accumulation expected from Monday’s storm, above-freezing temperatures are likely to melt any snow that does fall. However, if the storm overperforms or the warm-up is less intense, we could see a last-minute boost in probabilities.

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Deep Southwestern Ontario, including Windsor and areas along the Lake Erie shoreline, is the least likely to see a White Christmas, with just a 10% chance. Monday’s system is forecast to bring minimal snow, and the prolonged warm-up will likely ensure a Green Christmas here.

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Northern Ontario offers little drama in this forecast. With widespread snow on the ground and no significant warm-up in sight, the region enjoys a 90%+ chance of a White Christmas across the board.

Much of Quebec also looks set for a picturesque holiday. The exception is the Montreal area, which currently has limited snow on the ground. However, like Eastern Ontario, this should change once Monday’s system moves through.

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This forecast remains preliminary and will be updated as we approach Christmas. Our final White Christmas forecast, set to be released on Christmas Eve, will factor in Monday’s storm and provide a clearer picture. If the snow cooperates, expect to see more 90%+ zones on the map. Stay tuned, and let’s hope for a festive, snow-covered holiday!

Pre-Christmas Squalls Could Bring Up to 25-50cm of Snow on Saturday to Parts of Southwestern Ontario

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As we approach the final weekend before Christmas, Southern Ontario is gearing up for the coldest air of the season so far. With the lakes still unfrozen after the unseasonably mild fall, conditions are setting up perfectly for the lake effect snow machine to roar back to life, particularly off Lake Huron.

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Lake effect snow squalls are expected to develop as early as Friday evening along the southern shoreline of Lake Huron and persist through much of Saturday. Current indications suggest the heaviest snowfall will target the corridor between Sarnia and Strathroy. By the time the squalls taper off late Saturday, some areas could be buried under 25 to 50 cm of fresh snow.

This snowfall is promising news for those hoping for a White Christmas. With below-freezing temperatures expected to last through Tuesday, the snow should be deep enough to hold on despite a brief warm-up on Christmas Eve into Christmas Day when temperatures may climb above freezing.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

Based on the latest data, a fairly intense snow squall is anticipated to form around midnight, likely affecting areas between Petrolia and Strathroy. However, the exact location of this band remains uncertain and will determine which areas see the most significant snow. The best bet at this time places the heaviest snow over Port Franks, Lambton Shores, and Kettle Point.

The squall is expected to persist through the overnight hours into early Saturday morning, bringing dangerous travel conditions in the affected regions. Rapidly accumulating snow combined with near-zero visibility will likely lead to road and highway closures. There’s also potential for the squall to extend further inland, possibly reaching areas northeast of Chatham along the Lake Erie shoreline.

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Meanwhile, locations along the eastern shoreline of Lake Huron, from Kincardine to Grand Bend, may experience occasional bursts of heavy snow as the squall shifts and clips the shoreline.

By late Saturday morning and into the afternoon, the lake effect activity south of Lake Huron is expected to weaken as the band becomes more spread out and less organized. The squall should gradually diminish and retreat closer to the shoreline by Saturday evening, eventually fizzling out overnight into early Sunday morning.

In addition to the Lake Huron squalls, minor lake effect activity is possible south of Georgian Bay, including areas like Owen Sound, Meaford, and Collingwood. However, this activity is not expected to be as intense, with light to moderate snowfall likely throughout the day on Saturday.

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When it comes to snowfall accumulation, variability is the nature of lake effect events. Narrow squalls can lock into a region and dump significant snow over a small area while sparing nearby locations.

We currently expect areas including Warwick, Watford, Forest, and Lambton Shores to receive between 25 to 50 cm of snow by the end of Saturday, with localized totals possibly exceeding 50 cm in some spots, although this is likely an overestimate.

The gradient will be sharp, with Petrolia and Grand Bend potentially seeing 15 to 25 cm. Sarnia and Strathroy, on the outskirts of the main activity, are likely to receive just 2 to 5 cm, although even a slight shift in the squall’s position could put these areas into the heavier snow zone.

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Further up the eastern Lake Huron shoreline, locations from Kincardine to Grand Bend could see 5 to 15 cm of snow, with most areas leaning toward the lower end of that range.

South of Georgian Bay, including Owen Sound, Meaford, and Collingwood, snowfall is expected to range between 2 to 5 cm, with localized amounts up to 10 cm possible if the activity becomes more organized.

Elsewhere, the Niagara Region could pick up 2 to 5 cm of snow overnight into early Saturday morning as lingering precipitation from a previous system continues.

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For the rest of Southern Ontario, no significant snowfall is expected this weekend. However, we are closely monitoring a potential snowmaker early next week between Monday and Tuesday, which has been trending stronger in recent model data. This system could bring heavy snow to parts of Southern Ontario, maybe sealing the deal on a White Christmas for many. We’ll provide more details on that in a separate forecast.

'Snow Day' Forecast: Slight Chance of School Bus Cancellations in the GTA on Friday

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A system is forecast to arrive in Southwestern Ontario late Thursday, bringing light to moderate snowfall to the region overnight and into Friday morning. Along with this system, a lake-effect snow band is expected to form early Friday morning, affecting parts of the Greater Toronto Area (GTA) west of Lake Ontario.

While the overall snowfall accumulation will not be particularly significant—most areas will see 2-5 cm, with localized amounts of up to 15 cm in the lake-effect snow zone—the potential for reduced visibility is a concern. This will be especially true for the stretch between Toronto and Burlington during the Friday morning rush hour. As a result, there is a possibility of school bus cancellations, though it remains uncertain.

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The highest likelihood of cancellations is in the southern parts of Peel and Halton regions, where the most intense snow squall activity is expected. However, the probability is estimated at only 50%, as urban school boards in these areas typically require more substantial impacts to cancel buses. The decision will hinge on the strength of the snow band and whether it causes significant road issues when cancellation decisions are made in the early morning.

In surrounding areas, including Toronto and northern Halton, there is a slight chance (about 25%) of cancellations. While unlikely, the possibility cannot be entirely ruled out if conditions worsen unexpectedly.

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Elsewhere in Southwestern Ontario, the probability of cancellations is very low to low. The system's expected snowfall alone is insufficient to prompt widespread cancellations. However, some localized areas may experience reduced visibility during the morning commute, which could lead to isolated decisions by individual school boards to cancel buses as a precaution.

For Central and Eastern Ontario, no school bus cancellations are anticipated, as these regions are not expected to see significant snowfall from this system.

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As Friday marks the last school day before the holiday break, this will be our final snow day forecast for 2024. Thank you for relying on us for your snow day probability updates throughout the year. Our forecasts will resume the week of January 6th. Have a safe and happy holiday season!

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

Snow Squall May Disrupt Friday Morning Commute in the GTA; Locally 10-20cm of Snow Possible

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Southern Ontario has enjoyed a relatively calm week of weather, offering a welcome break for those still recovering from the heavy snow squalls that hammered parts of the snowbelt earlier this month. However, as the saying goes, all good things must come to an end, and this tranquil pattern is set to change as we approach the end of the week.

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For a twist, the snowbelt won’t be the epicenter of the heaviest snowfall this time. Instead, the Greater Toronto Area (GTA), which has largely avoided winter’s worst so far, will be in the spotlight.

A weak system is forecast to sweep across Southern Ontario late Thursday into Friday, but the real story lies in a rare phenomenon: lake-enhanced snowfall and localized snow squalls along the western shoreline of Lake Ontario. These conditions could deliver a sudden 10-15 cm of snow, with localized totals nearing 20 cm in parts of the western GTA between Thursday night and early Friday morning.

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Most other areas in Southern Ontario will see much less snow, with accumulations generally staying under 5 cm. As you move into Central and Eastern Ontario, snowfall will likely be limited to trace amounts. After the snow, attention will shift to an impending blast of Arctic air this weekend, bringing wind chills as cold as -30°C on Sunday and Monday.

The snowfall is expected to begin in Deep Southwestern Ontario on Thursday evening, with light to moderate bands moving eastward. While initial impacts will likely be minimal, drivers should still exercise caution as roads may become slushy with reduced visibility. By midnight, the snow will have reached the Golden Horseshoe, blanketing the region with light to moderate snowfall through the early hours of Friday.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

A key feature of this system will be a concentrated band of heavy snow forming off Lake Ontario, likely impacting areas between Toronto and Burlington early Friday morning. This narrow band could initially affect Toronto and Mississauga before shifting southward into Oakville, Burlington, and eventually Hamilton. If this snow squall becomes stationary for an extended period, it could deliver intense snowfall rates of 2-4 cm per hour, rapidly accumulating 10-15 cm or more in a short time.

This timing is particularly concerning as the squall is expected to peak during Friday’s morning rush hour. Commuters in the western GTA should prepare for challenging conditions, including near-zero visibility and rapidly deteriorating roads. By early Friday afternoon, the lake effect activity should taper off as the system exits the province, though some lingering lake effect flurries may persist near Lake Ontario and along Georgian Bay's southern shoreline into Friday evening.

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Given the highly localized nature of snow squalls, snowfall totals will vary significantly over short distances. Areas between Toronto and Burlington are most likely to see accumulations of 10-15 cm, with a slim chance of localized amounts reaching 20-25 cm if conditions align perfectly. That said, such higher totals are likely overestimations, though similar events in the past have exceeded expectations.

Beyond the GTA, snowfall amounts of 5-10 cm are expected in Hamilton, parts of the Niagara Region, and areas like the Dundalk Highlands and Georgian Bay’s southern shoreline, where some enhancement to the system is likely.

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Elsewhere in Southwestern Ontario and regions around Lake Simcoe, 2-5 cm is expected, although there is some uncertainty about the system's moisture content, which could lead to slightly higher totals. Windsor, Central Ontario, and Eastern Ontario are expected to receive trace amounts of snow.

Looking ahead to the weekend, a surge of Arctic air will settle over Southern Ontario starting Saturday, with Sunday morning lows dipping well below -20°C across much of the region. In addition to the bitter cold, lake-effect snow is expected to return south of Lake Huron as early as Friday evening, potentially impacting areas like Sarnia, Petrolia, Port Franks, and Grand Bend.

These regions could see localized snowfall totals of 15-30 cm by Saturday. More details on this development will be provided in an upcoming forecast.

'Snow Day' Forecast: Extra Long Weekend for Some Students in Ontario as Squall Likely to Cancel Buses on Friday

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Intense snow squall activity is forecasted to bring a significant amount of snow to parts of the snowbelt region east of Lake Huron and Georgian Bay overnight and into Friday morning.

These squalls are expected to persist through the morning hours, creating hazardous conditions with near-zero visibility on the roads. Given these dangerous travel conditions, it is highly likely that many school boards will opt to cancel buses for Friday. For some areas, this would mark the second snow day in a row, as buses were already canceled on Thursday.

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The highest confidence for school bus cancellations remains in areas like Grey-Bruce, Avon Maitland (Goderich), Simcoe (North), Trillium (Muskoka), and Near North (Parry Sound). With active snow squall warnings in place and the potential for over 50 cm of snow to accumulate overnight, there’s little doubt that buses will be unable to operate safely in these regions. We’re assigning a 90% probability of cancellations in these zones.

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Outside the core snowbelt areas, the situation becomes less certain. For locations such as Listowel, Simcoe (West), and Trillium (Haliburton), we estimate a 75% chance of cancellations. While they are fairly likely, it’s not a guarantee. Regions including the rest of the Avon Maitland District School Board (AMDSB), Wellington, Dufferin, Simcoe (Central), Trillium (Kawartha), and East Parry Sound have a 50% chance of seeing cancellations, as snowfall in these areas is expected to be less intense or more variable.

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For the rest of Southern Ontario, school bus cancellations on Friday are unlikely since the snow squall activity will remain localized to the snowbelt. This means a sharp drop-off in probabilities as you move farther away from the areas most heavily affected.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

'Snow Day' Forecast: Blizzard Conditions on Thursday Likely to Cancel Many School Buses in Southern Ontario’s Snowbelt

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Snow squalls are forecast to develop late Wednesday and persist into Thursday, bringing substantial snowfall to areas around Lake Huron and Georgian Bay.

Strong wind gusts are expected to accompany the intense snowfall, prompting Environment Canada to issue a rare blizzard warning for parts of Grey, Bruce, and Huron counties. Meanwhile, other regions are under a strongly worded snow squall warning, with predictions of snowfall accumulation potentially reaching up to 80 cm in localized areas.

Given the expected hazardous conditions, it’s highly unlikely that school buses will be able to operate safely in the affected areas on Thursday. As a result, it is anticipated that many school boards will opt to cancel school buses and might even decide to close schools entirely, particularly in regions under a blizzard warning.

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The highest likelihood of a ‘snow day’ applies to the entire Bluewater District School Board (BWDSB), Avon Maitland District School Board (AMDSB) - North Huron, Simcoe County District School Board (North and West weather zones), Trillium Lakelands District School Board (Muskoka region), and Near North District School Board (NNDSB - Parry Sound area).

These areas, which are under snow squall or blizzard warnings, have a greater than 90% chance of bus cancellations.

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Surrounding regions, including the remainder of Avon Maitland District School Board (southern zones), Simcoe County District School Board (Central and South weather zones), Student Transportation Services of Wellington Dufferin (STWDSTS), and Trillium Lakelands District School Board (Kawartha Lakes and Haliburton regions), have a 50–75% chance of snow day cancellations.

Although these areas are still under warnings, they are not expected to experience the most severe conditions. While bus cancellations are still likely, the confidence level isn’t as high as in the core impact zones.

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The probability of cancellations drops significantly outside the snowbelt, as the squalls are expected to remain highly localized. Eastern Ontario may be the only exception outside the snowbelt which has a low chance (10–25%) of cancellations.

While icy road conditions from an overnight freeze following earlier rainfall are possible, it is unlikely to be severe enough to prompt widespread cancellations. However, the possibility cannot be entirely ruled out.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

Return of Squalls to Ontario’s Snowbelt This Week With Blizzard Conditions & Over 50cm of Snow Possible

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While the brief break from lake-effect snow earlier this month brought milder air and rain to the snowbelt regions, the respite appears to be short-lived.

Snow squall activity is expected to make a comeback as we approach the end of the week. With multiple days of snow squalls anticipated, we could once again see impressive snowfall totals, rivaling those from earlier this month.

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Colder air will begin to filter into Southern Ontario from the northwest late Wednesday afternoon, dropping temperatures below freezing through the evening. This influx of cold air will trigger the development of lake-effect snow bands, with ideal conditions persisting through Thursday and into Friday.

Current projections suggest two primary zones will bear the brunt of the snow squalls: one east of Lake Huron and the other southeast of Georgian Bay. The Lake Huron squall is expected to impact southern portions of Grey and Bruce counties, including Owen Sound, Chatsworth, and Meaford. Meanwhile, the Georgian Bay squall will likely target central Simcoe County, extending northward into southern Muskoka.

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Snowfall totals in the hardest-hit areas could exceed 50 cm, with the possibility of approaching the staggering 100 cm seen in Bracebridge and Gravenhurst earlier this month. Whether such totals materialize depends on whether any of the snow squall bands remain stationary for extended periods.

To make matters worse, strong winds are expected to develop late Wednesday and persist into Thursday morning. Gusts could reach 60–80 km/h, particularly in Grey-Bruce and Simcoe County, significantly reducing visibility and creating hazardous travel conditions.

Blizzard conditions may develop, and travel is strongly discouraged during this timeframe. School bus cancellations are almost certain along the Lake Huron and Georgian Bay shorelines on Thursday.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

The lake-effect snow is expected to begin late Wednesday afternoon, with the first band forming off Lake Huron. Initially driven by northwesterly winds, this band will target areas near Goderich before shifting northward as winds veer to a more westerly direction by evening.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

By midnight, the main Lake Huron squall is expected to become stationary, affecting areas from Wiarton southward to Port Elgin, Owen Sound, and Meaford. Simultaneously, snow bands will begin forming off Georgian Bay, initially targeting Wasaga Beach, Midland, and Orillia. These may briefly lift northward Thursday morning, potentially reaching Gravenhurst and Bracebridge.

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HOURLY SNOWFALL RATE/intensity - MAP FROM WEATHERBELL

The most intense conditions are forecast for late Thursday morning into the afternoon. Two main corridors of concern are expected: Owen Sound to Collingwood off Lake Huron, and Wasaga Beach to Orillia off Georgian Bay. Snowfall rates will be exceptionally high, and the squalls could remain locked in place for 6–12 hours, leading to rapid accumulation.

Strong wind gusts during this period could result in blizzard conditions, with near-zero visibility on roads. Road and highway closures are likely in the hardest-hit areas, especially on Thursday.

By late Thursday night, the snow squalls may shift into the Bruce Peninsula and Muskoka regions. While the bands are expected to weaken by Friday morning, lingering activity could still produce scattered flurries before tapering off completely by the afternoon.

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As with previous lake-effect events, it’s important to remember that these snow squalls are highly localized. Narrow bands of snow, often only a few kilometres wide, can result in dramatically different conditions over short distances. One location might see over 50 cm of snow while areas just a few kilometres away remain relatively unscathed.

We currently have high confidence in two zones being hardest hit: southern portions of the Bruce Peninsula, including Owen Sound, Chatsworth, Meaford, and Flesherton, and areas west of Orillia, including Midland and Coldwater. Accumulations in these regions could exceed 50 cm, with totals potentially nearing 100 cm if squalls remain stationary long enough. A more conservative estimate is 50–75 cm.

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A wider swath of Grey-Bruce, including Kincardine, Port Elgin, Hanover, Lion’s Head, and Tobermory, as well as much of Simcoe County and northern portions of Kawartha Lakes, Gravenhurst, and Beaverton, could see 25–50 cm. Not all areas in this zone will hit these totals, as much depends on the placement and movement of the snow bands.

Further south and away from the snowbelt, accumulation decreases rapidly. Barrie itself may largely miss the snow, although it could see up to 25 cm if the bands shift slightly. The Georgian Bay squall may extend inland at times, bringing heavy snow to Lindsay and Peterborough, with 10–20 cm possible in these areas.

For regions in other parts of the snowbelt, including Muskoka, Parry Sound, Haliburton, and parts of Dufferin, Wellington, Perth, and Huron counties, totals are expected to range from 10–20 cm. The Golden Horseshoe, including London, Kitchener, and Guelph, will likely see only light flurries, with less than 5 cm expected.

'Ice Day' Forecast: Widespread School Bus Cancellations Likely on Tuesday in Central and Eastern Ontario

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Following Monday's freezing rain that brought icy conditions across Central and Eastern Ontario, the risk of freezing drizzle persists through the overnight hours.

Environment Canada has issued widespread freezing drizzle advisories, warning that the slick conditions could extend into early Tuesday morning. With temperatures remaining near or just below the freezing mark overnight, untreated surfaces are expected to stay icy well into the morning.

As a result, it’s likely that many school boards, particularly in rural areas, will opt to cancel school bus services on Tuesday morning due to the hazardous road conditions.

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The highest confidence for cancellations is in rural Eastern Ontario, where freezing drizzle is expected to still be occurring at the time decisions are made. These areas have been given a 90% chance of an “ice day.”

In the City of Ottawa, the likelihood is slightly lower at 75%, as the school board tends to be more conservative with cancellations in urban settings. However, the overnight icing should still be significant enough to prompt cancellations.

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In Central Ontario, the Parry Sound and North Bay region has the highest probability of cancellations at 90%. The school board in this area is typically more weather-sensitive, and the lingering freezing drizzle almost guarantees that buses will be cancelled.

The situation becomes more uncertain for Muskoka, Haliburton, and Kawartha Lakes. Here, the freezing drizzle is expected to taper off shortly after midnight, but icy road conditions are likely to persist into the morning, with temperatures remaining near freezing.

After Monday’s decision to proceed with buses in some areas backfired for Trillium Lakelands—forcing adjustments to afternoon routes—the school board is likely to exercise more caution on Tuesday to avoid similar issues.

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South and west of these regions, the chances of cancellations decrease significantly. Freezing drizzle is expected to end earlier in the evening, and temperatures are forecast to rise overnight, mitigating icy conditions. While cancellations cannot be entirely ruled out—particularly in Simcoe County—most other areas are unlikely to see disruptions to bus services on Tuesday.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

'Ice Day' Forecast: Freezing Rain Threatens to Cancel School Buses on Monday in Parts of Southern Ontario

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Freezing rain is forecast to impact parts of Central and Eastern Ontario starting Monday morning and continuing throughout the day.

With Environment Canada issuing freezing rain warnings that highlight potential road hazards on Monday, it is highly likely that many school boards in the affected regions will choose to cancel bus services as a precaution.

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The highest likelihood of an “ice day” is focused on areas northwest of the GTA, particularly in higher elevations, as well as regions around Lake Simcoe and into Eastern Ontario north of the Lake Ontario shoreline.

For school boards in these areas, there is a 75% to 90% chance of bus cancellations. While confidence in cancellations is high, there remains a small possibility that some boards might take a gamble due to the later expected start of the freezing rain. This uncertainty has kept the chances from being universally set at 90%.

The only area where we feel a solid 90% confidence level is the southern portion of the Tri-Board district. Historically, this region has been very proactive in response to any Environment Canada winter weather warnings, so the presence of a freezing rain warning is likely enough to prompt cancellations there.

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Further north, including Muskoka, Haliburton, and the Ottawa Valley, messy weather may not arrive until later in the day. As of now, Environment Canada has not issued freezing rain warnings for these areas, which lowers the likelihood of bus cancellations.

Probabilities range from 25% to 50%, with just a 10% chance in the City of Ottawa. Urban cancellations in Ottawa typically require more severe conditions, so the lower chance is consistent with their past responses.

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In contrast, Southwestern Ontario and the GTA are expected to see mainly rain with minimal freezing rain, making school bus cancellations in these regions highly unlikely.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

Prolonged Freezing Rain Threatens Icy Start to Week for Parts of Southern Ontario on Monday

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December has kicked off with a cold and snowy start across Southern Ontario, as a significant lake-effect snow squall outbreak blanketed parts of the snowbelt over the past week. This wintry weather was accompanied by the season's first blast of Arctic air, bringing wind chills as low as -20°C.

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However, a shift in the weather pattern is underway, with milder conditions already spreading into Southwestern Ontario, where Sunday saw daytime highs climbing into the mid to upper single digits.

A weather system is expected to arrive early Monday, bringing warmer air aloft, while near-surface temperatures hover around freezing. This setup creates ideal conditions for freezing rain across parts of Central and Eastern Ontario, which, according to the latest data, could last for an extended period.

Freezing rain is expected to begin in the morning hours on Monday, persisting through the afternoon and into the evening. This prolonged event could result in a thin but hazardous layer of ice forming on untreated surfaces such as roads, sidewalks, trees, and power lines, with localized power outages a possibility.

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The initial bands of precipitation will move into Deep Southwestern Ontario, including Windsor and London, during the pre-dawn hours on Monday. Temperatures in this region will remain several degrees above freezing throughout the day, so precipitation here is expected to fall as rain.

As the system progresses north and east during the morning, it will encounter below-freezing temperatures near the surface in areas like the Dundalk Highlands (including Orangeville and Shelburne) and parts of the Greater Toronto Area (GTA).

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This will result in the development of freezing rain, creating a zone stretching from Orangeville eastward through York Region, along the higher elevations of the Oak Ridges Moraine, and into southern portions of Central and Eastern Ontario.

This band of freezing rain is expected to persist into the early afternoon, with locations such as Barrie, Orillia, Kawartha Lakes, Peterborough, and Belleville likely experiencing the heaviest impacts.

Further north, areas like Muskoka, Bancroft, and the Ottawa Valley are expected to see a mix of wet snow, ice pellets, and freezing rain beginning early Monday afternoon. While significant snowfall accumulation is not expected for Southern Ontario, enough snow could fall to create slushy and slippery road conditions in these areas.

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Freezing rain will begin to taper off in the south later in the afternoon, though freezing drizzle may linger into the early evening. Temperatures are forecast to rise slowly above freezing later in the evening and overnight, which should help melt any accumulated ice, albeit gradually.

In more northern portions of Central and Eastern Ontario, heavier freezing rain will persist into Monday evening before ending overnight. However, freezing drizzle may continue in the Ottawa Valley into early Tuesday morning, potentially causing icy conditions for the Tuesday morning commute.

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The most significant freezing rain impacts are expected in a narrow corridor extending around Lake Simcoe and eastward along the Lake Ontario shoreline.

Ice accretion of 2 to 5mm is possible in areas such as Orangeville, Newmarket, Collingwood, Barrie, Orillia, Midland, Bracebridge, Lindsay, Peterborough, Oshawa, Belleville, and Kingston.

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For the rest of Central and Eastern Ontario, including the Ottawa Valley, up to 2mm of ice accretion is expected, accompanied by ice pellets and a few centimeters of wet snow.

In the GTA, the greatest impacts from freezing rain will likely occur in the northern and eastern portions of the region. Toronto may experience brief freezing rain during the morning hours, but it is expected to transition quickly to rain, especially closer to the lakeshore.

Fast Moving Clipper to Dump Up to 10-20cm of Snow on Parts of Ontario & Quebec This Weekend

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After a week dominated by seemingly endless snow squall activity across the snowbelt regions of Southern and Northern Ontario, the lake-effect snow machine is finally taking a break as we head into the first full weekend of December. However, this pause in squalls doesn’t mean the weather will be quiet for long!

We’re tracking a system originating from the Prairies that is expected to sweep across Ontario and Quebec between Saturday and Sunday. This fast-moving clipper will bring a widespread blast of snow, with accumulations ranging from 10 to 20 cm across Northern Ontario, Central and Eastern Ontario, and parts of Southern Quebec.

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Precipitation associated with this system has already begun moving into Northwestern Ontario from Manitoba and will continue spreading eastward through the overnight hours. Areas near the international border, including Fort Frances, may also see a risk of freezing rain. Light to moderate snow will develop around Lake Superior and into Northeastern Ontario by Saturday morning.

As Saturday progresses, the system’s first snow bands will push southward into parts of Southwestern, Central, and Eastern Ontario by the afternoon. Initially, snowfall is expected to be light but could reach areas within the Golden Horseshoe. A sharp cut-off in precipitation means Deep Southwestern Ontario and regions along the Lake Erie shoreline are likely to see little to no accumulation.

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By Saturday evening, the bulk of the precipitation will concentrate over Central and Eastern Ontario, where moderate to heavy snow will persist through the evening and into the early overnight hours.

Snowfall will taper off in Southwestern Ontario by the early evening and in the Greater Toronto Area by mid-evening. For the rest of Central and Eastern Ontario, snow will likely ease shortly after midnight, though areas closer to the Quebec border could see lingering snowfall into the pre-dawn hours.

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During this time, temperatures in Southern Ontario will gradually rise, pushing many locations above the freezing mark and resulting in a mix of rain and snow. Central and Eastern Ontario, however, are expected to remain cold enough to keep precipitation as all snow.

For Quebec, snowfall is forecasted to begin mid to late Saturday afternoon, with Montreal likely seeing its first snow bands just after dinner. Snow will continue through the overnight hours and is not expected to clear out until late Sunday morning.

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In terms of accumulation, this system is relatively straightforward compared to scenarios involving mixing or lake enhancement. Across Northern Ontario, a general 10 to 15 cm is expected, including areas such as Armstrong, Marathon, Wawa, Timmins, Chapleau, and Kirkland Lake. Isolated locations could see totals closer to 15 to 20 cm.

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Farther south, snowfall totals of 10 to 20 cm are anticipated across much of Central and Eastern Ontario and Southwestern Ontario east of Lake Huron. This includes regions such as Grey-Bruce, Orillia, Muskoka, North Bay, Sudbury, Peterborough, Kingston, and the Ottawa Valley. Similar accumulations are expected in Southern Quebec, including Montreal, where snowfall amounts of 10 to 15 cm are likely, with localized pockets nearing 20 cm.

Meanwhile, lower amounts are expected in areas such as London, Kitchener-Waterloo, the Niagara Region, and the western GTA, where snowfall totals will likely remain around 5 cm or less. Toronto, in particular, may see minimal accumulation due to limited moisture reaching the area as the system concentrates on Central and Eastern Ontario. Deep Southwestern Ontario will likely see only trace amounts.

'Snow Day' Forecast: Will London Area Students Ever Go to School? Likely Not Until Next Week!

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Intense snow squalls have developed off Lake Huron and Georgian Bay on Thursday, delivering significant snowfall to areas southeast of the lakes. This activity is expected to persist through the overnight hours, gradually weakening early Friday morning. However, snowfall totals in the hardest-hit regions are likely to exceed 50 cm by the time the squalls subside.

Given the expected heavy accumulation overnight, it is highly likely that some school boards in the affected regions will decide to keep buses off the roads for yet another day.

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The highest probability of cancellations will again be concentrated along the southeastern shoreline of Lake Huron. This includes the southern portion of the Avon Maitland District School Board (AMDSB) and the Thames Valley District School Board (TVDSB), which covers the City of London.

There is a 90% likelihood of bus cancellations in these areas, as the combination of the existing snowpack and additional overnight snowfall will almost certainly create treacherous travel conditions for the morning commute.

The remainder of the Lake Huron shoreline, including the northern section of the AMDSB, the entire Bluewater District School Board (BWDSB), and the “West” weather zone for the Simcoe County school board, has a 50–75% chance of cancellations.

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For school boards east of Georgian Bay, including the NNDSB (Parry Sound), Trillium Lakelands (Muskoka), and the “North” weather zone for Simcoe County, we have assigned a 50–75% chance of cancellations. Confidence here is slightly lower because the snow squalls in these areas are expected to intensify later in the day.

As mentioned in Environment Canada's snow squall watch, conditions will likely worsen in the afternoon, requiring school boards to make proactive decisions in the morning. This is particularly true for Parry Sound, where the school board has a history of erring on the side of caution when adverse weather is expected.

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Outside the snowbelt regions, the likelihood of a snow day is almost non-existent, as the heavy snow will remain highly localized to areas directly impacted by the squalls.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

London Area Could Get Hammered by Intense Snow Squall on Thursday With Locally Up to 50-75cm of Snow

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As the Alberta Clipper that brought widespread snowfall to Southern Ontario exits late Wednesday, snow squalls are set to return to the snowbelt regions. Unfortunately, the areas that were buried earlier this week will once again bear the brunt of this lake effect activity.

Locations just north and west of London appear to be in the bullseye, with the potential for 50 to 75 cm of fresh snowfall accumulation by the end of Thursday.

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Lake effect activity is expected to begin organizing overnight and into early Thursday morning along the southern shorelines of Lake Huron and Georgian Bay. Current forecasts suggest this activity will consolidate into a few well-defined snow squalls by late morning or early afternoon.

The most intense squall is projected to form off the southeastern shoreline of Lake Huron, extending from Port Franks through Strathroy and into the west end of London. Additional streamers could impact areas further inland and along the eastern Lake Huron shoreline, stretching from Kincardine down to Grand Bend.

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A separate squall will develop off Georgian Bay, spanning from Collingwood to Shelburne. Forecast models differ on the intensity of this squall, with some suggesting it could push far inland, potentially reaching parts of the Greater Toronto Area (GTA) just in time for the evening commute.

This scenario could bring a heavy burst of snow to the Hwy 400 corridor between Bradford and Vaughan, possibly extending to Mississauga and even the western parts of Toronto.

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The primary concern with this event is that the squalls are unlikely to shift much throughout the day. Instead, they could remain stationary for over 12 hours, beginning Thursday morning and continuing into the late evening.

As seen in Muskoka over the weekend, stationary squalls can produce extreme snowfall rates of 10–15 cm per hour, quickly overwhelming plowing operations and making travel nearly impossible as highways are buried in snow.

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Travel is strongly discouraged along the Lake Huron shoreline, particularly on Hwy 402 between London and Wyoming, during the day on Thursday and into the evening. Blizzard-like conditions, combined with rapid snowfall accumulation, will create dangerous and potentially life-threatening travel conditions.

The Georgian Bay squall is expected to diminish just after midnight, while the Lake Huron squall will gradually lift north of London during the pre-dawn hours on Friday. Additional lake effect snow is possible east of Lake Huron and Georgian Bay on Friday, though it remains unclear whether it will organize into significant squalls. We will provide updates in a separate forecast if substantial accumulation seems likely.

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The most intense snowfall is expected to target a small area west of London, including Parkhill, Ailsa Craig, and Strathroy, where totals could exceed 50 cm and potentially reach 75 cm. It’s important to note that these higher totals will be very localized, as the squall is forecast to be quite narrow. The exact location of the heaviest accumulation will depend on where the squall sets up.

While the City of London is likely to avoid the worst of the snowfall, it isn’t entirely in the clear. The city’s west end could see totals ranging from 25 to 50 cm. A slight eastward shift in the squall could place London directly in its path, significantly increasing snowfall totals for the area.

Lower amounts are expected in London’s east end, which is likely to see between 10 and 20 cm. St. Thomas could also be affected, with snowfall potentially reaching 20–30 cm depending on how far inland the squall extends.

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Other communities along the southeastern shoreline of Lake Huron, including Grand Bend, Lucan, Exeter, Clinton, and Goderich, are projected to receive 25–50 cm by the time the squalls diminish on Friday morning.

As is typical with snow squalls, snowfall gradients will be extremely sharp, and accumulation will drop off quickly outside the most affected areas. Locations such as Kincardine, Listowel, and Mitchell can expect totals of around 10–20 cm.

The Georgian Bay squall is anticipated to be less intense than its Lake Huron counterpart. Accumulations of 15–25 cm are expected for areas like Collingwood and Shelburne. If the squall extends into parts of the GTA, it could bring a quick 5–10 cm of snow, primarily affecting Brampton, Mississauga, and other areas in the western GTA.

Less than 5cm is expected for the rest of Southern Ontario.

'Snow Day' Forecast: Yet Another Chance of School Bus Cancellations on Thursday in Southwestern Ontario

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Snow continues to linger across Southern Ontario as of Wednesday evening, but it is expected to taper off as the system exits the province overnight. However, snow squalls are forecast to develop along the southeastern shorelines of Lake Huron and Georgian Bay, potentially creating hazardous travel conditions.

Environment Canada has issued widespread snow squall warnings, which could prompt some school boards to keep buses off the roads for yet another day.

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The highest probability of school bus cancellations is along the entire eastern shoreline of Lake Huron, including all regions within the Bluewater District School Board (BWDSB) and the Avon Maitland District School Board (AMDSB). This area is almost certain to experience a “snow day” on Thursday, with poor travel conditions making it difficult to see how buses could safely operate.

The Thames Valley District School Board (TVDSB), covering Middlesex, London, Oxford, and Elgin, also has a strong chance of cancellations, with probabilities ranging from 75% to 90%. The same applies to the Lambton zone of the Lambton Kent District School Board (LKDSB).

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Around Georgian Bay, there is a 75% chance of cancellations for the “West” weather zone of Simcoe County, where snow squall activity is expected to be most intense. The “Central” and “North” weather zones have a 50% chance, as it is less certain whether conditions will be severe enough to lead to cancellations.

To the east of Georgian Bay, the snow is expected to taper off overnight, offering a bit of a reprieve. However, the Parry Sound region still has a 50% chance of cancellations due to the potential for blowing snow, which could create hazardous conditions. This school board also tends to be particularly cautious when it comes to weather-related disruptions.

For the Muskoka region, there is a slight chance of cancellations. If schools do reopen, Thursday would mark the first day back for much of Southern Muskoka since last Thursday.

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For the rest of Southern Ontario, widespread cancellations are not anticipated. However, we have assigned a broad very low to low chance of cancellations across Eastern and Central Ontario, just in case blowing snow results in some unexpected disruptions.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

'Snow Day' Forecast: Heavy Snow on Wednesday May Cancel Some School Buses in Southern Ontario

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An Alberta Clipper is set to move into Southern Ontario early Wednesday, bringing the potential for 20-30 cm of snow in some areas. Snow squalls will also persist northeast of Georgian Bay, as well as near Lakes Erie and Ontario, during the morning hours.

The anticipated impact on Wednesday morning’s commute, combined with potential disruptions to the afternoon commute, will likely lead some school boards to cancel school buses. While there is still some uncertainty about how widespread these cancellations will be, certain areas have a higher probability of being affected.

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There is a 90% chance of a “snow day” for the Bruce Peninsula and areas northeast of Georgian Bay. This includes the entire Near North District School Board (NNDSB), which is known to be highly cautious regarding weather conditions. The expected snow squalls in these areas are likely to meet the criteria for bus cancellations.

For the rest of Central Ontario, parts of Eastern Ontario, and rural areas of Southwestern Ontario, the probability of school bus cancellations ranges from 50% to 75%. Confidence is slightly lower in these regions because much of the snow is expected to fall after morning cancellation decisions are made. Additionally, Environment Canada has gone with winter travel advisories, which may not carry enough weight for some school boards to cancel buses proactively.

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The likelihood of cancellations increases in areas forecasted to experience snow squalls or where blowing snow advisories are in effect. This includes regions along the shorelines of Lakes Huron, Ontario, and Erie, where reduced visibility and challenging travel conditions are expected.

In contrast, urban school boards in the Greater Toronto Area (GTA) are unlikely to cancel buses, as the forecasted conditions are not expected to meet the higher thresholds typically required for urban cancellations. We’ve assigned a slim 5-10% chance to account for the possibility of an unexpected decision by one of the boards, but this remains highly improbable.

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Similarly, Deep Southwestern Ontario—including Sarnia, Windsor, and Chatham—is unlikely to see school bus cancellations, as these areas are forecasted to receive less than 5 cm of snow from this system. Conditions there are not expected to be severe enough to warrant disruptions.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

Alberta Clipper to Bring a Snowy Blast to Southern Ontario on Wednesday With Up to 20cm Possible; Snowbelt Region Could See Up to 50cm

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The snowy landscape across Southern Ontario is quickly transforming as a multi-day snow squall event has blanketed parts of the snowbelt regions with over 100 cm of snow.

While the intense accumulation has primarily impacted areas around Lake Huron and Georgian Bay, the rest of Southern Ontario will soon have their turn as a weather system moves into the region on Wednesday.

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This system-related snowfall will likely combine with lake enhancement and embedded snow squalls, resulting in higher accumulations in the snowbelt areas that are still digging out from the weekend’s relentless snowfall.

By Thursday morning, some snowbelt regions could see an additional 30-50 cm of snow. Meanwhile, a general 5-15 cm of snow is expected across much of Southern Ontario, including parts of the Greater Toronto Area (GTA), which has experienced minimal snowfall so far this season.

The Alberta clipper responsible for this system began pushing into Northwestern Ontario from Manitoba on Tuesday afternoon. Moderate to heavy snow will continue spreading across Northern Ontario through the evening and overnight.

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In Northern Ontario, we expected the highest snowfall totals to be found east of Lake Superior stretching from Wawa down to Sault Ste. Marie. Snowfall totals of between 30 to 50cm are possible thanks to the system-related snowfall and snow squalls off Lake Superior.

Other areas around the Georgian Bay shoreline extending into Sudbury could be looking at around 20cm of snowfall accumulation. This will also be the case south of Lake Nipigon which could see some lake enhancement between Thunder Bay and Geardton.

The rest of Northeastern Ontario is looking at around 10 to 15cm with locally up to 20cm. Less than 10cm is expected for Northwestern Ontario including Thunder Bay.

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Ahead of the system, lake effect snow has already started to intensify, beginning with Lake Superior on Tuesday afternoon. By Tuesday evening, snow squalls are expected to organize off Lake Huron and Georgian Bay, primarily targeting the Bruce Peninsula and areas northeast of Georgian Bay, such as Parry Sound, Britt, and North Bay. These snow squalls are likely to persist through the night into Wednesday morning.

Additional lake effect snow could develop off Lake Erie and Lake Ontario during the early morning hours of Wednesday, potentially drifting into the southern Niagara region and Prince Edward County. While this activity may cause reduced visibility and locally heavy snowfall, the squalls are not expected to remain stationary for long, limiting overall accumulation.

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As the system reaches Southern Ontario around sunrise on Wednesday, the existing lake effect snow bands are expected to merge with the system’s light to moderate snowfall. This merging could enhance snow totals, particularly off the northern shorelines of Lake Erie and Lake Ontario. Narrow bands of heavy snow could stretch across the Niagara region and into parts of Central and Eastern Ontario, leading to significant variations in snowfall accumulations.

Snow totals will likely vary substantially due to localized banding caused by lake enhancement. Some areas may see only 5 cm, while nearby locations could receive 15-20 cm, depending on where the snow bands develop.

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Another key factor with this system will be strong wind gusts, ranging from 50-70 km/h across Southern Ontario, beginning Wednesday morning and continuing throughout the day. These winds, combined with steady snowfall, could create blowing snow and reduced visibility, making travel hazardous. With this being the first significant snowfall event of the season outside the snowbelt, drivers are urged to exercise caution.

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While the system is expected to exit Southern Ontario by late Wednesday, snow squall activity will persist off Lake Huron and Georgian Bay. An intense squall is projected to develop off Georgian Bay late Wednesday evening, stretching inland toward Midland, Orillia, and Gravenhurst, and continuing into the early hours of Thursday.

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By Thursday morning, shifting winds will push the Georgian Bay squall southward toward Collingwood and Angus. This squall may extend far inland at times, impacting the Highway 400 corridor between Vaughan and Barrie, as well as parts of the northern GTA. Meanwhile, a Lake Huron squall is anticipated to stretch from Goderich through Grand Bend and into the London area.

Significant snowfall could occur on Thursday if these squalls remain stationary for an extended period. Current models suggest they may not weaken until late Thursday night or early Friday morning, potentially producing intense snowfall rates for over 24 hours.

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Regarding snowfall totals, the uneven distribution caused by lake enhancement means localized accumulations will vary widely. The highest confidence lies in regions northeast of Georgian Bay, including Parry Sound, Sundridge, Britt, and North Bay, where 30-50 cm of snow is expected, with localized amounts possibly exceeding those totals due to snow squalls.

Surrounding areas, such as Muskoka and Orillia, could see 20-30 cm of snow by Thursday morning, accounting for system snow, lake enhancement, and snow squall activity. Similarly, areas east of Lake Huron could see totals ranging from 20-30 cm.

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In Central and Eastern Ontario, widespread snowfall is likely to range from 10-15 cm, except for the Ottawa Valley, where accumulations may be closer to 5 cm. Lake enhancement could push some areas along the northern shorelines of Lake Ontario and Prince Edward County closer to 20 cm.

For regions such as Kitchener, Woodstock, Guelph, and Barrie, snowfall totals are projected to reach 10-15 cm. However, variability due to lake enhancement may result in some areas seeing lower amounts. The GTA is expected to receive closer to 5 cm, while the Niagara region could accumulate 5-10 cm, with localized heavier bands of snow influenced by Lake Erie.

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In Deep Southwestern Ontario, snowfall amounts will decrease westward, with London forecasted to receive around 10 cm. Further southwest, including Sarnia, Windsor, and Chatham, totals are expected to remain under 5 cm.

It’s important to note that these totals do not account for the snow squalls expected to impact areas southeast of Lake Huron and Georgian Bay beginning Thursday morning. High-resolution models are still refining the locations of these squalls, but additional accumulations of 30-50 cm are possible in affected areas. Stay tuned for a detailed update in a separate forecast.

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'A Conveyor Belt of Snow’; How Lake Effect Snow Can Bury Entire Towns in a Matter of Days

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satellite image of lake effect snow over the Great Lakes, courtesy of the national weather service.

Following the incredible snowfall seen in Sault Ste. Marie and across parts of Muskoka over the weekend, we figured this would be the perfect opportunity to discuss lake effect snow. It’s something that many of us in Ontario have come to expect in the late fall and early winter, especially since we’re surrounded by the Great Lakes.

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Certain ingredients are required for lake effect snow to occur, but most importantly, there needs to be an unfrozen body of water and a very cold air mass from the Arctic.

In order for lake effect snow to even start to form, there needs to be a temperature difference of at least 13°C between the warm surface of the lake and the 850mb pressure level of the atmosphere (this is typically found at around 1500 metres). The greater the temperature difference, the more unstable the atmosphere becomes and this is often when we see strong convection and the phenomenon known as thundersnow. Without this difference in temperature, lake effect snow simply can not occur. Once this threshold is reached, however, it’s like a switch being flipped and the lake effect snow machine starts.

Another key component in lake effect snow development is moisture. Ideally, the relative humidity at the surface needs to be at least 80% for lake effect snow to form and levels below 70% could actually inhibit development. It can usually be assumed that the lake itself can provide enough moisture, but this is not always true. There also needs to be limited wind shear with height between the surface and the 700mb pressure level so that the moisture is more focused, sort of like a hose. The strongest, most organized bands of lake effect snow develop when the wind shear is less than 30°.

Finally is the concept known as “fetch”. Yes, millennials, we’re trying to make fetch happen. Fetch is the distance that the air mass travels over the lake. Fetch needs to be at least 100km in order for lake effect snow to develop and the greater the fetch, the more snow is produced. When considering prevailing wind directions, the traditional snowbelts are found in areas that are downwind of the greatest possible fetch over the Great Lakes, i.e. Buffalo and the entire length of Lake Erie.

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The creation of lake Effect Snow. Courtesy of Environment Canada.

When all of these conditions are met, we can see how lake effect snow actually develops.

As the cold air mass travels over the much warmer surface of the lake, the warmth and moisture from the surface is transferred into the lower atmosphere. The warmer, moister air rises and it eventually cools and condenses, forming narrow bands of clouds. These clouds continue to travel over the open lake, gathering even more moisture, until they eventually reach land and the snow starts to fall at rates that can easily exceed 5cm per hour and could even be as high as 20cm per hour! It’s important to note that the hardest hit areas are actually not found immediately at the shoreline, but rather 30-50km inland from the lake.

The direction of the winds dictates which areas are hit by the lake effect snow so as long as the ideal conditions continue, so too will the development and subsequent falling of lake effect snow. This could lead to several days of heavy snow hitting the same area while there are sunny skies less than 20km away. A slight shift in wind direction can quickly change which area gets hit and that makes lake effect snow notoriously tough to forecast.

'Snow Day' Forecast: Tuesday Is Likely to Bring Another Round of School Bus Cancellations in Southwestern Ontario

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The seemingly endless potential for snow squalls is set to persist through Monday evening and into Tuesday morning. This round will primarily affect the eastern and southern shorelines of Lake Huron, where an additional 10 to 25 cm of snow is expected overnight. These conditions will likely lead to more school bus cancellations in areas already impacted on Monday.

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.Meanwhile, the cleanup continues in the Muskoka region following the intense snow squalls that dumped over 100 cm of snow on Bracebridge and Gravenhurst over the weekend. The Trillium Lakelands District School Board has announced that ONLY schools in Gravenhurst will remain closed on Tuesday, while buses serving the Bracebridge area will not be running.

Schools and transportation services in Huntsville will operate as usual. We’ve marked this region as "Already Cancelled" on our map, as the school board rarely issues sub-regional cancellations. For precise details, check the official announcement linked here.

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For weather-related cancellations elsewhere, the strongest likelihood of a "snow day" is in AMDSB (Exeter), with a 90% probability due to expected intense snowfall accumulation overnight.

Surrounding areas, including BWDSB (Southampton and Kincardine), AMDSB (Goderich and Stratford), TVDSB (Middlesex and London), and LKDSB (Lambton), have a 50/50 to strong chance of school bus cancellations, as these regions could see notable snowfall and challenging travel conditions.

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There’s also a 50/50 chance of cancellations in BWDSB (Meaford) and the "West" weather zone of Simcoe County due to potential snow squall activity off Georgian Bay. However, there is less confidence in whether the snowfall will be intense enough to disrupt transportation.

For the rest of Southern Ontario, school bus cancellations on Tuesday are unlikely. That said, attention is already shifting to Wednesday, as a developing weather system could bring widespread snowfall accumulation, with the potential to significantly impact some areas.

This may lead to school bus cancellations midweek. Stay tuned for our ‘snow day’ forecast on Tuesday afternoon!

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.

'Snow Day' Forecast: Widespread School Bus Cancellations Likely on Monday Around Lake Huron and Georgian Bay

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Intense snow squalls continue to pound the snowbelt regions surrounding Lake Huron and Georgian Bay, persisting through the weekend and expected to last into Monday. Environment Canada has issued widespread snow squall warnings, forecasting an additional 30 to 50 cm of snow by Tuesday.

Given these conditions, it seems highly likely that many school boards in the hardest-hit areas will cancel buses on Monday morning. Travel will remain hazardous throughout the day, making it nearly impossible to operate school buses safely.

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The highest confidence for cancellations lies along the Eastern Lake Huron and Southern Georgian Bay shorelines, affecting boards like AMDSB (Goderich and Exeter) and BWDSB (Kincardine and Meaford). In these regions, there is a 90% chance of a "snow day" on Monday.

For Trillium (Muskoka), there’s also a 90% likelihood of cancellations. While no significant additional snowfall is expected overnight, the extensive cleanup from previous snowfalls and the continued closure of the major highway in the region will likely make bus travel unfeasible.

UPDATE (6:15 PM): Trillium Lakelands DSB has announced that schools in the Muskoka region will be closed on Monday.

Similarly, NNDSB (Parry Sound) and Trillium (Haliburton) face potential cancellations, but with lower probabilities of 50% and 25%, respectively, as these areas were not as severely impacted.

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Surrounding areas, including TVDSB (Middlesex), AMDSB (Stratford and Listowel), BWDSB (Southampton, Owen Sound, and Hanover), and the "West" weather zone for Simcoe County, have a 75% chance of seeing buses canceled due to lingering squall activity and ongoing poor travel conditions.

Outside the core snowbelt regions, the likelihood of cancellations decreases significantly. For the "North" and "Central" weather zones in Simcoe County, there’s a 50/50 chance of a snow day. While the brunt of the lake-effect snow is expected to remain closer to Georgian Bay, Environment Canada’s snow squall warnings could still prompt precautionary cancellations.

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The chances are also 50/50 in London and Oxford County, where snow squall activity is less certain to intensify enough to justify cancellations. Urban boards like these often have higher thresholds for cancellations compared to rural regions.

For the remainder of Southern Ontario, school bus cancellations are unlikely, as the worst conditions are expected to remain confined to the typical snowbelt areas.

Disclaimer: Instant Weather has zero authority when it comes to bus and school closures. It is completely up to the school boards, bus companies, local authorities, and parents to decide what is best for their children. This is our best guess based on our forecast.