Southern Ontario: School Bus Cancellations and Closures for Tuesday, November 11, 2025

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Cancellation & Closure Map (English Public and Catholic Schools)

Please note: School board boundaries are a rough estimate. Don’t use this map to determine what school board or weather zone you live in as accuracy isn’t guaranteed.

• Green = No Cancellations

• Red = Cancellations (Click for More Details)

• Purple = School Closures (Click for More Details)

List of Cancellations & Closures

English Public and Catholic Schools

• Avon MaitIand Public & Huron-Perth CathoIic: There are several cancellations, please visit this link for more details: https://hpsts.mybusplanner.ca/Alerts

• BIuewater Public & Bruce-Grey Catholic: ALL buses CANCELLED into Meaford & Thornbury. There are several additional cancellations, please visit this link for more details: https://www.mybrucegreyschoolbus.ca/Cancellations.aspx

• Dufferin-PeeI Catholic: Buses to St. Andrew, St. Peter, St. Benedict as well as Dufferin County buses to Robert F. Hall CSS are cancelled today

• Lambton Kent Public & St. CIair Catholic: Buses in Zones 1 & 4 Cancelled Today

• Thames Valley Public & London CathoIic: Busses in Middlesex and Elgin are cancelled and the schools in these regions are closed.

• Tri-Board: Transportation is cancelled in Tri-Board’s North Hastings, North & Central Lennox & Addington, North, Central & South Frontenac weather zones today.

• Upper Grand Public & Wellington CathoIic: All school taxis and buses in Dufferin County will not be operating today.

French Schools

• Conseil scolaire catholique Providence: Middlesex region (rural roads): Transport is cancelled today. City of London routes are operating. Lambton Region Zones 1 & 4 are cancelled. Busses for Meaford are cancelled.

• Conseil scolaire Viamonde: Middlesex region (rural roads): Transport is cancelled today. City of London routes are operating. Lambton Region Zones 1 & 4 are cancelled. Busses for Meaford are cancelled.

‘Snow Day’ Forecast: Snow Squalls Likely to Cancel School Buses in Southern Ontario’s Snowbelt on Tuesday

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/11/11/bus-cancellations

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

Snow squalls continue to hammer portions of Southern Ontario tonight, particularly off the southeastern shores of Lake Huron and Georgian Bay. These squalls are producing bursts of heavy snow, whiteout conditions, and rapidly changing visibility across many areas. Travel remains extremely difficult in the hardest-hit zones, and reports continue to come in of near-zero visibility and snow quickly piling up on untreated roads.

The snow machine is far from done. These intense squalls are expected to persist through the overnight hours and into Tuesday morning. As winds shift slightly eastward, the heaviest activity may drift toward London, the southern half of Huron County, and even as far east as Barrie and northern Simcoe County.

Given these conditions, Tuesday morning is shaping up to be a challenging one for school transportation in the Lake Huron and Georgian Bay snowbelts. It’s difficult to imagine buses being able to safely operate in some of these areas with such intense, localized bursts of snow and blowing snow expected to continue right into the morning.

The highest likelihood for bus cancellations will be found in regions such as Sarnia-Lambton, Middlesex, London, Exeter, Stratford, and Listowel, extending into parts of Grey-Bruce, including Meaford and Owen Sound.

These areas fall directly under the snow squall bands and have been dealing with heavy accumulation and treacherous driving conditions since Monday. We’re assigning these regions a 75 to 90 percent chance of cancellations, depending on how the squalls align overnight.

Surrounding regions, including Chatham-Kent, Elgin, Oxford, and Simcoe Central, could go either way. These areas may see lighter snow at times, but if a squall shifts slightly in their direction early Tuesday, it could quickly turn things around. For that reason, we’ve placed them around the 50 percent mark, essentially a coin flip for a snow day.

Outside of the core snowbelt, the risk for bus cancellations drops off sharply. However, there’s still a 25 percent chance for some northern GTA communities, as the Georgian Bay squall could extend farther south or east for brief periods overnight, bringing bursts of snow to places like Newmarket or northern York Region.

The Niagara region also deserves a mention. Some lake enhancement from Lake Ontario could add to snowfall totals there, though the extent remains uncertain. For now, we’re giving Niagara a slight chance of cancellations, mainly due to potential early morning slick conditions if snow bands drift farther inland.

Elsewhere across Southern and Eastern Ontario, we’re not expecting any widespread cancellations. That said, because snow squalls are notoriously unpredictable, even areas outside the main snowbelt can occasionally see quick bursts of snow that lead to surprise disruptions. For most of the GTA, though, this is likely just a regular Tuesday, so don’t count on a snow day just yet.

All in all, the best odds of getting that coveted day off from school are in the traditional snowbelt zones near Lake Huron and Georgian Bay. For everyone else, it’s back to class, but with winter tires and a little extra caution on the morning commute.

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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.

Southern Ontario: School Bus Cancellations and Closures for Monday, November 10, 2025

**Please refresh your page every few minutes to receive the latest update**

Cancellation & Closure Map (English Public and Catholic Schools)

Please note: School board boundaries are a rough estimate. Don’t use this map to determine what school board or weather zone you live in as accuracy isn’t guaranteed.

• Green = No Cancellations

• Red = Cancellations (Click for More Details)

• Purple = School Closures (Click for More Details)

List of Cancellations & Closures

English Public and Catholic Schools

• Kawartha Pine Ridge Public & Peterborough Victoria Northumberland Clarington Catholic: Due to storm aftermath and reported slippery/icy road conditions all transportation is cancelled today for Northumberland, Clarington, Peterborough City and County.

• Renfrew County Public & Renfrew County Catholic: Zone 4 Madawaska area transportation services ONLY are cancelled due to road conditions.

• Tri-Board: Transportation is cancelled in Tri-Board’s Lennox & Addington, Frontenac, and Kingston weather zones today.

French Schools

• Conseil des écoles publiques de l’Est de l’Ontario (CEPEO): Transportation is cancelled for Kingston

• Conseil des écoles catholiques de langue française du Centre-Est: Transportation is cancelled for Kingston

• Conseil catholique MonAvenir: Busses are cancelled for Peterborough

Snow Squalls Could Bury Parts of Southern Ontario’s Snowbelt in Up to 50cm of Snow Early This Week

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As much of Southern Ontario cleans up after our first widespread snowfall of the season, Mother Nature is showing no signs of slowing down. The lake effect snow machine is roaring to life over Lake Huron and Georgian Bay as we kick off the second week of November.

Snow squalls have already developed south of Lake Huron late Sunday evening and are expected to strengthen through the night. We’re also anticipating some squall development along the southern shoreline of Georgian Bay, which should organize by Monday afternoon or evening.

Two main regions are likely to see the most intense activity. The first stretches between Sarnia and London, while the second includes areas south of Georgian Bay from Blue Mountain and Meaford toward the west of Barrie. Both zones could see heavy snow squalls lasting through to Tuesday morning.

While snowfall totals will vary significantly across short distances, confidence is increasing that the hardest hit areas could see as much as 25 to 50cm by the time the squalls taper off on Tuesday. Localized pockets may even exceed 50cm, depending on where the heaviest bands set up.

Road conditions are expected to deteriorate quickly in these regions, with road and highway closures likely late Monday and into early Tuesday when the most intense squalls occur. Travel should be avoided unless absolutely necessary, as these bands can produce sudden whiteouts, making it nearly impossible to see the road ahead.

ESTIMATED AIR TEMPS AROUND 1.5KM ABOVE GROUND - MAP FROM WEATHERBELL

This setup is being fueled by a rare November appearance of a mini “Polar Vortex” which is pulling a blast of Arctic air into Southern Ontario. This cold air is flooding the upper levels of the atmosphere and setting the stage for intense lake effect activity.

To put it simply, when forecasters talk about 850mb temperatures, we’re referring to the air temperature roughly 1.5 kilometres above the ground. This level helps forecasters understand how cold the air mass is higher up in the atmosphere, which is critical for predicting lake effect snow.

Over the next few days, 850mb temperatures are expected to plunge into the negative teens. Lake effect snow forms when there’s a large temperature difference between the lake surface and the air above it, generally 13°C or greater. With upper air temperatures between -10°C and -15°C and lake temperatures still above 10°C, that difference is more than 20°C, creating ideal conditions for lake effect snow to thrive.

hourly snowfall rates (cm) - MAP FROM WEATHERBELL

As of midnight, snow has already developed off the southern shores of Lake Huron, impacting the Sarnia region. So far, the bands have been disorganized and spread out, but that’s expected to change by late Monday morning as a stronger, more focused squall forms somewhere between London and Sarnia.

While the exact placement remains uncertain, areas near Petrolia and Strathroy appear most likely to be in the direct path. The band will likely shift through the day as wind directions fluctuate, leading to varying snow intensities across nearby towns.

hourly snowfall rates (cm) - MAP FROM WEATHERBELL

By Monday evening, things will really start to ramp up. The main squall off Lake Huron will likely push inland, with a more northwesterly wind direction steering it toward Grand Bend, Goderich and potentially the western edges of London. It’s still unclear if the squall will reach directly into London or remain just outside the city, but if it does, the heaviest snowfall will likely fall on the west side.

Meanwhile, snow squalls are expected to organize over Georgian Bay with heavy snow bands developing between Owen Sound and Barrie. There’s still some disagreement among models, with some focusing more on Wasaga Beach and Barrie while others favour a southern shoreline setup.

An interesting twist could occur if these Georgian Bay bands extend far enough inland to be enhanced by Lake Ontario. In that case, snow could reach into the western GTA and even the Niagara region, leading to sudden bursts of heavy snow if everything aligns.

hourly snowfall rates (cm) - MAP FROM WEATHERBELL

This lake effect activity is expected to persist overnight and into Tuesday morning, though the Georgian Bay bands should weaken slightly around sunrise. West of London, however, heavy snow could continue well into Tuesday morning before breaking apart as conditions become less favourable later in the day.

As always with lake effect snow, totals are extremely difficult to pinpoint. These narrow bands can stay locked over one community for hours while completely missing another just a few kilometres away. One person may end up shovelling half a metre of snow while someone nearby barely sees a dusting.

That said, two areas consistently stand out across the latest model runs. One includes Lambton Shores, Grand Bend and Strathroy, while the other covers the southern Georgian Bay shoreline and higher terrain around Blue Mountain. These regions could see totals ranging from 25 to 50cm by Tuesday.

Surrounding communities such as Petrolia, Thamesville, St. Thomas and Lucan, along with Orangeville, Shelburne and Flesherton, are more likely to see 15 to 25cm.

Both London and Barrie sit right on the edge between lighter and heavier accumulations. We currently have them in the 5 to 15cm or 15 to 25cm zones, depending on how far east the snow squalls extend.

Finally, the Niagara region remains uncertain. If the Georgian Bay squalls stretch far enough inland and connect with Lake Ontario, parts of the region could pick up over 15cm of additional snow.

Outside of these snowbelt regions, impacts will be much less significant. A few flurries and brief bursts of snow are possible as the squalls wobble, but most areas outside the direct lake effect zones should remain relatively calm through Tuesday.

‘Snow Day’ Forecast: Southern Ontario’s First Wintery Blast May Lead to School Bus Cancellations on Monday

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/11/10/bus-cancellations

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

A system swept through Southern Ontario on Sunday, bringing with it the first widespread accumulating snowfall of the season. For many, this was the first real taste of winter, and it certainly didn’t hold back. As the system pushes eastward, snow is beginning to taper off in most regions Sunday evening, though parts of Eastern Ontario will continue to see flakes fly past midnight before conditions gradually improve Monday morning.

While the timing of this system makes it less likely to cause major issues for the Monday morning commute, there is still a chance that some regions could see school bus cancellations. The main concern will be how quickly local and rural roads can be cleared before buses head out early in the morning. Road crews will be busy overnight, but areas that received the heaviest snow or where snow continues into the early hours may still be playing catch-up by dawn.

Adding to the challenge, lake effect snow is expected to fire up behind the main system as early as Monday morning and persist through Tuesday, particularly around Lake Huron and Georgian Bay. Environment Canada has issued snow squall watches for these areas, mentioning the potential for 15 to 30 cm of additional snow, with locally higher amounts possible under stronger squalls. This could lead to sudden drops in visibility and rapidly changing travel conditions.

Because of this, some school boards near the lakes may choose to cancel buses proactively, especially where snow squall watches remain in effect. However, confidence in widespread cancellations is lower at this stage since the heaviest lake effect snow isn’t expected to fully develop until later Monday morning or afternoon.

Based on the forecast and our past experience, the highest chance for a “snow day” is across rural Eastern Ontario, particularly the Frontenac region within the Tri-Board area. We’re giving this region around a 75% chance of cancellations. Snow is expected to linger longest here, and these rural routes are typically slower to clear. The rest of the Tri-Board area, along with the Upper Canada and Renfrew regions, could go either way, earning a 50% chance depending on how quickly road conditions improve by morning.

The City of Ottawa, on the other hand, is less likely to see a snow day. Urban areas tend to handle these events better, and the overall snowfall amounts aren’t expected to reach the threshold that usually triggers cancellations. Still, we’ve placed Ottawa at a 25% chance, since it’s the first major snowfall of the season and even modest totals can cause delays if cleanup efforts fall behind overnight.

Across Southwestern Ontario and the Lake Huron snowbelt, bus cancellations are also possible, especially as snow squalls intensify through the day. School boards such as LKDSB, TVDSB, AMDSB, and BWDSB could see anywhere from a 50% to 75% chance of cancellations, depending on where the lake effect bands set up. The heaviest and most persistent squalls are expected along and just inland from the shoreline, particularly around Grand Bend, Strathroy, and Petrolia. The Simcoe West and Meaford areas could also be affected by Georgian Bay lake effect activity, where we’ve assigned a 50% chance.

Outside of Eastern Ontario and the lake effect zones, the risk of a snow day drops off significantly. Most of the Golden Horseshoe, Niagara, and Southwestern Ontario should have more than enough time for roads to be cleared before the morning commute.

That said, temperatures will dip below freezing overnight, which could cause refreezing of slushy or untreated surfaces and create localized icy patches. Even where cancellations aren’t expected, drivers should plan for slower travel Monday morning.

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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.

Snowy Sunday Sweeps Into Southern Ontario With First Widespread Snowfall of the Season

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While there has been a lot of uncertainty surrounding Southern Ontario’s first widespread snowfall event of the season, we’re finally starting to get a clearer picture of what will unfold on Sunday. After several model shifts over the past few days, the latest data is now coming into better alignment, giving us a more confident idea of how this system will behave.

A developing low-pressure system is expected to move in from the southwest late Saturday night, tracking across areas near Lake Erie through the day on Sunday. As it does, it will bring a broad swath of snow stretching from Windsor through the Golden Horseshoe and into Eastern Ontario. Snow is expected to last much of the day before gradually tapering off overnight.

At this stage, snowfall totals are expected to vary quite a bit across the region. The exact placement of the heaviest snow bands remains uncertain, and surface conditions will also play a big role. Since the ground is still relatively warm, some of the early snowfall may melt on contact before it can begin to accumulate, especially on roads and sidewalks.

In general, by Monday morning, snowfall totals are expected to range from around 5 to 10 cm across the Golden Horseshoe and into Eastern Ontario. Within those areas, localized pockets, particularly in Eastern Ontario, could pick up as much as 15 to 20 cm according to the latest model runs. Further north and west, across Central and Southwestern Ontario, amounts will be lower with less than 5 cm expected in most spots.

As the system departs, colder air will pour into Southern Ontario late Sunday night, sending temperatures well below freezing. Any slushy snow or water on roads, sidewalks, and driveways will freeze quickly overnight, which could create slick conditions for the Monday morning commute. Drivers should be prepared for icy patches, and there’s a decent chance of school bus cancellations in areas that see higher snowfall totals.

The colder air will also fire up the lake effect snow machine early next week. Model guidance suggests that an intense but narrow band of snow could form southeast of Lake Huron late Monday and continue into Tuesday. This could impact communities such as Grand Bend and London, where local snowfall totals could exceed 25 cm if the band remains stationary for an extended period.

PRECIP TYPE - MAP FROM WEATHERBELL

For timing, snow is expected to begin in Deep Southwestern Ontario shortly after midnight. Around Windsor and Chatham, it may even start as rain before transitioning to snow as temperatures drop closer to dawn.

PRECIP TYPE - MAP FROM WEATHERBELL

By late Sunday morning, the snow will have spread into the Golden Horseshoe, becoming heavier through the afternoon. In Eastern Ontario, snow will likely begin around Kingston early in the morning and reach the Ottawa area by midday.

hourly snowfall rates (cm) - MAP FROM WEATHERBELL

The heaviest snowfall rates across the Golden Horseshoe are expected from early to mid-afternoon, with some models projecting bursts of 2 to 4 cm per hour at times before tapering off toward the evening.

PRECIP TYPE - MAP FROM WEATHERBELL

For Eastern Ontario, steady snow will continue through the afternoon, peaking after dinner before easing into scattered flurries overnight. With that timing, school bus cancellations are quite possible for parts of Eastern Ontario on Monday.

There are also some indications that freezing rain or ice pellets may mix in along the international border Sunday evening. Areas such as Kingston, Brockville, and Cornwall are most at risk for this brief mix, which could add an extra layer of slickness to untreated surfaces.

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

While there is still some disagreement among the models on exactly where the heaviest snow will fall, the general expectation remains 5 to 10 cm along the Golden Horseshoe and into Eastern Ontario, with some locally higher amounts near 15 cm.

We’ve outlined portions of Eastern Ontario and the higher elevations of the Niagara region on our map with a dotted zone, representing areas that could overachieve and see closer to 20 cm. However, that outcome is far from certain.

Keep in mind that this is the first significant snowfall of the season, and with ground temperatures still above freezing, actual accumulation could vary from one street to the next. Some areas may see a quick coating, while others struggle to hold the snow through the day, especially near the lakeshores.

Elsewhere, Southwestern Ontario and much of Central Ontario should see lighter amounts, generally only a few centimetres, with some localized areas possibly reaching up to 8 cm. Regions like Grey-Bruce and the northern parts of Central Ontario will likely miss out on the heaviest snow this time, but that may not last long as lake effect activity ramps up early next week.

PRECIP TYPE - MAP FROM WEATHERBELL

As higher-resolution models continue to come into range, we’re getting a clearer idea of what the first snow squall event of the season could look like. Current projections suggest activity will develop on Monday, with a more organized squall forming by the evening.

This band may set up somewhere between Grand Bend and Kettle Point, extending inland, likely just west of the City of London. Additional bands may also develop off Georgian Bay, impacting areas around Meaford and Collingwood.

Communities caught under these narrow squalls could see impressive snowfall totals, while just a few kilometers away, grass may still be visible. We’ll continue to refine the details as the event approaches and will have a more specific forecast on who could see the most snow closer to Monday.

Overall, this marks the true start of the winter season across Southern Ontario, with several systems and lake effect events lining up behind this one. It’s a good time to check that your winter tires are ready, snow shovels are handy, and morning routines include a few extra minutes to clear off your car. Winter is here to stay.

What's in a Name? Choosing the Right Tires to Drive you Through Canadian Winters

Tread patterns of summer, all season and winter tires. Image courtesy of discount tire.

Now that it’s the first week of November, many Canadians are starting to think about putting winter tires on their vehicles. There have been pockets of unseasonable warmth across the country in October and with it now being the start of November, the inevitable chill of winter is in the air, and many have already seen snow fall.

While winter tires are recommended throughout the country, they are mandatory in Quebec from December 1st to March 15th, and from October 1st to April 30th on certain British Columbia highways. Additionally, studded tires are allowed almost nationwide, with the exception of residents of Southern Ontario.

Insurance companies across the country offer discounts for installing winter tires as an incentive to encourage drivers to reduce the risk of accidents. So what makes winter tires that much better in the cold and snow than summer tires and where do all season and all weather tires fit into the mix?

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With the right tools, it can be pretty easy to change your own tires!

Summer Tires

Summer tires are designed to handle both wet and dry road conditions with their wide tread and soft rubber. These tires also usually have deeper grooves that improve traction on wet roads and reduce hydroplaning, making them ideal for the wet spring and summer months.

Winter Tires

Like their name suggests, winter tires have been designed for winter roads. They are made with rubber that stays flexible at temperatures below 7°C (45°F), the magic number at which other tires become stiff and lose traction, greatly reducing their performance. Furthermore, winter tires have different tread patterns that are meant to divert water and slush to the sides, as well as little slits called sipes that increase the overall grip of the tires and helping them maintain contact with icy road surfaces. Over the past several years, tire manufacturers have started to include additional small particles, like crushed glass or walnut shells, that act as little studs on the surface of the tire for extra grip.

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Performance of All Season Tires vs Winter Tires with decreasing temperatures. Image courtesy of Discount Tire.

All Season & All Weather Tires

Some people argue that winter tires aren’t necessary if they have all season tires on their vehicle. Unfortunately, this is a slight misnomer because while these tires can handle a bit of cold and snow, they fail to handle heavier snowfalls that are common in Canadian winters. All season tires, unfortunately, sacrifice traction in wet conditions that would be found in summer tires and some of the flexibility and grip seen with winter tires in order for the tread to last longer. Realistically, these should be called 3 season tires as opposed to all season. So while they’re not the best option for winter driving in Canada, all season tires are definitely a better choice than regular summer tires.

All weather tires, not to be confused with all season tires, are a true year-round tire designed to handle Canadian winters. Unlike all season tires, these tires remain soft and flexible well below 7°C. The tread pattern on all weather tires is a combination of all season and winter tires, making them better suited for driving through heavier snow than all season tires. While they still don’t match the performance of a true winter tire, all weather tires are the best option for those who don’t want the hassle of swapping out their tires twice per year or simply do not have the space to store an extra set. Their versatility truly makes all weather tires a middle of the road tire (pun intended) for Canadian drivers.

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The three-peak mountain snowflake symbol found on winter and all weather tires. Image courtesy of Canadian tire.

When looking for tires to get you through the winter, it is recommended to chose either a proper winter tire or an all weather tire, so long as it has the three-peak mountain and snowflake symbol on the sidewall. This is an industry standard symbol which indicates that the tire meets strict regulations for winter performance; becoming mandatory on all winter tires beginning in 2018, transitioning away from just using the M+S (Mud and Snow) designation.

Note: The author formerly received payments from “Big Tire” however, this article was not funded.

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Further Reading

https://www.canadiantire.ca/en/how-to/automotive/how-to-choose-winter-tires.html

https://www.continental-tires.com/ca/en/tire-knowledge/winter-tire-laws-in-canada/

https://www.continental-tires.com/ca/en/tire-knowledge/winter-tire-markings/

https://www.discounttire.com/learn/tires-below-45

https://www.discounttire.com/learn/winter-summer-allseason

Southern Ontario to Plunge Into Winter as Sunday Snowstorm Could Dump Up to 20 cm of Snow

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It feels like just yesterday we were talking about record-breaking heat that stretched well into October. But November has been a completely different story, with winter now making its presence known across Southern Ontario. Those warm late-autumn days are coming back to haunt us, as the still-warm lakes are setting the stage for a series of snowy chances in the days ahead, including the lake effect snow machine coming to life.

Cold Arctic air is set to flood into the province, bringing several snowmakers with it, including a potential snowstorm on Sunday, followed by intense snow squalls early next week.

Our first system arrives on Friday, spreading across Ontario throughout the day. Southern Ontario will mainly see rain from this one, while Northern Ontario braces for a significant dumping of snow. Some areas could see close to 20 cm by Saturday.

As colder air rushes in behind this system, temperatures will plunge across Southern Ontario through Saturday night. By Sunday, much of the region will be below freezing, setting the stage for the next system expected to move in during the day Sunday. Early indications suggest that parts of Southern Ontario could see significant snowfall from this system, with totals possibly reaching up to 20 cm by Sunday night.

That said, there’s still plenty of uncertainty surrounding the exact track of the storm. A slightly more southern route could pull the heaviest snow into the Greater Toronto Area as colder air dips farther south.

PRECIP TYPE - MAP FROM WEATHERBELL

The first round of precipitation will begin in Northwestern Ontario late Thursday, spreading across Northeastern and Southern Ontario by Friday morning.

RAINFALL TOTALS - MAP FROM WEATHERBELL

For most of Southern Ontario, this will mean a steady rainfall, with totals around 5 to 10 mm, although localized pockets near the lakes could see closer to 15 mm.

SNOWFALL TOTALS - MAP FROM WEATHERBELL

Higher elevations in Central Ontario, including Algonquin Park, could see some wet flurries mix in at times. Farther north, around Hearst, Kapuskasing, Cochrane, and Timmins, it’s all snow, with totals of 15 to 20 cm possible by Saturday morning.

TEMPS - MAP FROM WEATHERBELL

Behind the system, much colder air will spill into Central Ontario overnight Friday into Saturday, dropping temperatures well below freezing. The rest of Southern Ontario will see the chill arrive soon after, with most regions seeing their daytime highs recorded just after midnight Saturday before temperatures tumble through the day.

TEMPS - MAP FROM WEATHERBELL

By early Sunday morning, the cold will be firmly in place. Most areas will be below freezing, except for parts of Deep Southwestern Ontario and along the Lake Ontario shoreline where temperatures will hover just above zero.

PRECIP TYPE - MAP FROM WEATHERBELL

This cold setup will pave the way for Sunday’s incoming system. Models are in disagreement about the storm’s path, which will ultimately decide who gets the heaviest snow. The American and Canadian models track the low across Lake Erie and Lake Ontario, placing the rain-snow line near the GTA.

In this scenario, areas north of the GTA, including parts of Southwestern Ontario, Lake Simcoe, and the Ottawa Valley, would see heavy snow, while the GTA experiences a mix of rain, ice pellets, and wet snow.

PRECIP TYPE - MAP FROM WEATHERBELL

Even a small shift southward, as suggested by the European model, would change everything. That track takes the low through Pennsylvania and Upstate New York, shifting the heaviest snowfall into the GTA and surrounding regions, with totals over 15 cm.

SNOWFALL TOTALS - MAP FROM WEATHERBELL

In this case, the snow would stretch from London through the GTA, Peterborough, and into Ottawa, while Central Ontario and Grey-Bruce see lower amounts.

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

For now, most models favour the northern track, so that’s what we’re leaning toward in our preliminary forecast. But if the European solution proves right, those snowfall zones could shift south before the final forecast is issued.

Under the current setup, the heaviest snow is expected across a broad stretch of Southwestern Ontario, including the Lake Huron shoreline through Kitchener and up toward Barrie, Lindsay, and Peterborough, extending into the Ottawa Valley. These areas could see 10 to 15 cm of snow, with localized pockets near 20 cm possible.

The American NAM model is even more aggressive, suggesting up to 30 cm in some areas, though that’s likely overdone. The London area, GTA, and Eastern Ontario fall into a mixing zone, with 5 to 10 cm possible once precipitation switches to snow. Should the system shift farther south, those totals could increase.

Farther south, places like Windsor, Chatham, Sarnia, and the Niagara Region are expected to stay mostly rain, though a slushy 5 cm of snow is possible.

Snowfall will taper off by late Sunday, but the story won’t end there. Behind the storm, a strong surge of cold air over the still-warm Great Lakes will ignite a burst of lake-effect snow squalls on Monday.

The exact regions that will see the most intense squalls remain uncertain until higher-resolution models come into range, but areas downwind of Lake Huron and Georgian Bay should prepare for the potential of significant accumulations. Some communities could be digging out from 25 cm or more by early next week.

Snowy Scare: Frightful Flurries May Haunt Parts of Southern Ontario on Halloween Night

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After a soggy start to Halloween Eve across Southern Ontario on Thursday, a strong system will cast a gloomy spell over the region with widespread rainfall. But don’t be fooled, as that’s only a taste of what Mother Nature has brewing in her cauldron for Halloween itself.

Last year, we were treated to a mild and friendly Halloween with temperatures that felt more like a trick than a treat. This year, however, it looks like Halloween will send a real shiver down your spine as temperatures drop to levels more fitting for the undead.

Rain from Thursday is expected to linger overnight and into the early hours of Friday, heavy at times, especially across Eastern Ontario. The good news is that the worst of the rainfall should clear out just in time for trick-or-treating across Southwestern Ontario and the Golden Horseshoe. Temperatures will hover around what’s normal for this time of year, ranging from the mid to upper single digits, possibly reaching the low double digits in Deep Southwestern Ontario.

But it’s as if a witch has placed a chilling curse over Central and Eastern Ontario. As the rain lingers through Friday, some areas could begin to see strange white shapes drifting through the sky and no, they aren’t ghosts! These spooky apparitions are far more real, as rain could turn to wet flurries as early as Friday afternoon. Cold air will creep in like a Halloween fog, sending temperatures tumbling toward the freezing mark by evening.

While there’s some disagreement between models (a classic case of meteorological mischief), there’s solid agreement that a wide stretch of Central Ontario may experience at least a few wet flurries on Halloween night.

Where the models differ is in timing and intensity. Some are quite aggressive, conjuring an earlier and more widespread switchover to snow that could even allow for light accumulations in higher elevations. Others show a less frightful outcome, with flurries limited to the hills and highlands later in the day as the rain fizzles out elsewhere.

PRECIP TYPE - MAP FROM WEATHERBELL

As we rise on Halloween morning, rain will still be haunting much of Southern Ontario, though it will begin to taper off from west to east.

That’s where the great model split begins. For this forecast, we’re focusing on the NAM (American) and HRDPS (Canadian) models, which represent two distinct camps. The European model seems to be siding with the Canadian solution.

The American model pulls colder air into Central Ontario faster, dropping temperatures a few degrees lower than the Canadian model. It might not sound like much, but when temperatures hover near freezing, every degree counts. This could allow snow to start mixing in by early afternoon.

Areas like Algonquin Park, Haliburton, Bancroft, and northern Muskoka may see the first flurries, with the “mixing zone” spreading south through the afternoon into Muskoka, northern Simcoe County, and the Kawartha Lakes region.

PRECIP TYPE - MAP FROM WEATHERBELL

The Canadian model delays the switchover until closer to dinnertime, mainly over higher elevations.

By then, the precipitation in western areas may already be fading, keeping Muskoka and Simcoe County mostly rain-soaked rather than snow-covered.

PRECIP TYPE - MAP FROM WEATHERBELL

If the American model’s spookier version plays out, several hours of heavy, wet snow could fall Friday evening. While the ground is still warm, we’ve seen before that a strong enough burst of snow can briefly overcome that warmth and start to accumulate.

This model also spreads the snowy risk zone further east, even hinting at flakes creeping into the Ottawa Valley.

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The most likely areas to see actual snow include the higher elevations of Central Ontario, such as Sundridge, Huntsville, Algonquin Park, and Bancroft. These regions could even pick up a few slushy centimetres by night’s end if the stronger scenario comes true.

Elsewhere across Central Ontario, including Parry Sound, Bracebridge, Orillia, Kawartha Lakes, Tweed, and Pembroke, some wet flakes could mix in as trick-or-treaters prowl the streets. Accumulation isn’t expected here as the ground remains too warm, but it might add an extra eerie touch to the evening.

ESTIMATED PRECIP OVER LAST 3 HOURS - MAP FROM WEATHERBELL

As the ghosts, goblins, and ghouls hit the streets after nightfall, Southwestern Ontario will enjoy the calmest conditions, with rain clearing out hours earlier.

Central and Eastern Ontario, however, may not be as lucky. Light rain or even a few flurries could continue into the early evening, adding some spooky atmosphere to the night.

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For the prime trick-or-treating hours, Deep Southwestern Ontario will be the mildest, with temperatures around 8 to 12°C at 8 PM. Elsewhere across the Golden Horseshoe and Eastern Ontario, temperatures will settle into the mid to upper single digits.

The chilliest readings will haunt Central Ontario, where places like Muskoka, Algonquin Park, and Bancroft may see readings near the freezing mark with flakes swirling through the air. Those heading out should make sure their costumes have a few extra layers because this Halloween, it’s not just the monsters giving people chills.

Have a Happy Halloween!

Southern Ontario Turns Chilly With a Chance of Early Season Flurries for Some Areas Friday Morning

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The feeling of change is definitely in the air across Southern Ontario this week. Fall colours are now past their peak in many areas, and a noticeable chill has taken hold across the region. The arrival of cooler air, combined with the still-warm Great Lakes, has kicked off another round of lake-effect precipitation off Lakes Erie, Ontario and Huron.

While it’s still warm enough to keep most of that precipitation as rain, the traditional “snow belt” east of Lake Huron and Georgian Bay will continue to see periods of lake-effect rain through Thursday and into Friday. Local rainfall totals of 25 to 50 mm are possible by Friday, especially east of Lake Huron.

However, not everyone will escape a touch of wintry weather this week. The latest model data suggests that temperatures could dip close to the freezing mark across parts of Central Ontario late Thursday night into early Friday morning. With some lingering showers still moving through the region, a few areas could see those showers briefly mix with wet flurries before sunrise on Friday.

The best chance to spot the first flakes of the season will be across Northern Muskoka (including Huntsville and Sundridge), Algonquin Park, Bancroft and North Bay. That said, precipitation will be very scattered, and not all of these locations will see snow. Even if flakes do fall, they won’t stick around for long as the ground remains too warm and temperatures will quickly climb above freezing later in the morning.

ESTIMATED TOTAL RAINFALL BY FRIDAY - MAP FROM WEATHERBELL

For those near Lake Huron and Georgian Bay, Thursday looks to be a wet one. Bands of lake-effect rain are expected to develop overnight Wednesday and linger through the day Thursday. As is typical with lake-effect events, rainfall totals will vary greatly over short distances depending on where the bands set up.

These bands are expected to wobble around through Thursday into Friday, spreading precipitation over a broader area rather than locking in on one spot. If one of the stronger bands does remain stationary for an extended time, localized flooding could occur, particularly near Kincardine and Goderich where some models show up to 50 mm of rainfall possible by Friday.

The lake-effect setup off Georgian Bay isn’t expected to be quite as strong, but parts of Simcoe County around Collingwood, Wasaga Beach and Barrie could still see locally up to 25 to 50 mm of rain. Again, the highest amounts will be very localized.

Elsewhere across Southern Ontario, expect occasional showers Thursday with generally less than 10 mm of rain as the heaviest precipitation remains confined to areas near the lakeshores.

By Friday morning, precipitation will gradually taper off as conditions become less favourable for lake-effect activity.

ESTIMATED AIR TEMPERATURE on friday morning - MAP FROM WEATHERBELL

Overnight Thursday into Friday, temperatures will drop into the low single digits across much of Southern Ontario, with some Central Ontario communities dipping to near or just below freezing.

PRECIP TYPE - MAP FROM WEATHERBELL

While it’s not the first time this fall that temperatures have touched the freezing mark, what’s different this time is that lingering precipitation from both the lake-effect activity and a system over Quebec could overlap with those cold temperatures.

If any precipitation develops overnight, it could easily fall as wet flurries given the near-freezing surface temperatures and even colder air aloft that would favour snow instead of rain.

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It’s worth noting that models disagree on how much precipitation will actually be present on Friday morning. Some may be underestimating light, scattered precipitation, which means there’s a chance flakes could be seen as far south as Huntsville and Bancroft. The most likely region for these flurries remains around North Bay and Algonquin Park, where multiple models consistently show light snow.

Unless you’re up early Friday morning, you’ll likely miss the brief appearance of the season’s first flakes. Any snow that does fall will melt quickly once temperatures climb above freezing, and no travel impacts are expected.

Comparing the Loudest Weather Phenomena: Thunder, Tornadoes, Hail & Ice Quakes

we did ‘trivia time’ on our social media pages with this question and a huge thank you to all those who participated!

Comparing the Loudest Weather Phenomena

When the weather turns wild, it’s not just the winds and rain that grab our attention, the sound can be deafening! From a crackling thunderclap to the roar of a tornado, certain meteorological events push the boundaries of what our ears can handle. Below, we compare four of the loudest natural phenomena and how their peak volumes stack up.

photo credit: Brandon Morgan

Thunder: Nature’s Cannon

When lightning superheats the air, it produces a shockwave that we hear as thunder. A nearby strike can hit about 120 dB at ground level, about as loud as a rock concert or jet engine. Right near the lightning channel, sound pressure can briefly reach 165–180 dB, and rare “superbolts” may push that volume even higher. Fortunately, these extreme levels are localized; even a very strong strike a mile away typically registers in the 110–120 dB range.

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PHOTO CREDIT: GREG JOHNSON TORNADOHUNTER.CA

Tornado: The Freight Train Roar

Survivors often compare a tornado’s roar to a freight train. Typical sound levels near a tornado fall in the 90–100+ dB range, loud enough to make conversation impossible. At very close range, the loudest tornadoes may reach the 120 dB neighbourhood, rivaling a thunderclap or jackhammer. Direct measurements are scarce because no one wants to place microphones in an EF5’s path, but theoretical analyses speculate that peak levels could exceed this. In practice, a violent tornado’s roar can still cause physical pain or hearing damage if you’re near it and especially if it’s destroying trees, buildings, etc.

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PHOTO CREDIT: Marcel Strauß

Hail on a Metal Roof: Weather’s Drum Solo

On a calm day, rain on a metal roof is just background noise but hail can turn your home into a drum! Even small hailstones can bump the sound to 80–100 dB in an attic or shed. In extreme cases, especially when large hail combines with hurricane‑force winds, noise levels can rival thunder. A remarkable example is the 1986 Kansas/Missouri derecho, where large hail driven by 100 mph winds created a sustained roar around 120 dB, essentially as loud as a rocket engine. Baseball‑sized hail can still hit the 100+ dB range despite modern roofing and insulation.

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PHOTO CREDIT: CHATGPT AI IMAGE OF WHAT A FROST QUAKE MIGHT LOOK LIKE

Ice Quake: Frost’s Explosive Secret

Also known as cryoseisms, ice quakes occur when a sudden deep freeze causes waterlogged ground to fracture. They’re unpredictable and highly localized but witnesses describe the noise as a sharp boom or explosion that can shake a house. Precise decibel measurements are rare, yet anecdotal accounts suggest they can easily exceed 100 dB, on par with a thunderclap. During the January 2014 polar vortex, numerous frost quakes around Toronto woke residents with house‑shaking blasts. While the shaking may be minor, the sound is startling and intense.

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Which is the Loudest?!

All four of these weather phenomena can produce sound levels capable of causing hearing damage. Thunder regularly reaches around 120 dB and as mentioned above, superbolts may push this even higher. Tornadoes and massive hailstorms can come close to matching thunder’s intensity, especially at close range. Ice quakes aren’t as well-documented but the explosive nature of frost cracking suggests similar levels. Only extreme events like volcanic eruptions or meteor impacts significantly exceed these volumes. Regardless of the source, any sustained sound above 85 dB can harm your hearing over time.

In summary:

• Thunder: 110‑120 dB from a mile away; near the lightning can reach 165‑180 dB and superbolts may be higher.

• Tornadoes: Typically in the 90‑100+ dB range; violent tornadoes may approach 120 dB.

• Hail on a metal roof: Small hail can be 80‑100 dB; large hail plus ~100 mph winds can roar around 120 dB.

• Ice quakes: Unpredictable frost quakes with booms that witnesses estimate above 100 dB.

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And the winner is…

The winner, based on the available data and estimated volumes by experts; thunder from a superbolt lightning strike!

To help confirm our research, we spoke with our friend Dr. Dave Sills, Director of the Northern Tornadoes Project (NTP) and he agrees that the winner is likely a superbolt lightning strike, which has the potential to reach volume levels in excess of 180db. Ouch!

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Sources:

• NOAA & scientific literature on thunder acoustics en.wikipedia.orgfactsjustforkids.com; Earth Science Stack Exchange summary on superbolt thunder earthscience.stackexchange.com.

• Tornado sound estimates from anecdotal accounts and fun-fact compendiums facebook.com; theoretical energy calculations for F5 tornado noise stevemeadedesigns.com.

• Hail noise measurements from a 1986 storm report (Storm Data) glenallenweather.com; hail sound range from Q&A resources brainly.com.

• Descriptions of frost quakes from the USGS and science news reports usgs.govsnexplores.org.

STORMY SUNDAY: Parts of Ontario Could Experience Damaging Wind Gusts & Flooding Risk This Weekend

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Environment Canada has released its latest medium range forecast, highlighting the potential for 70-90km/h damaging wind gusts across Southwestern Ontario, the Niagara regions and western GTHA regions on Sunday, October 19th, 2025.

They also mention a rainfall risk for Northeastern Ontario with the potential for 30-60mm of accumulation that could cause isolated flooding.

If this trend continues towards the weekend, it’s certainly possible that the ‘minor’ risk will be increased to a ‘moderate’ risk but seeing as we’re still four days out, it makes sense that Environment Canada is keeping the risk at the minor level.

Environment Canada does have a specific explanation for minor risks and it is: “This weather event is potentially significant or of interest. Users should stay informed.”

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💨 Southern Ontario

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Environment Canada writes in their forecast for Southern Ontario:

“Strong southwesterly winds with gusts of 70 to 90 km/h are likely for areas near Lake Erie and portions of southwestern Ontario. Winds will shift to northwesterly with the passage of a cold front late in the day, with gusts up to 90 km/h possible. Confidence is low regarding the timing and strength of winds expected.”

They also break down the risks:

Hazard(s): Wind

Location: Southwestern Ontario and western portions of the Greater Golden Horseshoe.

Timing: Sunday

Impact(s): Broken tree branches and downed trees. Power outages likely.

Confidence: Low (1 out of 4)

Impact: Moderate (2 out of 4)

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🌧️Northeastern Ontario

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Here are Environment Canada’s details for the rainfall risk in Northeastern Ontario:

”Significant rainfall is expected, with rainfall amounts of 30 to 60 mm likely. Confidence is low regarding the exact location of heaviest rainfall at this time.”

They also break down the risks:

Hazard(s): Rain

Location: Portions of northeastern Ontario.

Timing: Sunday

Impact(s): Possible flooding in low-lying areas.

Confidence: Low (1 out of 4)

Impact: Moderate (2 out of 4)

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🔎 Staying Safe and Prepared

As we move towards the winter months, it’s critical to stay informed! To keep a close eye on our latest forecasts and get notified of any alerts, download our free app Instant Weather, available on Apple and Android devices.

Take a moment to secure any loose outdoor items before the storms arrive. Things like patio furniture, trampolines, and garbage cans can become projectiles in strong winds.

If you're planning to be on the roads, be prepared for challenging driving conditions such as sudden downpours, significantly reduced visibility, and the possibility of water pooling on roadways, especially in areas expecting heavier rainfall.

Stay safe everyone and if it’s safe to do so, share your reports with half a million community members on our Facebook group called Ontario Storm Reports!

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Disclaimer: These forecasts are issued by Environment Canada and typically published via their Twitter/X accounts. We receive these forecast via a daily email and often publish them to help inform our communities.

Autumn’s Grand Finale: Ontario Hits Peak Fall Colours This Thanksgiving Weekend

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If you’re spending the Thanksgiving Weekend in Ontario, you’re in for a treat as the fall colours are now peaking across much of the province! From Central Ontario to the Niagara Escarpment and parts of Southwestern Ontario, this weekend will showcase some of the best fall scenery of the season.

Over the past week, colour change has surged in many areas across Central, Eastern, and Southwestern Ontario, bringing that classic explosion of red, orange, and gold to the forests. For many regions, this weekend marks the perfect time to take a drive, hike, or just relax outdoors surrounded by nature’s best display.

Parks like Forks of the Credit, MacGregor Point, Sauble Falls, The Massasauga, Frontenac, and Murphys Point are all sitting at or near peak colour levels, with coverage between 70 and 90 percent. These areas are glowing with rich maple tones, offering stunning backdrops for family gatherings and Thanksgiving photos.

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Check out our new fall colour park dashboard that lets you track the fall colour change for each provincial park!

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However, farther north, the colours are starting to fade. Northern sections of Central Ontario, including Algonquin, Arrowhead, and Bonnechere has reached their peak several weeks ago, and the recent rain on Friday has accelerated leaf drop in those regions.

In fact, Mikisew Provincial Park has become the first location to officially move out of peak season, with around 80 percent leaf fall now reported. Many of these northern parks are still worth visiting, but visitors can expect more bare branches mixed with patches of remaining colour.

The transition southward is now well underway, with vibrant hues starting to spread into the Golden Horseshoe and Lake Erie shoreline regions. Bronte Creek, Turkey Point, and Point Farms are now showing brilliant orange and yellow tones, while Rondeau and Wheatley continue to progress slowly, likely about one to two weeks away from their peak.

For those in the GTA, Niagara, and Prince Edward County, this weekend should deliver plenty of colour and comfortable weather for outdoor plans.

THANKSGIVING WEEKEND WEATHER FORECAST

The good news is that the Thanksgiving Weekend forecast looks mostly favourable for outdoor activities; however, there will be a few areas of rain to work around.

ESTIMATED TOTAL RAINFALL ON SATURDAY - MAP FROM WEATHERBELL

Saturday will start off on a cloudy and damp note for many, especially across Central Ontario and portions of the GTA. Some scattered precipitation is expected during the morning and early afternoon hours, with the chance for locally heavier pockets of rain near the northern shores of Lake Ontario, between Toronto and Cobourg. Rainfall amounts could reach 10 to 15 mm in those localized zones.

Don’t let that discourage your plans, though, as the rain will be scattered and not persistent, and most areas should begin to dry out later in the day. By Saturday afternoon and evening, conditions will improve across Southern Ontario, while some lingering showers may persist just north of Lake Ontario.

Sunday looks to be the best day of the long weekend. Forecast models show mostly dry and mild weather, perfect for any outdoor Thanksgiving plans or fall colour tours. A few isolated showers could develop in Niagara or Far Eastern Ontario, but these should be brief and light.

ESTIMATED AIR TEMPERATURE on SATURDAY - MAP FROM WEATHERBELL

After a cool and damp Friday, temperatures on Saturday will hover right around seasonal values, with daytime highs in the low to mid-teens. Which is about what you’d expect for early to mid-October. It’ll feel crisp, but not unpleasant, especially once the rain clears.

ESTIMATED AIR TEMPERATURE on sunday - MAP FROM WEATHERBELL

On Sunday, slightly warmer air returns. Temperatures will rise into the upper teens, with some areas possibly touching 20°C or a bit higher in parts of Southwestern Ontario. It’ll be a comfortable, mild day overall, great for hiking, apple picking, or those traditional family dinners outside if you’re lucky enough to have a sunny patio.

Monday, Thanksgiving Day itself, should feature similar conditions to Sunday with a mix of sun and clouds, and daytime highs again in the upper teens or low twenties.

FINAL THOUGHTS

This Thanksgiving Weekend will likely offer one of the most colourful backdrops in recent memory across much of Southern Ontario. With so many regions now at or near their fall colour peak, and comfortable weather expected through much of the weekend, it’s the perfect time to get outdoors and soak in the season.

If you’re heading north, expect a more subdued scene with leaves already past peak. But if you’re staying closer to home in the GTA, Niagara, or Southwestern Ontario, you’re right on time to experience the full brilliance of Ontario’s fall foliage.

Grab your camera, take a drive down a country road, or plan a hike through one of Ontario’s provincial parks. The combination of crisp air, golden forests, and warm afternoon sun makes this Thanksgiving one to remember.

Enjoy the beauty, and Happy Thanksgiving from all of us at Instant Weather!

Get Your Shovels Ready: Ontario's Snowbelt Could Be Buried Again This Winter

Satellite image from GOES-16 shows lake effect snow coming off the Great Lakes on February 29th, 2024. Courtesy of CSU/CIRA & NOAA.

The summer of 2025 was a hot one in Southern Ontario, in which we saw high temperature records consistently broken throughout the region. This trend has continued into October, with temperatures surpassing 30°C in parts of Southwestern and Eastern Ontario during the first weekend of the month.

Despite the fact that we’re gradually moving into the coldest part of the year, the heat from the summer and fall will continue to impact local weather conditions this winter. This will be particularly evident as lake effect snow, a phenomenon that occurs every year in the late fall and early winter in Southern Ontario.

The two main ingredients necessary for the development of lake effect snow are a large unfrozen body of water and a very cold air mass. The air mass needs to be at least 13°C colder at the 850mb pressure level of the atmosphere (this is typically found at around 1500 metres) than the temperature of the surface of the water. Once this threshold is reached, it’s like a switch being flipped and the lake effect snow machine starts.

There is more to the development of lake effect snow than just cold air and an open body of water. 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”, which 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.

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

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. In Southern Ontario, lake effect snow typically hits areas to the east of Lake Huron and Georgian Bay, but it can also impact communities to the north of both Lake Erie and Lake Ontario.

Surface Temperature of Lake Huron throughout 2025 plotted with the 30 year average. Courtesy of NOAA CoastWatch.

So how does a hotter-than-average summer impact lake effect snow? To put it simply, a warmer summer leads to warmer lakes. Looking at Lake Huron, the main source of lake effect snow in Southern Ontario, the surface water temperature is approximately 2°C warmer than the 30 year average.

One of the important properties of water is its high heat capacity, which means that lakes heat and cool slower than the surrounding land. The warmer lakes will take longer to freeze, meaning that the lake effect snow machine can run even longer.

The current surface temperatures across the Great Lakes are very similar to last year at the same time. Many will remember last fall when the Muskoka Region was buried after several days of intense lake effect snow, trapping people in their homes and cars after the highways were closed.

This trend continued through most of the winter due to large expanses of open water remaining present in the Lakes. This was particularly the case in Bruce, Grey, and Huron Counties, where consistent lake effect snow resulted in massive snow piles and drifts that were up to 12 feet tall! The amount of snow also had an effect on local schools, with more than 30 snow days announced for students of some school boards.

Surface temperatures of the Great Lakes as of October 7th, 2025. Courtesy of Noaa Coastwatch.

Surface temperatures of the Great Lakes as of October 6th, 2024. Courtesy of NOAA Coastwatch.

While it is still too early to predict exactly how much snow will fall and where over the coming months, it is looking likely that we can expect a considerable amount of lake effect snow like last year.

Fall Colours Reaching Their Peak Just in Time for Thanksgiving Weekend for Much of Southern Ontario

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It’s shaping up to be a picture-perfect Thanksgiving Weekend across Ontario, and nature is putting on one last spectacular show before winter sets in. Across much of the province, the fall colours are now reaching their peak, just in time for the long weekend and this year’s display is one you won’t want to miss.

If you’ve been waiting for the ideal time to hit the road for a scenic fall drive, this is it. Central and Eastern Ontario are bursting with colour right now, with brilliant reds, oranges and yellows covering the forests from Muskoka to the Ottawa Valley.

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Check out our new fall colour park dashboard that lets you track the fall colour change for each provincial park!

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Parks such as Algonquin, Arrowhead, Bonnechere, The Massasauga, Silent Lake, and Bon Echo are all reporting colour change at or above 70 percent. The rich mix of maples and birches is producing a stunning contrast that paints the landscape with fiery autumn tones. For many areas, this is the absolute peak which is that magical window when most trees are fully changed but still hold plenty of leaves.

However, that window is short-lived. Some parks are now reporting more than 50 percent leaf fall, meaning these vibrant views won’t last much longer. If you’re planning a trip to Algonquin or other northern parks, this weekend could be your last chance to experience the full canopy before winds and cooler nights strip the trees bare.

Even with the ongoing leaf fall, the colour coverage across Central and Eastern Ontario remains exceptional. Parks including Frontenac, Voyageur, and Mikisew are glowing with late-season golds and deep reds, offering some of the best hiking conditions of the year. Clear skies and mild temperatures will make it easy to spend the whole day exploring the great outdoors.

While the north is beginning its gradual slide past peak, Southern Ontario is just getting started. From the Niagara Escarpment to the Lake Huron shoreline, and stretching east through Prince Edward County and the GTA, colour change is advancing quickly. Many of these regions are now sitting between 40 and 60 percent colour change, which means peak fall colour conditions are expected to line up perfectly with Thanksgiving Weekend.

That’s welcome news for anyone planning outdoor gatherings or day trips over the long weekend. Whether it’s a drive through the Dundas Valley, a picnic at Forks of the Credit, or a stroll through Rondeau or Bronte Creek, the next few days should feature stunning scenery and warm sunshine.

ESTIMATED AIR TEMPERATURE on sunday - MAP FROM WEATHERBELL

The latest high-resolution model data even suggests we’re in for another burst of summer-like warmth across Southern Ontario. On Sunday, temperatures are forecast to climb into the mid to upper twenties, with some inland areas possibly reaching the 30°C mark.

It’s a rare treat for early October and more like something out of August than Thanksgiving Weekend. For those closer to the lakeshores, expect slightly cooler highs in the lower twenties thanks to the lake breeze. Still, it’ll be a gorgeous day for a fall road trip, with plenty of sunshine and mild winds making for ideal driving conditions.

The warm weather will also help extend the life of the remaining leaves, giving the region a few extra days of brilliant colour before cooler air and rain return later next week. So if you’ve been putting off that annual fall colour tour, now’s your moment.

For the best viewing experience this weekend, head toward higher elevations in Central and Eastern Ontario, where the mix of tree species and cooler nights has created the most vibrant hues. Algonquin Provincial Park remains the top spot for photographers and nature lovers alike, with Arrowhead, Bonnechere, and Silent Lake close behind.

Those staying closer to home in Southern Ontario will still be rewarded with spectacular views. The rolling hills around Caledon, Mono Cliffs, and Hockley Valley are quickly transforming into a patchwork of gold and crimson. In Niagara, the escarpment trails and vineyards are beginning to glow, creating a perfect backdrop for Thanksgiving festivities.

Don’t forget about Prince Edward County, where fall colours are blending beautifully with the region’s scenic farmland and wineries. Areas like Sandbanks and Presqu’ile are starting to see that golden shift as maples and oaks catch up to their northern cousins.

As always, timing is everything when it comes to fall colour chasing. While many areas will look their best this weekend, winds or rain later in the week could quickly thin out the foliage. Keep an eye on local forecasts if you’re planning to travel, and be ready to head out early in the morning for the best light and least crowded parks.

So charge up your camera, roll down the windows, and take in every view, because before long, those vibrant trees will trade their fiery tones for the bare branches of late fall. Enjoy the show while it lasts, and have a wonderful Thanksgiving Weekend surrounded by the best of Ontario’s autumn beauty.

⛈️ Strong Severe Thunderstorm & Tornado Risk For Ontario on Thursday Evening

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The summertime heat we’ve been experiencing is about to fuel some potentially strong thunderstorms in Ontario on Thursday, July 24, 2025. The main risk is in the evening and overnight hours but some areas could see strong storms in the afternoon as well, especially in Northeastern Ontario.

Some of these storms, particularly from the Bruce Peninsula and east towards Muskoka, Algonquin and potentially through parts of eastern Ontario may see a strong damaging wind storm (MCS), which is showing up on several high-resolution models. The timing looks to be late afternoon into the evening and overnight as it moves east towards Quebec.

Across other parts of Ontario, there is a risk for a cluster or line of storms from as far south as Essex County, all the way up to northeastern Ontario in the late afternoon into the overnight hours. Some models suggest it could arrive in the late afternoon but quite a few are suggesting the storms won’t arrive for most of us until the evening or overnight, especially in the east.

Damaging wind gusts, potentially exceeding 100km/h+, large hail, torrential rainfall with isolated flooding and frequent lightning are the main risks. We’re also seeing the potential for a few isolated tornadoes with this system, especially in orange (3) zone on the forecast map.

STAY AHEAD OF THE STORM

Join us on YouTube as we track any storms that develop on Thursday. Make sure to hit the free Subscribe button and the notification bell icon to get notified when we go live!

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In the image above, Environment Canada has issued their forecast for Thursday, highlighting all of the southwestern, central, golden horseshoe and eastern Ontario regions in a 2/4 “Moderate weather threat”.

Below is a regional breakdown based on Environment Canada’s forecast details:

📍 Location A: Portions of Southern & Northeastern Ontario

Hazards: 🌬️ Wind, 🌨️ Hail, 🌧️ Rain, 🌪️ Tornado, ⛈️ Thunderstorms
Timing: Afternoon and evening

Impacts:

• 🪁 Loose objects may be tossed

• 🏚️ Damage to weak buildings

• 🌳 Broken tree branches and downed trees

• 🌿 Possible damage to plants and crops

• 🌊 Flash flooding and pooling on roads

• ⚡ Power outages likely

Rainfall: Up to 50 mm

Confidence: Moderate
Impact: Moderate

Details:
Storms may bring wind gusts up to 100 km/h, rainfall up to 50 mm, hail up to 2 cm, and the potential for isolated tornadoes. Activity begins in the northwest and tracks southeastward through the day.

📍 Location B: Portions of Southwestern & Eastern Ontario + Greater Golden Horseshoe

Hazards: 🌬️ Wind, 🌧️ Rain, ⛈️ Thunderstorms
Timing: Late afternoon and evening

Impacts:

• 🌳 Broken tree branches and downed trees

• 🌊 Flash flooding and pooling on roads

• ⚡ Possible power outages

Rainfall: Up to 50 mm

Confidence: Moderate
Impact: Moderate

Details:
Scattered thunderstorms may produce wind gusts up to 90 km/h and locally heavy rainfall.

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More details ASAP about this storm risk. Stay safe on Thursday, folks!

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And a big thanks to the sponsor of this forecast; Kempenfest in Barrie! For those who don’t know, our own Adam Skinner will be performing at Kempenfest this year with his new rock band ‘Face The Lion’! They’ll be opening for the one and only Colin James on Saturday, August 2nd!

Here’s some more details on Kempenfest:

”Kempenfest presented by TD, is Barrie Ontario’s signature festival event, celebrating 53 years Aug 1-4, 2025, located across two-kilometres of Barrie’s beautiful waterfront. The annual event is one of Ontario’s largest waterfront festivals, featuring 300 arts & crafts vendors, a midway, community village, antiques, face painters, buskers, great food, a poutine village, and two stages of live music! Evening concert headliners include Shawn Desman, Colin James, The Washboard Union, and The Practically Hip, with many more!”

We hope to see you there!

Ottawa Area, Eastern Ontario in Bullseye for Thursday’s Widespread Severe Storm & Tornado Risk; Isolated AM Risk for Southwestern Ontario & GTHA

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The oppressive heat that has been locked across Southern Ontario the past week is on the way out. But first that relief will come in the form of a cold front that is likely to clash with the hot air to create some strong thunderstorms ahead of the front.

Some of these storms, particularly in Eastern Ontario during the afternoon on Thursday could reach severe levels with strong wind gusts being the main threat. One or two tornadoes are also possible with the strongest environment being along a corridor from Tweed to Ottawa.

With the cold front already on our doorstep as of early Thursday morning, it is expected to gradually slide across Southwestern Ontario and the Golden Horseshoe through the overnight and pre-dawn hours on Thursday.

While this isn’t ideal timing for storm development, we can’t rule out some nocturnal development. And if these developments occur, the environment could certainly support a few marginally severe storms primarily with strong wind gusts and heavy rainfall.

The tornado risk isn’t zero, but it’s also not particularly strong due to the timing of the overnight storms. But the environment could support a brief spin-up through Southwestern Ontario into the GTA, but it’s very questionable.

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Join us on YouTube as we track any storms that develop throughout the day on Thursday

For Deep Southwestern Ontario, we are looking at the bulk of the risk between midnight and 6am with non-severe storms potentially continuing until 9am. These storms could bring isolated damaging wind gusts, nickel-sized hail and 50-100mm of rain.

In Southwestern Ontario, the risk follows a similar overnight pattern as Deep Southwest, though it’s slightly more delayed. The environment will still support some isolated strong wind gusts and localized flooding, but again, the timing works against widespread severe development. The threat of large hail and a brief tornado is low, but not zero. The risk should ease by the time we hit the late morning hours.

For the Golden Horseshoe, storms are expected to roll through in the mid-to-late morning hours, primarily between 6:00 a.m. and 12:00 p.m. Similar to the regions farther west, the overnight timing limits storm strength, but a few marginally severe cells are possible.

Gusty winds, heavy downpours and nickel-sized hail are the main concerns. The tornado risk is quite low, though not completely off the table. Things should quiet down quickly as we head into the early afternoon

In Central Ontario, storms may get going a bit earlier compared to the GTA, potentially arriving in the pre-dawn hours and continuing through the morning.

The main threat here also leans toward damaging wind gusts and flooding, especially if storms repeatedly track over the same areas. Nickel-sized hail is possible, and while the tornado risk is low, it’s not zero. Timing should help reduce the severity, but there’s still a window for a few stronger cells.

Eastern Ontario is where the severe threat becomes much more notable. As the front progresses into a more unstable environment in the afternoon, the potential for strong storms ramps up.

Damaging wind gusts appear to be the most likely hazard, but one or two tornadoes are also possible, particularly along a corridor from Tweed to Ottawa, where models show the strongest instability and tornado environment overlapping.

Hail around quarter-size and localized flooding are also concerns with any stronger storms that develop.

Southeastern Ontario will also be in the bullseye for strong to severe storms, particularly from late afternoon into the early evening. Kingston through Brockville and into Cornwall sits right along the corridor of stronger wind potential.

Wind gusts may reach damaging levels, with a few storms capable of producing quarter-sized hail. Flooding is also possible in areas that get hit by repeated rounds.

While the tornado risk isn’t as pronounced as the Ottawa Valley, it’s still something we’ll be watching closely.

For our updated map, it’s largely unchanged from our preliminary forecast. The main changes we made was shrinking the ‘widespread’ risk zone to cover Eastern Ontario only. The latest data suggests that the Niagara region is less likely to see storms so the support for a widespread risk is no longer there.

We have also extended the isolated risk into the rest of Southwestern Ontario to cover the very questionable severe risk during the overnight and early morning hours.

For the tornado risk, while there is a non-zero risk for a tornado across all parts of the severe risk, we have focused it on the Ottawa Valley. This is where the latest model data continues to show the strongest tornado risk. Mainly during the mid to late afternoon hours.

There is also a more heightened tornado risk along the London to Hamilton corridor during the morning hours. While the risk isn’t super strong, this is where we believe a tornado is most likely to occur if one does occur in the morning.

The storm risk should taper off around the dinner hour as storms move out into Quebec and Upstate New York.

Heat Wave Ends With a Bang: Widespread Severe Thunderstorm Threat for Southern Ontario on Thursday

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As Southern Ontario continues to deal with a prolonged heat wave, there is some relief on the way. A cold front is expected to sweep through the region on Thursday, bringing temperatures back down to near-seasonal levels. But unfortunately, that relief won’t come quietly.

We’re closely watching Thursday for the potential of severe weather across much of Southern Ontario.

Thunderstorms are expected to fire up along the cold front as it moves through the province, with the potential for widespread severe storms especially across Eastern Ontario, Central Ontario and possibly parts of the Greater Toronto Area (GTA) during the morning and afternoon.

These storms may pack a punch, bringing strong wind gusts, large hail, heavy rain and possibly even an isolated tornado. The best chance for any rotating storms (and tornadoes) will be in Eastern Ontario later in the day when the environment becomes more favourable for storm organization.

With more high-resolution models coming into range, we’re getting a better handle on how things may play out. Based on this data, we’ve put together a preliminary forecast map showing where the greatest risk for severe weather currently appears to be.

That said, this event is still just under 48 hours away, and plenty could still change. The timing, placement and severity of storms may shift, so expect updates over the next couple of days. We’ll be keeping a close eye on the data and will continue to post updates as things evolve.

ESTIMATED TEMPERATURE in °C - MAP FROM WEATHERBELL

At this point, it looks like the cold front will reach the western parts of Southern Ontario sometime during the morning hours. The strongest environment for severe weather will be just ahead of the front. But because of the early timing, the threat for severe storms in Southwestern Ontario and along the Lake Huron shoreline looks more limited.

Still, the setup could be just strong enough to trigger a few marginally severe storms by late morning or early afternoon as activity moves into Central Ontario and the Golden Horseshoe.

SIMULATED RADAR - MAP FROM WEATHERBELL

As the cold front continues eastward into the afternoon, this is when we expect storm activity to really ramp up. With daytime heating providing an extra energy boost, we’re watching the Peterborough to Bancroft corridor around noon, with storms potentially reaching Kingston and the Ottawa Valley by early to mid-afternoon.

Storms are expected to move out of Ontario and cross into New York and Quebec around the dinner hour. However, this is subject to change depending on the timing of the cold front.

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Given the setup, we’ve gone with a ‘widespread’ (level 2 out of 5) severe risk for much of Eastern Ontario. This includes the potential for several severe thunderstorms capable of producing damaging wind gusts, hail and heavy rainfall.

We’ve also extended this risk into parts of the Niagara region where some models are hinting at rapid storm development during the early afternoon before storms cross the border.

The rest of Southern Ontario, excluding Deep Southwestern Ontario and the Lake Huron shoreline, falls under an ‘isolated’ (level 1 out of 5) severe risk. Most storms in these areas will likely stay below severe limits, but a few could briefly become marginally severe during the morning or early afternoon.

Currently, Deep Southwestern Ontario and Northeastern Ontario are not in the risk zone for severe weather on Thursday. That’s due to the early arrival of the cold front which will likely move through these areas before storms have a chance to fully develop. That could change should the cold front arrive later in the day when the environment is strongest.

ESTIMATED Morning LOW in °C - MAP FROM WEATHERBELL

In the wake of the cold front, temperatures will drop significantly Thursday night into Friday morning. Some higher elevation areas in Central Ontario could wake up to morning lows in the upper single digits!

Most of Southern Ontario will see lows in the low to mid teens, which will be a welcome change after several nights of muggy 20°C+ lows.

ESTIMATED DAYTIME HIGH in °C - MAP FROM WEATHERBELL

Daytime highs on Friday will also cool back to near-seasonal values, with most of the region seeing mid-20s. But enjoy it while it lasts. A gradual warm-up is expected over the weekend with temperatures climbing back into the upper 20s and even low 30s by early next week.

Southern Ontario Faces Widespread Severe Threat Including Damaging Wind Gusts, Toonie-Sized Hail & Tornado Risk on Friday

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After Southern Ontario experienced some severe weather last weekend along with our first significant heat wave of the season, things have quieted down over the past few days. Milder air brought temperatures back to seasonal values on Wednesday and Thursday.

However, it looks like we’re about to heat up again heading into the weekend. The good news is, it won’t be anywhere near the oppressive heat we saw earlier this week.

In addition to the return of summer warmth, there’s a growing risk of widespread severe storms on Friday. This threat covers much of Southwestern Ontario and stretches into parts of Central Ontario and the Golden Horseshoe.

Isolated thunderstorms are expected to fire up over Lake Huron and move into a very unstable environment during the afternoon, leading to the possibility of all severe weather hazards. This includes damaging wind gusts, large hail and potentially even one or two tornadoes.

As these storms push eastward into the evening hours, there’s a chance they could merge into one larger cluster of storms. This line may reach portions of the Greater Toronto Area and bring a continued threat of damaging winds, small hail and localized flash flooding.

ESTIMATED DAYTIME HIGH in °C - MAP FROM WEATHERBELL

While the heat has pulled back across much of Southern Ontario over the past few days (except for Deep Southwestern Ontario), we’re expecting it to return on Friday. Areas south of Lake Simcoe will likely see daytime highs climb back into the upper 20s and even low to mid-30s across parts of Southwestern Ontario.

This won’t be the same level of heat we saw earlier in the week, but it will be a noticeable jump compared to the cooler air on Thursday that kept many places under 20°C for most of the day.

Once you factor in the humidity, some parts of Deep Southwestern Ontario could be feeling close to the upper 30s again.

SIMULATED RADAR - MAP FROM WEATHERBELL

As we often see on days with elevated storm risk, the morning could bring some scattered showers or thunderstorms near Lake Huron and Georgian Bay. These are not expected to be severe, but they will play an important role in shaping the setup for later in the day.

If the morning rain and storms linger longer than expected, they could limit afternoon storm development by preventing the atmosphere from fully recovering. This could reduce the strength or delay the timing of any severe storms into the evening when conditions aren’t quite as favourable.

There’s also some disagreement in the forecast models about how far south this morning precipitation might extend, especially in the zone where the severe risk is currently expected to be the highest.

SIMULATED RADAR - MAP FROM WEATHERBELL

If the atmosphere is able to recover in time, we could see isolated storms begin to fire over Lake Huron as early as mid-afternoon (2 to 4 PM), then track inland toward Grey, Bruce and Huron counties.

There’s still some uncertainty on the exact placement of this development. Storms could form anywhere along a corridor stretching from Manitoulin Island all the way down to Sarnia.

ESTIMATED ENVIRONMENT FOR TORNADOES - MAP FROM WEATHERBELL

As these cells develop over Lake Huron, they’ll be moving into a rapidly strengthening environment. Current model data suggests the highest tornado potential may be from Goderich to Owen Sound around 3-5 PM.

This region could see the greatest risk for severe weather during the mid to late afternoon hours. Storms that remain isolated early on may evolve into supercells capable of producing damaging wind gusts, large hail and a tornado or two.

While this particular setup leans more toward Southwestern Ontario, other models point to a similarly strong environment farther northeast into Central Ontario. This includes areas around Lake Simcoe, as well as parts of Simcoe County, Muskoka and the Kawartha Lakes.

SIMULATED RADAR - MAP FROM WEATHERBELL

As the storms push eastward during the late afternoon, current data suggests they may merge into one larger cluster of storms by the time they reach Central Ontario and then move into the Greater Toronto Area during the early evening.

At that point, the tornado threat will decrease, but the risk of damaging winds will become the dominant threat. This is typical when storms evolve into more linear systems.

Flash flooding could also become a major concern, especially in urban areas like the GTA, which are more prone to poor drainage. Some forecast models even suggest that this line could stall or ‘train’ over the same area, which would bring the potential for very heavy rainfall in a short amount of time.

The overall severe threat should begin to wind down between 9 and 10 PM as the sun sets and daytime heating fades. That said, the storm cluster may continue eastward into the Niagara Region and parts of Eastern Ontario overnight, though it’s expected to be non-severe by then.

As mentioned, the highest severe threat will likely be in the mid to late afternoon over Southwestern Ontario, especially as storms come ashore from Lake Huron.

These storms could bring damaging wind gusts, hail up to the size of toonies and possibly one or two tornadoes. The tornado risk would be greatest shortly after the storms reach land and should taper off farther inland.

Deep Southwestern Ontario might also see a few isolated storms develop during the afternoon, though the environment doesn’t look quite as favourable compared to areas farther north.

Still, any storms that do form here could bring isolated damaging wind gusts, quarter-sized hail and even a low-end tornado risk that can’t be ruled out.

As the storms move into Central Ontario later in the day, the primary risk will transition to damaging winds. The threat of hail and tornadoes will decrease, but a few storms could still produce quarter-sized hail and, again, an isolated tornado remains possible.

There’s also the potential for some isolated development around Georgian Bay and Lake Simcoe in the afternoon. If that happens, it could boost the tornado and hail risk across that region.

By the time the line of storms reaches the Golden Horseshoe, it will likely be starting to weaken. However, it could still bring the potential for isolated wind damage, nickel-sized hail and maybe a brief tornado, though that risk becomes increasingly unlikely at that point.

Southern Ontario to Kick Off Summer This Weekend With Significant Severe Risk and Tornado Threat on Saturday; Sizzling Heat Near 40°C on Sunday

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Summer officially arrived late Friday night with the summer solstice, and it looks like Mother Nature isn’t wasting any time making it feel like summer across Southern Ontario. A multi-day heat wave is on the way, bringing the potential for record-breaking temperatures starting Sunday and continuing into early next week.

But before the heat sets in, we’re looking at what could easily be our strongest and most widespread severe weather threat of the season so far on Saturday. There are a lot of factors at play that make this a classic ‘boom or bust’ setup, which we’ll break down below.

There’s high confidence in a potent storm environment stretching across much of Southern Ontario. The big wildcard, however, is whether storms will actually develop to take advantage of all that energy. If they do, they could bring very large hail, destructive wind gusts, and possibly even a couple of tornadoes.

What’s especially concerning is that the storm environment doesn’t fade away after sunset like it typically does. In fact, it remains quite strong through the overnight and into Sunday morning, which could support a nocturnal line of storms with widespread damaging wind potential.

Once the severe risk passes, intense heat begins to build. Temperatures will soar well into the 30s by Sunday, with humidex values making it feel closer to the 40s. The heat continues Monday and Tuesday, with some relief expected midweek. That said, it’ll likely stay warm into the end of June and possibly early July.

A key ingredient in Saturday’s severe weather threat is already unfolding over North Dakota early Saturday morning. An intense line of storms, known as a “derecho” (a fast-moving complex of severe thunderstorms that can produce widespread wind damage), is sweeping through the northern Plains.

This system is producing destructive wind gusts of over 150 km/h along with several tornadoes and has already left damage in its wake. It’s expected to continue tracking eastward into the Great Lakes region through the day.

SIMULATED RADAR - MAP FROM WEATHERBELL

So what does that mean for Southern Ontario?

Derechos are known to travel long distances, and current model guidance suggests this one could follow a path toward Northeastern Ontario. Areas near the U.S. border, including Sault Ste. Marie and Elliot Lake, could be affected by the remnants of this system Sunday morning.

There’s still some uncertainty around how strong the system will be by the time it reaches Ontario. Forecast models often struggle with capturing the evolution and intensity of derechos, so the possibility that this one is being underestimated shouldn’t be ignored.

SIMULATED RADAR - MAP FROM WEATHERBELL

The projected track of what’s left of this potentially decaying derecho places it crossing Lake Huron and Georgian Bay into Central Ontario sometime Saturday afternoon.

If it maintains strength, it could bring damaging wind gusts, hail up to the size of toonies and maybe even an isolated tornado. But this could just be the first of multiple storm rounds.

Some models are also hinting at additional isolated storm development around Elliot Lake and Sudbury in the wake of the earlier line. That suggests the atmosphere could quickly recharge, although it’s still unclear how widespread any new storms would be.

ESTIMATED ENVIRONMENT FOR TORNADOES - MAP FROM WEATHERBELL

As we move into the late afternoon and evening hours on Saturday, the storm environment really ramps up. One of the key indicators we look at, the Significant Tornado Parameter, is literally off the charts in some areas, particularly near the Lake Huron shoreline and into Georgian Bay.

Here’s the catch, though: storms need to develop in this environment to take advantage of it. If they do, they could rapidly become severe, with the potential for all hazards. That includes large hail (possibly golf ball-sized or bigger), destructive winds over 100 km/h, and tornadoes.

SIMULATED RADAR - MAP FROM WEATHERBELL

Looking at what one model is simulating, there’s a notable lack of storms in the highest risk areas around Lake Huron. Instead, storms appear to fire up along a line from Sudbury to Parry Sound through Muskoka, just northeast of the most primed environment. These storms could still be strong and bring similar hazards.

It’s worth noting that models may be underdoing storm development in Southwestern Ontario. That’s something we’ll need to monitor in real time. If nothing happens in Southwestern Ontario, it could end up being a ‘bust’ - which would be good news for those who aren’t fans of severe storms.

ESTIMATED ENVIRONMENT FOR TORNADOES - MAP FROM WEATHERBELL

Typically, severe weather threats wind down after sunset as daytime heating fades. But in this case, models are suggesting the environment will remain unusually supportive of storm activity well into the overnight hours and early Sunday.

There’s even the potential that a new line of storms forms north of Georgian Bay and sweeps southeast through Southern Ontario overnight. If this happens, it could evolve into another derecho-type system - similar to the one seen Friday night in North Dakota.

Forecasting derechos is notoriously difficult, as models often fail to capture their full strength and endurance. While nothing is certain, this setup definitely has the ingredients to support a nocturnal derecho-type event.

If this scenario plays out, we could see widespread wind damage across Central and Eastern Ontario, possibly extending into parts of Southwestern Ontario and the Golden Horseshoe.

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This is a very tricky forecast, and while we've gone with a ‘significant’ (level 4 out of 5) risk, that doesn’t mean everyone will see storms. The risk will come in waves, and some areas may be completely missed.

That said, the potential severity of any storms that do form justifies this level of concern. We’re talking about the possibility of golf ball-sized hail or larger, destructive wind gusts (possibly from a derecho), and a few tornadoes. The tornado risk will largely depend on storm structure—more linear setups will favour damaging wind, while discrete supercells could increase the tornado threat.

The highest severe risk covers areas around Georgian Bay including Sault Ste. Marie, Elliot Lake, Manitoulin Island, Britt, and into Central Ontario such as Muskoka, Simcoe County and Bancroft.

A broader ‘strong’ risk zone includes much of Central and Eastern Ontario, the northern portions of Southwestern Ontario, and the Greater Toronto Area.

Meanwhile, areas like London, Kitchener, Hamilton and the Niagara region fall into the widespread severe risk category.

For once, Deep Southwestern Ontario may dodge the worst of the storms. Windsor, Chatham and Sarnia are currently in the isolated severe risk zone. While a stray storm can’t be ruled out, most of that region looks to stay quiet Saturday.

There may be another round of severe weather on Sunday afternoon and evening, but confidence in the details is still low. Eastern Ontario may be favoured, but we’ll refine that forecast once Saturday plays out.

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Sunday marks the beginning of an extended stretch of dangerously hot temperatures. The most intense heat is expected across Deep Southwestern Ontario into the Golden Horseshoe.

Areas like Windsor, Sarnia, London, Hamilton, Kitchener and Toronto could see daytime highs between 35°C and 40°C. With humidity, it will feel like the mid-40s in many spots.

Locations near Lake Ontario, Lake Erie, Lake Huron and Georgian Bay will be 5 to 10 degrees cooler, but it doesn’t take much distance inland to hit the oppressive heat.

Elsewhere in Southern Ontario, expect highs in the low to mid-30s with humidex values near 40°C.

Heat Safety Tips:

• Stay hydrated and avoid strenuous outdoor activity during peak heat hours.

• Check in on vulnerable individuals, including the elderly, young children and those with health conditions.

• Never leave pets or people in parked vehicles.

• Use fans or air conditioning when possible and find shade or cooling centres if needed.

SOURCE: ECCC

There’s a good chance many locations will break temperature records going as far back as the 1800s over the next few days.

According to Environment Canada, record highs in cities like Toronto, Windsor, Ottawa, London and Hamilton are in the mid to upper 30s for Sunday, Monday and Tuesday. Based on the current forecast, some of these records may fall.

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Monday brings more of the same, with extreme heat expanding into parts of Central and Eastern Ontario in addition to Southwestern Ontario and the GTA.

Once again, humidex values will push into the 40s, making it feel extremely uncomfortable and even dangerous for some.

Tuesday will still be hot, but may be slightly cooler compared to Monday. Some relief is on the way by Wednesday, although temperatures will likely stay warm overall.