Southern Ontario: ‘Snow Day’ Forecast for Wednesday, December 3, 2025

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Snow squall activity off the northeastern shoreline of Georgian Bay has weakened substantially compared to earlier in the day, allowing Environment Canada to drop all of the warnings.

Even so, light lake effect snow is expected to persist through the overnight hours around the Parry Sound area. This could bring an additional 5 to 10 cm of snow by Wednesday morning in the most persistent bands.

Because of the earlier snowfall and the likelihood that rural roads will take some time to be fully cleared, we believe there is still a chance that the Near North District School Board may decide to cancel buses for another day.

Our confidence is not particularly high, so we have capped the probability at 50 percent for the Parry Sound region, 25 percent for East Parry Sound and 10 percent for North Bay.

Elsewhere, we are not expecting any hazardous winter weather conditions that would lead to bus cancellations on Wednesday. So it looks like you should plan to do your homework!

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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 Tuesday, December 2, 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

• Near North Public & Nipissing-Parry Sound CathoIic: Busses are cancelled for the Weather Zones of West Parry Sound, East Parry Sound South, Trout Lake/Four Mile Lake Road, and Redbridge/Thorne today.

French Schools

• Le Conseil scolaire public du Nord-Est de l’Ontario (CSPNE) & Conseil scolaire catholique Franco-Nord: Busses are cancelled for the Weather Zones of West Parry Sound, East Parry Sound South, Trout Lake/Four Mile Lake Road, and Redbridge/Thorne today.

Southern Ontario: ‘Snow Day’ Forecast for Tuesday, December 2, 2025

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/12/2/bus-cancellations

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

Localized, intense snow squalls are expected to persist off the northern and northwestern shoreline of Georgian Bay overnight and into Tuesday morning. Environment Canada has issued snow squall warnings for the Parry Sound region, noting the potential for 20 to 40 cm of snowfall in the most intense bands.

This level of snowfall will very likely lead to bus cancellations in the hardest hit areas, which fall primarily under the Near North District School Board. We have assigned a 90 percent chance for the Parry Sound region, a 75 percent chance for East Parry Sound and a 50 percent chance for North Bay, where the impact from the squalls is expected to be more variable for those further inland.

The Bruce Peninsula, under the Bluewater District School Board, may also be affected by this lake effect activity. However, confidence is lower here, so we have gone with a 50 percent chance. Farther north, the Rainbow District School Board and the Algoma District School Board are assigned a 25 percent chance, with Manitoulin Island being the most likely area to see cancellations. The Greater Sudbury region is much less likely to reach cancellation thresholds.

In addition to the lake effect snow, a separate system is expected to track across the Northeastern United States on Tuesday. Its northern edge may bring periods of light to moderate snowfall to areas along Lake Erie and Lake Ontario, extending into Eastern Ontario during the morning hours. Accumulation will be limited, generally 4 to 8 cm closest to the U.S. border, tapering off to the northwest.

Normally, this level of snowfall would not meet the threshold for cancellations in most school boards. However, because it coincides with the morning commute, we have assigned a 5 percent chance for regions along the Lake Erie shoreline.

For Eastern Ontario, we have given a 10 percent chance to the southern portion of Tri-Board Student Transportation Services. This region tends to be more sensitive to weather conditions, and if Environment Canada were to issue any winter-related advisories, they often cancel based on that guidance. It is still a long shot, but as we saw Monday morning, this area can react quickly to even minor impacts. Other rural school boards in Eastern Ontario have a 5% chance of a snow day.

For the rest of Southern Ontario, we are not expecting any significant snow or hazardous conditions that would lead to cancellations on Tuesday.

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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, December 1, 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

• Near North Public & Nipissing-Parry Sound CathoIic: School Bussing is cancelled in the Weather Zone of Redbridge/Thorne today.

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

• Tri-Board: Due to ongoing snow covered conditions on many secondary & side roads, transportation is cancelled in Tri-Board’s North Lennox & Addington and North & Central Frontenac weather zones today.

French Schools

• Le Conseil scolaire public du Nord-Est de l’Ontario (CSPNE) & Conseil scolaire catholique Franco-Nord: School Bussing is cancelled in the Weather Zone of Redbridge/Thorne today.

Southern Ontario: ‘Snow Day’ Forecast for Monday, December 1, 2025

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/12/1/bus-cancellations

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

The system that brought widespread snowfall to Southern Ontario on Sunday has now begun to move out of the region. In its place, a sharp drop in temperatures has allowed lake effect snow to develop southeast of Lake Huron and Georgian Bay.

This lake effect activity is expected to continue through the overnight hours and into Monday morning. Local snowfall totals may reach up to 15 cm in the most persistent bands. Environment Canada has issued a mix of snow squall watches and warnings for the areas most likely to be affected.

However, there is still quite a bit of uncertainty surrounding the exact intensity of these squalls and how long they will hold together. Because of this, we are not confident that conditions will reach the threshold needed to prompt widespread school bus cancellations. As a result, the highest probability on the map is capped at 50 percent along the southeastern shoreline of Lake Huron, where warnings are currently in effect and the most organized bands are expected to form.

This 50 percent zone includes southern Huron County within the Avon Maitland District School Board. It also extends into Middlesex County under the Thames Valley District School Board. These regions sit closest to the shoreline hotspot and stand the best chance of seeing stronger, more persistent squalls early Monday morning.

Surrounding this area, we have assigned a 25 percent chance for several boards that remain under a snow squall watch or tend to maintain a higher threshold for cancellations. This includes the London region of the Thames Valley District School Board and the west zone of the Simcoe County District School Board. We have also included northern Huron County and southern Perth County under the Avon Maitland District School Board, as well as the Kincardine, Southampton and Meaford regions within the Bluewater District School Board.

Temperatures are expected to fall quickly overnight, which may lead to icy and slick road conditions by the early morning commute. This is especially true in rural areas where backroads often remain snow-covered or untreated. Because of this, we have assigned a very low to low chance across rural portions of Central and Eastern Ontario. While cancellations are not expected, we cannot fully rule out a few isolated decisions if icy conditions become more impactful in rural areas.

Elsewhere across Southern Ontario, the chance of a snow day remains very low.

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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.

Yet More Snow on the Way for Southern Ontario With a Snowy System on Sunday Bringing Up to 10-20cm

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As many communities in the snowbelt regions around Lake Huron and Georgian Bay are currently digging out from locally over 50cm of snow from squalls over the past two days, another snow maker is already on the way, just in time for the final days of November.

Instead of very isolated pockets seeing intense snowfall totals as we have seen with the lake effect activity, this system will spread accumulating snow across almost all of Southern Ontario. Widespread totals by the end of the weekend are expected to range from 5 to 15cm, with locally as much as 20cm in the areas that remain colder for longer.

Snowfall is expected to begin moving in from the west by late Saturday evening, starting first across Deep Southwestern Ontario. By the middle of the overnight, steady light to moderate snowfall will extend across almost all of Southern Ontario as the system further progresses into our region.

By late Sunday morning, southwesterly winds flowing across the still warm waters of Lake Erie and Lake Ontario are expected to push temperatures several degrees above freezing along the northern shorelines. This may allow the last remaining few hours of precipitation to switch over to rain for some communities right along the lakeshore.

There could also be a lake effect component to this system as it departs our region to the east. As this happens later in the day on Sunday, we may see locally heavier pockets of lake effect snow develop east of Lake Huron and Georgian Bay, which also happens to include some of the same areas hit hard by the squalls over the last few days. This could push weekend totals into the 20 to 25cm range, especially if these bands linger longer into Sunday night.

Looking ahead to the start of the week, Monday should be fairly quiet as the lake effect activity tapers off early in the morning and the remaining flurries from the system fizzle out. It will certainly be colder with everyone seeing temperatures plunge below freezing. However, that calm weather may be short-lived.

There are early indications of another potential system sliding south of the Great Lakes region. Depending on the track, this could bring another round of heavy snow throughout the early part of Tuesday, especially for areas further southeast.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

The initial bands of snowfall associated with the weekend system will begin to enter Southwestern Ontario from the west sometime just after the dinner hour on Saturday.

For most areas, the snowfall should be fairly light at first, but some models are showing the potential for several hours of heavier snowfall rates approaching 2 to 4cm per hour for Windsor, Leamington and Chatham. This could lead to a quick 5 to 10cm by the end of the night if the heavier bursts materialize.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

As we head into the overnight hours, the system is expected to continue spreading eastward across Southern Ontario, with almost all areas seeing steady snowfall by the middle of the overnight.

Snowfall rates are not expected to be overly extreme, with most regions seeing less than 1cm per hour through Sunday morning. Even still, this snowfall is expected to continue for 6 to 12 hours, which will allow the totals to gradually build up.

Because the snow will be more widespread and less intense than recent squall activity, road crews should be able to keep up with the conditions on most major routes. Travel delays are still likely, so if you do need to drive, be sure to leave plenty of extra time and adjust your speed based on the conditions.

TEMPERATURE - MAP FROM WEATHERBELL

Winds are expected to pick up through the later part of Sunday morning, coming out of the southwest, and flowing across Lake Erie and Lake Ontario. This will push warmer air into the northern shorelines, which may allow the snow to switch over to rain directly along the Lake Erie and Lake Ontario shorelines.

Due to this transition, slightly lower snowfall totals are expected here, and some areas may struggle to reach the 5cm mark. This includes the Greater Toronto Area near the lakeshore, along with Port Colborne, Norfolk County, Tillsonburg, St. Thomas and Rondeau.

PRECIP TYPE - MAP FROM WEATHERBELL

The system is expected to gradually taper off through Sunday afternoon, leaving scattered flurries in its wake into the evening. This leftover precipitation is likely to be enhanced by Lake Huron and Georgian Bay through Sunday evening and into the overnight hours.

Expect an additional 5 to 10cm of snowfall on top of the system totals in the areas that see lake effect enhancement. This could push the end-of-weekend totals to locally as much as 20 to 25cm in the traditional snowbelt regions.

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When it comes to the distribution of precipitation, we expect it to fall fairly evenly across the province. However, snowfall totals will vary based on temperature differences, which will influence how efficiently the snow can accumulate.

The higher snowfall totals from this event are expected in the more northern sections of Central Ontario and extending into the Sudbury and North Bay region. This includes Parry Sound, Muskoka, Algonquin Park and Bancroft.

These regions will see more sustained below freezing temperatures throughout the event, along with lake effect enhancement late Sunday. With this, we are looking at around 10 to 20cm, with locally up to 25cm possible in the heavier lake effect pockets.

A similar situation is expected east of Lake Huron and along the higher elevations of the Dundalk Highlands and Oak Ridges Moraine, where slightly colder temperatures will help accumulations. Expect 10 to 20cm in these areas as well, with localized totals around 25cm, especially east of Lake Huron.

Everyone else, with the exception of the Lake Erie and Lake Ontario shorelines, is looking at a general 5 to 10cm. Some areas could see locally up to 15cm if temperatures end up just a bit cooler than expected. This includes the rest of Southwestern Ontario into Windsor, Chatham and Sarnia, the Lake Simcoe region and parts of the Ottawa Valley.

For communities exposed to the shorelines of Lake Erie and Lake Ontario, which includes Toronto, Oshawa, Oakville, Hamilton, Niagara-on-the-Lake, Port Colborne and Rondeau, snowfall totals will likely be closer to the 2 to 5cm range due to the warmer air intrusion and rain mixing during the latter part of the system.

PRECIP TYPE - MAP FROM WEATHERBELL

As we look into next week, we are closely watching another potential system that could have an impact on Southern Ontario throughout the day on Tuesday. There is still some uncertainty on the exact track, with the latest model runs shifting it slightly further north, which would increase impacts across a wider portion of the region. However, it could easily shift back south.

At this point, we can say there is a decent chance of 5cm or more across a wide stretch of Southern Ontario, with the highest probability being further southeast, including the Niagara region and communities along the St. Lawrence River. Be prepared for possible impacts to the Tuesday morning commute, including the potential for school bus cancellations if the system trends stronger.

Expect possible impacts to the morning commute on Tuesday, including possible school bus cancellations, should we see a stronger system.

Southern Ontario: School Bus Cancellations and Closures for Friday, November 28, 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

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

• BIuewater Public & Bruce-Grey Catholic: All busses are cancelled.

• Grand Erie Public & Brant HaIdimand Norfolk Catholic: Today, services in all 4 zones are cancelled due to current secondary road conditions and forecasted whiteout conditions during morning run time. As a result, schools are also closed.

• Simcoe County Public & Simcoe Catholic: Busses are cancelled for the North, Central, and South Zones.

• Thames Valley Public & London CathoIic: Busses are cancelled for Oxford County.

• WaterIoo Public & WaterIoo Catholic: All busses are cancelled.

French Schools

• Conseil scolaire catholique Providence: Busses are cancelled in Oxford and Bruce-Grey.

• Conseil scolaire Viamonde: Busses are cancelled in Oxford and Bruce-Grey.

‘Snow Day’ Forecast: Widespread School Bus Cancellations Expected in Southern Ontario’s Snowbelt on Friday

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For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/11/28/bus-cancellations

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

Snow squall activity has been developing off Lake Huron and Georgian Bay throughout the day on Thursday and is only expected to intensify as we head into the overnight and early morning hours of Friday.

These snow squalls are forecast to become nearly stationary, affecting much of Grey and Bruce counties, Huron County, Perth County, Wellington County, Simcoe County and parts of the northern Greater Toronto Area.

With snowfall rates reaching 5 to 10 cm per hour in the heaviest bands, along with strong winds causing blowing snow and localized blizzard conditions, it is almost certain that school buses will be cancelled in the hardest hit regions on Friday. School closures are also possible as we are likely to see numerous road closures overnight, with conditions continuing to worsen.

We are most confident in a snow day for the southern portion of the Bluewater District School Board, along with the entire Avon Maitland District School Board. We have assigned these regions a 90 percent chance of school bus cancellations.

These areas are positioned to face the full impact of the long-lasting snow squalls through Friday morning, making it extremely unlikely that buses will be able to operate safely, especially across rural roads.

Outside of these zones, we also have fairly strong confidence in cancellations along the southeastern shoreline of Georgian Bay. This includes the Simcoe County District School Board (west and central areas), the northern section of the Bluewater District School Board, Wellington County under the Upper Grand District School Board, and the Thames Valley District School Board’s Oxford and Middlesex regions.

While confidence is high, there remains a chance that a few of these regions might attempt to run buses either because they sit just outside the core impact zone or because the school board typically has a higher threshold for cancellations. This is especially true for Simcoe County, which has been particularly strict about cancelling buses this season despite strongly worded warnings from Environment Canada. With all of that in mind, we have assigned these regions a 75 percent chance.

The probability drops off quickly outside the primary snow squall corridor. We have a 50 percent chance for the Simcoe County District School Board’s north and south areas, the Bruce Peninsula, Dufferin County, Waterloo Region under the Waterloo Region District School Board, and the London area under the Thames Valley District School Board.

In these regions, it could go either way and will largely depend on the exact positioning of the squalls. For Kitchener and London specifically, both are more urban school boards with a higher threshold for cancellations.

We have assigned a 25 percent chance for Elgin County under the Thames Valley District School Board, the Grand Erie District School Board, York Region under the York Region District School Board, the northern portion of the Durham District School Board, and the southern section of the Trillium Lakelands District School Board, including the southern City of Kawartha Lakes.

While we do not expect widespread cancellations here, if the squalls push far enough inland and produce pockets of whiteout conditions, there is still room for some surprises.

Elsewhere across Southern Ontario, there is less than a 25 percent chance of a snow day.

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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.

BIG CHANGES Coming to Environment Canada’s Alerts Beginning Today

Environment Canada is making big changes to the way it issues weather alerts, in an attempt to make them easier to understand at a glance.

Starting today, Wednesday, November 26th, 2025, the new system will use Yellow, Orange or Red colours for all 'Advisories', 'Watches' and 'Warnings'.

'Statements' will remain unchanged (blue or grey), for now.

Environment Canada is making this change to hopefully help you quickly gauge both the severity of a weather event and the level of confidence forecasters have in their predictions.

Shown in the chart above, Environment Canada forecasters will choose the colour of alerts based on an "Impact" level and a "Confidence" level.

Here’s a breakdown of the upcoming changes and what they mean for you.

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Headline Changes

Currently, weather alert headlines look like this:

Heat Warning

Under the new system, the headline will include a colour code that signals risk. For example:

Yellow Level Warning – Heat

We at Instant Weather feel that something about "Yellow Level Warning – Heat Issued" looks… strange and extra confusing.

Therefore, when we post Environment Canada alerts to social media, send notifications via our free app, and send out text message alerts, we're going to format it like this:

Heat Warning (Yellow Level) Issued

We believe this will make the transition from the old format to the new format easier for our community members. However, we'd love to hear your feedback on this so please let us know what you think about it!

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NEW COLOURS

For the first time, advisories, watches and warnings will come in one of three colour options:

- Yellow = low risk (stay alert)

- Orange = moderate risk (take precautions)

- Red = high risk (serious danger)

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Impact Level

The new Impact Level will estimate how much damage or disruption a storm is likely to cause.

Possible values:

- Low

- Moderate

- High

- Extreme

For example, a minor snowfall could be flagged as low impact, while a hurricane might carry an extreme impact designation.

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Confidence Level

The new Confidence Level should help clarify how confident the Environment Canada forecaster issuing the alert feels.

Possible values:

- Low

- Moderate

- High

- Very High

For example, a “very high confidence” alert means there's near zero question if the storm poses a threat to the alerted area, while a “low confidence” could suggest that path may shift direction or the storm could dissipate.

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Why These Changes Matter

Environment Canada believes these updates make weather alerts more actionable and accessible. Instead of vague warnings, you’ll know:

- The severity of the threat (colour level).

- The expected damage (impact level).

- The certainty of the forecast (confidence level).

For further details on these alert changes, visit Environment Canada’s newly launched website regarding colour-coded alerts:

https://www.canada.ca/en/services/environment/weather/severeweather/weather-alerts/colour-coded-alerts.html

Southern Ontario: School Bus Cancellations and Closures for Thursday, November 27, 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

• 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 busses are cancelled.

• 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 due to road conditions

• Near North Public & Nipissing-Parry Sound CathoIic: All School busses in West Parry Sound ( Britt/Nobel - Mcdougall/Whitestone/Ahmic Harbour - Town of Parry Sound - Mactier/Humphrey/Rosseau) are cancelled for today

• Upper Grand Public & Wellington CathoIic: All school taxis and buses in Centre Wellington, The Town of Erin and the Town of Rockwood (Division 2), North Wellington (Division 3), and Dufferin County as well as to Robert F. Hall Secondary School (Division 4) will not be operating today. Schools in North Wellington (Division 3) are CLOSED.

French Schools

‘Snow Day’ Forecast: Intense Snow Squall Risk Could Cancel School Buses in Parts of Southern Ontario on Thursday

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/11/27/bus-cancellations

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

Snow squalls are expected to affect areas around Lake Huron and Georgian Bay throughout the day on Thursday. Environment Canada has issued widespread snow squall watches and warnings for the regions most likely to see hazardous conditions.

This setup raises the chances of school bus cancellations, although there is still some uncertainty because the most intense activity is expected later in the day. This puts school boards in a position where they may need to make proactive decisions early Thursday morning.

The highest chances for cancellations are in Southern Grey Bruce and Northern Huron and Perth Counties. Environment Canada has issued a strongly worded snow squall warning for these zones, highlighting the risk of very low visibility and rapid snow accumulation. Because of this, we have assigned these regions a 75 percent chance of a snow day.

Near North, which includes Parry Sound, also sits at 75 percent. This is not necessarily due to extreme snowfall expectations, but rather because that school board has historically been more sensitive to weather disruptions.

Other areas closer to the snowbelt, including TLDSB, Simcoe, Northern Grey Bruce, Dufferin, Wellington and Kitchener-Waterloo, fall into the 25 to 50 percent range. Conditions here remain somewhat variable and will depend on how the bands set up through the morning. While we are leaning toward buses running in most of these regions, there is still a decent chance that a few boards will make the proactive call to cancel.

For the rest of Southern Ontario, the chance of cancellations stays below 25 percent. Limited impacts are expected outside the traditional snowbelt, so we do not anticipate widespread issues in these areas.

Looking ahead, the chances of a snow day increase significantly on Friday. A more intense round of snow squalls is expected to develop overnight Thursday into Friday morning, bringing the strongest activity of the week right when buses would be on the roads. You can expect the next update in our snow day forecast to show much higher probabilities and quite a bit more red and pink across the map.

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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.

Dangerous Snow Squalls Target Southern Ontario’s Snowbelt Starting Thursday With Up to 75cm of Snow Possible

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Confidence continues to grow in what is shaping up to be a potentially dangerous snow squall event for regions east of Lake Huron and southeast of Georgian Bay as we wrap up the week.

Temperatures are expected to drop sharply overnight Wednesday, which will help kick the lake effect snow machine into gear as early as Thursday morning.

At first, the activity should be fairly limited. Scattered pockets of lake effect snow are expected to develop east of Lake Huron and Georgian Bay as a westerly wind pattern holds through the morning. Impacts will be minor at this stage, but this early activity will set the stage for a much more intense setup later in the day.

Rapid changes are expected by late Thursday morning and especially into the afternoon. This is when more organized squalls will begin to form.

The worst conditions are expected to develop late Thursday and last into Friday morning. A brisk northwesterly wind will allow narrow but powerful bands of snow to strengthen off both Lake Huron and Georgian Bay. These bands will be capable of producing snowfall rates near 5 to 10 cm per hour at times, along with near-zero visibility.

Travel will likely become extremely difficult through the hardest hit regions. Strong winds will create blowing snow and possibly even brief blizzard conditions. Road closures are possible, and anyone with non-essential travel plans should consider postponing. School bus cancellations appear likely for Friday, and there is even some potential for cancellations on Thursday, depending on how quickly conditions deteriorate.

The main snow squall activity is expected to taper off throughout the day on Friday, although some scattered bands could linger into Saturday. By the end of the day Friday, some areas east of Lake Huron, such as Goderich, Kincardine and Stratford, may be digging out from more than 40 cm of snow. Other parts of the snowbelt may see anywhere from 10 to 40 cm, depending on how close they are to the core of the activity.

PRECIP TYPE - MAP FROM WEATHERBELL

As mentioned earlier, Thursday morning will start with some light to moderate activity east of Lake Huron and Georgian Bay. This includes Grey Bruce, Parry Sound and Muskoka.

Impacts should be limited at first since the snow will be fairly light, but Environment Canada currently has a snow squall watch in effect for this entire region due to what will likely unfold later in the day.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

Conditions will escalate quickly heading into the late morning and afternoon as scattered flurries begin organizing into more defined bands. We expect a fairly long squall to develop over Lake Huron, cross the Bruce Peninsula and come onshore east of Georgian Bay. This could bring a few hours of heavy snow to the Muskoka region.

Additional pockets of lake effect snow may also fire up further south off Lake Huron, affecting areas like Goderich, Hanover, Stratford and Kitchener.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

That Georgian Bay squall is expected to gradually sink southward as the wind shifts from westerly to northwesterly. This will cause a swath of intense snow to drift across the Highway 11 and 400 corridor between Bracebridge and MacTier, down toward Barrie.

A few hours of rapid whiteout conditions are possible during the afternoon. Even though temperatures may hover near the freezing mark, which slows accumulation, visibility will still be extremely poor and blowing snow will create dangerous travel conditions.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

Conditions will worsen significantly into the evening as the squall drifts far enough south to draw its full moisture supply from Lake Huron instead of Georgian Bay. This new orientation will allow the band to tap into a longer stretch of open water, which increases its intensity.

At this point, several intense bands could stretch inland between Kincardine and Goderich and reach as far east as Kitchener and even the western GTA at times.

There is still some uncertainty in how these bands will align. A slight shift in wind direction can cause a squall to lock in place further north or drift south. This will dramatically affect who sees the heaviest snow. Regardless, conditions will be poor even in areas that are not directly underneath a streamer due to the blowing snow.

Within the core of the squalls, snowfall rates of 5 to 10 cm per hour will be possible. Thundersnow and lightning cannot be ruled out, given the strength of the setup.

Georgian Bay will see a brief lull with lighter pockets of snow affecting the South Muskoka to Simcoe County corridor. This break will be short-lived as winds shift yet again heading into the overnight hours.

Hourly snowfall rates (cm) - MAP FROM WEATHERBELL

The most dangerous conditions are likely overnight Thursday into Friday morning. A very intense squall off Lake Huron is expected to set up somewhere between Goderich and Kincardine and stretch inland toward regions between Kitchener and London.

There is still uncertainty about the exact placement. Even a tiny shift in wind direction could pin this band farther north or push it farther south. At times, it may also extend into Hamilton and the Niagara region with quick bursts of heavy snow and whiteouts.

Southeast of Georgian Bay, more organized bands are likely to develop from Barrie into Kawartha Lakes. Some of this activity may also clip the northern GTA, including York and Durham. The Georgian Bay squall will likely be weaker than the Lake Huron band, but model trends have strengthened it slightly in the latest data. Peak snowfall rates will likely sit around 3 to 6 cm per hour in the strongest areas.

Temperatures will plunge well below freezing overnight which will help snow accumulate far more efficiently.

Most model data suggests that the lake effect bands will remain locked in place through Friday morning, although the intensity may gradually decrease during the afternoon as winds begin to ease. Snow squalls could continue into Saturday, but confidence drops for the weekend pattern since the bands may become more fragmented and less organized.

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As always with lake effect snow, exact totals are extremely difficult to predict. These events can produce huge differences over very short distances. One community could pick up 50 cm while another, only a few kilometres away, sees barely any accumulation.

Even with this uncertainty, the most consistent model signal points toward a high-impact zone east of Lake Huron, picking up a general 40 to 75 cm of snow by Friday evening. This includes Goderich, Point Clark, Kincardine, Mildmay, Wingham, Clinton, Mitchell, Listowel and Stratford.

Localized totals near 100 cm cannot be ruled out, although these would be isolated pockets rather than widespread amounts.

A wider zone east of Lake Huron that stretches into the Kitchener area has the potential to see 20 to 40 cm of snowfall accumulation.

For Georgian Bay, the squall should be weaker than the Lake Huron band. We are going with 20 to 40 cm for regions like Collingwood, Wasaga Beach, Midland, Orillia, Barrie, Innisfil, Angus and Keswick. This may end up being a slight overestimate if the squall fails to organize as we saw in the last event, which significantly underperformed.

Muskoka, Parry Sound, Kawartha Lakes and parts of the eastern GTA may see 10 to 20 cm depending on how far the bands push inland.

Less than 10 cm is expected for the rest of Southern Ontario, including Eastern Ontario, the Golden Horseshoe and deep Southwestern Ontario, since they will be far enough removed from the main lake effect activity.

Winter Storm Targets Northern Ontario This Week as Intense Snow Squalls Line Up for Southern Ontario Starting Thursday

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A powerful system will sweep through the Great Lakes region this week, bringing a major winter storm to Northern Ontario and setting the stage for a significant snow squall event across Southern Ontario later in the week.

Across Northern Ontario, snowfall will begin to move into regions east of Lake Superior by late Tuesday. Light snow will start from Wawa through Timmins, gradually expanding north and west. Through the overnight hours into Wednesday morning, the system will push into Thunder Bay, Kapuskasing and surrounding communities.

The worst conditions are expected throughout the day on Wednesday. Winds will gust between 40 and 60 km/h, and when combined with heavy snowfall rates, visibility will deteriorate quickly. Blowing snow will be widespread across Northeastern Ontario and conditions may even reach blizzard levels at times.

Treacherous travel conditions will continue into Wednesday night and persist through Thursday morning as the storm deepens. Snowfall intensity will gradually ease later on Thursday, but steady snow will continue as the system stalls over Quebec. This will push long lasting bands of precipitation back into Northeastern Ontario, keeping snow going until early Friday morning.

By the time the storm fully exits, a wide swath of Northeastern Ontario is expected to receive 20 to 50 cm of snow, with localized totals possibly exceeding that. The heaviest totals are expected from Marathon through Kapuskasing, Cochrane, Timmins, and Temiskaming Shores, Wawa, Hearst and Chapleau. Snowfall totals here will range from 30 to 50cm with possibly as much as 60cm in localized pockets.

While Northern Ontario deals with the winter storm, Southern Ontario will be on the warm side of the system on Tuesday and Wednesday. Many areas will flirt with the double digits, especially in Southwestern Ontario. Scattered showers will develop early Tuesday with light rainfall amounts of roughly 5 to 10 mm.

By late Wednesday, though, the pattern begins to shift as cold air wraps in behind the departing system. Temperatures will drop quickly, and any lingering precipitation will change to wet snow by Wednesday evening.

This colder air will set the stage for lake effect snow to fire up. With a westerly wind overnight on Wednesday, snow squalls may begin to develop off Lake Huron and Georgian Bay.

These early bands could bring bursts of heavy snow to Grey Bruce, Parry Sound and Muskoka through Thursday afternoon, although the exact intensity remains uncertain as the higher resolution models are just entering range and showing stronger signals than the medium range guidance.

By late Thursday, winds will shift to a northwest flow. Temperatures will drop further into the negatives and this will allow squalls to strengthen. The Georgian Bay band is expected to sink south into Simcoe County and then extend into Kawartha Lakes and Peterborough.

At the same time, the Lake Huron band will slide south into Huron County and stretch toward Kitchener and the western GTA. Some early guidance even hints that this band could link up with the flow off Lake Superior, which can enhance snowfall rates.

Heading into Friday, it is still too early to give precise band placement. Current thinking suggests the northwest flow will hold through much of the day before winds start easing over the weekend. If that happens, squalls could remain active for an extended period.

While details can still shift, we are beginning to narrow down regions with the highest risk of heavy snowfall starting Thursday morning and continuing into Friday evening. Squalls will shift around at times, so snowfall will not be constant, but those under the core of the bands could see snowfall rates approaching 5 to 10 cm per hour. It will not take long for the snow to accumulate.

At this stage, exact totals are not possible to predict for Southern Ontario. However, some regions could easily see 25 to 50 cm by Friday night, with the potential for higher localized totals once high-resolution data comes into range.

For Lake Huron, our current focus areas include Kincardine, Goderich, Hanover, Kitchener, Hamilton and Orangeville.

For Georgian Bay, our primary targets include Midland, Barrie, Gravenhurst, Bracebridge, Orillia, Kawartha Lakes and Peterborough.

Anyone living in or near these regions should be prepared for dangerous travel conditions beginning Thursday. School bus cancellations are likely for some regions, and road closures are possible if squalls remain intense or stationary.

Widespread 5–15cm of Fresh Snow to Blanket the Southern Prairies Early This Week

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As we get closer to the start of the storm expected to cross the Prairies and weather models have come closer in agreement, we now have more confidence to discuss the potential impacts over the next couple of days. This storm will travel eastward along the international border, which will limit most of the snowfall to southern portions of all three Prairie provinces.

Alberta

The snow will make its way into Southwestern Alberta after midnight, gradually spreading eastward across the province during the early and mid-morning hours. It’s during this time that there is also a risk of freezing rain for communities closer to the border, but it will quickly be replaced by snow. Meanwhile the scattered flurries remaining from Sunday through Calgary to Red Deer are also expected to organize and intensify, joining the snow further to the south.

The rdps model showing precipitation type and intensity at 7am MT on Monday, courtesy of WeatherBell.

As we get later in the morning, there will likely be some intensification and increased snowfall rates along the Highway 3 corridor and southward, which will result in greater overall accumulation. By lunchtime, the snow will begin to taper off to the north of Calgary and then from west to east starting in the early afternoon and exiting the province completely in the evening.

A widespread 5-15cm of snow is predicted by the end of Monday across Southern Alberta and areas that experience the heavier snowfall closer to the border could be on the higher end of that range. There could be pockets where accumulation totals could approach 20cm to the south of Highway 3, but this is much more likely to occur east of Highway 36.

The rdps model showing precipitation type and intensity at 7pm CT on Monday, courtesy of WeatherBell.

Saskatchewan

The leading edge of the snow will move into Southwest Saskatchewan in the mid-morning and it will spread eastward across the province through the day. There is also the slight risk for some freezing rain along the border to the south of Maple Creek and Shaunavon, but it should be over quickly.

The snowfall across Saskatchewan will be fairly short-lived and by the time the snow reaches the Manitoba border in the evening, it will actually start to taper off back along the Alberta border. Throughout the remainder of the evening, overnight and into Tuesday morning, the snow will gradually end from west to east.

Similarly to in Alberta, much of Southern Saskatchewan can expect at least 5cm of snow by midday Tuesday. There will also be heavier snowfall from Maple Creek to Estevan, mostly along Highway 13 and southward. This particular region will likely see snowfall totals around 20cm and Environment Canada may issue a snowfall warning to reflect this.

The rdps model showing precipitation type and intensity at 7am CT on Monday, courtesy of WeatherBell.

Manitoba

By the time the snow makes its way into Manitoba Monday evening, the entire system is expected to shift course and start moving more in a southeast direction as it interacts with another low pressure system from the States. As a result, the steady moderate snowfall will not extend as far east through the province. Regardless, the snow will still make its way across Southern Manitoba overnight and into Tuesday morning. It will slowly start to taper off from west to east around sunrise, gradually ending for border communities in the Eastman Region Tuesday evening.

The system will also start to weaken as it makes its way into Manitoba, so the heavier snowfall expected in both Alberta and Saskatchewan is looking like it won’t be as much of a concern. There will still be a swath of the region that can expect more than 5cm of snow by the end of Tuesday, but it is likely that this won’t exceed 10cm.

It is possible that this change in direction is more subtle than showing on weather models or doesn’t occur at all. We will watch as the system takes shape and makes its way through Alberta and Saskatchewan. If it appears that the track will change from what was initially expected, it’s likely that we will update our forecast for Manitoba.

As it stands, a decent amount of snow is expected to fall across the Southern Prairies. This snow will be heavy in some areas, which will likely make travel a headache, especially on some of the busier highways. Be sure to give yourself plenty of extra time if travelling during these periods of heavy snowfall and stay safe.

Southern Ontario: School Bus Cancellations and Closures for Friday, November 21, 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

• Near North Public & Nipissing-Parry Sound CathoIic: There are several routes cancelled due to inclement weather. For a full list, visit :https://geoquery.npssts.ca/Alerts

• Tri-Board: Due to freezing rain received overnight, transportation is cancelled in Tri-Board’s North Hastings and North Lennox & Addington weather zones today.

French Schools

Rare November Stratospheric Warming Event Could Spread Arctic Chill Across Canada for December

You may have heard a new term being thrown around in the news and on social media: “Sudden Stratospheric Warming”. It’s not a new term, meteorologically speaking, and it’s related to the polar vortex. It happens most winters, but it’s making headlines now because of how early it is happening; it has only occurred three times in the month of November over the last 70 years. Additionally, this could be the earliest instance of sudden stratospheric warming on record and it could lead to some very cold temperatures across the country in the coming weeks.

It’s certainly nothing we can’t handle, but it’s always interesting to learn about how something happening in the Arctic, 10s of kilometres above the surface, can impact our day-to-day weather.

Before we dive into what sudden stratospheric warming is, however, we’re going to need a bit of background information. The first thing we need to know is what and where the stratosphere is.

The layers of the atmosphere. Image courtesy of NOAA.

The Earth’s atmosphere is made up of layers and the stratosphere is the second layer from the surface, stretching from 10-50km above the surface. It sits on top of the troposphere, which is where we live and all our weather occurs. The two layers are separated by the tropopause, where the temperature stops decreasing with height and it instead stabilizes. Moving higher, into the stratosphere, the temperature increases with height and the layer itself is quite stable, making it ideal for commercial planes to fly in.

Next, we need a bit of understanding of the polar vortex. This is a concept that has become more mainstream in the last 10 years or so, but there’s a bit more to it than just a period of cold weather.

The easiest way to explain the polar vortex is to imagine a spinning wall of wind, called the polar night jet, in the stratosphere that traps cold air over the Arctic. The polar vortex is always there, but it is weaker in the summer and stronger in the winter during polar night, which is how the polar night jet gets its name.

A stable polar vortex vs a disrupted polar vortex. Image courtesy of NOAA.

When the polar vortex is stable, it can be almost perfectly circular and centred over the North Pole, while the polar jet stream in the troposphere stays further north and flows west to east. However, the polar vortex can be disrupted and the circulation weakened, allowing cold air to flood southwards and pushing the polar jet stream further south and making it become wavy.

One of the main ways the polar vortex can be disrupted is through a sudden stratospheric warming event. As the name suggests, sudden stratospheric warming is when we see sudden warming in the stratosphere, particularly over the polar regions. This could be upwards of 40°C of warming over the course of only a few days!

Sudden stratospheric warming is typically caused by strong upper level high pressure that interacts with the low pressure polar vortex. The high pressure pushes the polar vortex away from the North Pole, settles there in its place and blocks out the polar vortex. Air always falls within a high so once the high pressure replaces the polar vortex, the air in the stratosphere collapses, warming as it falls due to compressional heating and resulting in the sudden stratospheric warming.

Meanwhile, the polar vortex has become weakened and disrupted, forcing the polar jet stream to become wavy and the polar night jet slows down or even reverses direction. This all results in cold air flooding the mid-latitudes throughout the Northern Hemisphere until the blocking high weakens and the polar vortex can restrengthen, allowing it to move back to over the North Pole.

The modelled presence of a high over the north pole (shown in Yellow, red and Pink)and the polar vortex at lower lower latitudes (shown in blue, purple in green) on November 23rd. image courtesy of WeatherBell.

Weather models are showing that we could see the beginnings of a sudden stratospheric warming event starting in the coming days and temperatures in the stratosphere could jump to 30°c above normal. This means that there could be an outbreak of cold Arctic air in the next two weeks or so.

How long this cold air outbreak lasts is dependent on the strength of the sudden stratospheric warming event. If the incoming high pressure is disruptive enough for the winds of the polar night jet to reverse, the Arctic air could persist over the country for several weeks. Two of the previous three instances of sudden stratospheric warming in November saw this wind reversal and in those years, the cold lasted throughout the month of December.

The GFS Model of temperature anomalies (departures from normal) on the morning of November 30th. Image courtesy of WeatherBell.

It’s important to note that there is still some uncertainty in how all of the pieces will come together for this possible sudden stratospheric warming event and there’s a slight possibility that it doesn’t even happen. However, it’s becoming increasingly likely that we will see a disruption in the polar vortex so it becomes a question of who gets the cold, how cold it gets, and for how long.

The American GFS model, for instance, shows the Arctic air arriving in British Columbia and Alberta by mid-next week and spreading eastward in the following days. By Sunday morning, much of the country could see temperatures well below seasonal and some areas could see temperatures of 20°C below normal.

As we get closer to the sudden stratospheric warming taking place, we will have a clearer look at how long the Arctic air could be around. Until then, now might be a good time to dig out all your winter gear because you might need it!

Southern Ontario: School Bus Cancellations and Closures for Monday, November 17, 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

French Schools

‘Snow Day’ Forecast: Possible Bus Cancellations in Southern Ontario’s Snowbelt With Squalls Continuing Into Monday

For an updated list of school bus cancellations & school closures, please visit our live article: https://instantweatherinc.com/article/2025/11/17/bus-cancellations

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We’ve seen snow squalls developing off the southeastern shorelines of Lake Huron and Georgian Bay as of Sunday evening. These squalls are expected to continue through the night, and there is a good chance they will intensify as colder air pours in.

Accumulation from these squalls could reach 30 to 40cm in the hardest hit areas. With Environment Canada issuing snow squall warnings for several regions, it’s looking very likely that school buses will be kept off the roads on Monday, where conditions are at their worst.

The highest level of certainty for a snow day is southeast of Lake Huron. This is where the most intense squall activity is expected to set up and persist overnight. That includes the Exeter region of AMDSB and the Middlesex area of TVDSB. We’ve given both zones a 90 percent chance of a snow day on Monday based on the current setup.

Elsewhere in AMDSB and TVDSB, the chance of bus cancellations ranges from 50 to 75 percent. The closer a region is to the heart of the snow squalls, the higher the likelihood of cancellations. Farther out, confidence drops as it becomes less clear how far inland the heavier bands will reach.

We’ve also assigned a 50 percent chance to the Kincardine and Southampton regions under BWDSB. A weather advisory is currently in place there, but confidence is lower compared to areas southeast of Lake Huron. The snowfall might still fall short of what boards in that area need to see before pulling the plug on buses.

For the Georgian Bay snow squall, the highest risk sits in Simcoe’s west zone, including Collingwood. This area sits closest to the lake and is in the best position to see the most intense and consistent snowfall overnight. Simcoe’s Central and South zones, as well as Dufferin County, are sitting at a 50 percent chance. The main challenge here is determining whether the squall will stay strong enough as it pushes inland and exactly where that band decides to park itself.

York Region has been given a 25 percent chance, mainly for its northern sections, where some of the Georgian Bay activity could drift in. However, York tends to be more urban, and school boards in these areas are usually more cautious with cancellations, which lowers the confidence.

Much of the rest of Southern Ontario is sitting at a less than 10 percent chance of a snow day on Monday. These regions are simply too far from the lake effect zones to be significantly impacted by the squalls.

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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.

Snow Squalls Take Aim at London, Barrie and Northern GTA on Sunday With Up to 25-50cm of Snow Possible

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We enjoyed a brief break from the wintry weather on Saturday as temperatures soared into the double digits across much of Southern Ontario. The exception was Eastern Ontario, where the Ottawa Valley dealt with hours of freezing rain.

But that warm spell is going to be short-lived. Cooler air returns overnight into Sunday, and temperatures will slide back below the freezing mark. Once that happens, the lake effect snow machine will fire up again for the next couple of days.

And no, it isn’t déjà vu. The target zone for this round of squalls will look very similar to last week’s event, but the focus shifts slightly east. That puts areas like London, Barrie and even the Northern GTA, including York Region, in line to be hit hard.

By the time the squalls wind down on Monday, the hardest hit spots could be digging out from more than 25cm, with the potential for very localized pockets of 50cm.

PRECIP TYPE - MAP FROM WEATHERBELL

We expect the snow squall activity to begin ramping up late Sunday morning. As temperatures fall, lake effect rain bands will flip over to snow off the southeast shoreline of Lake Huron and Georgian Bay.

While the changeover happens in the morning, ground temperatures may stay just above freezing for several hours. This means the first few hours of snow could melt on contact. Accumulation will start later in the day once temperatures reach the freezing mark.

Even before the snow begins to stick, visibility will drop quickly. Those in the affected areas should expect sudden whiteouts and dangerous driving conditions.

Hourly snowfall rate (cm) - MAP FROM WEATHERBELL

By the dinner hour, the squalls will become much more organized. Snowfall rates from the Lake Huron band could rise to 5cm per hour. This main band is expected to extend from Lake Huron through Goderich and southern Huron County into the London region.

Additional squall activity will form southeast of Georgian Bay, running from the shoreline through Barrie and Angus and into Newmarket and Durham. This band looks weaker than the Lake Huron squall at first, but could still deliver rates of 2 to 4cm per hour.

Hourly snowfall rate (cm) - MAP FROM WEATHERBELL

The worst conditions are likely around midnight. The Lake Huron band is expected to lock onto London, bringing intense snow and rapid accumulation of 6 to 8cm per hour.

The Georgian Bay squall will also strengthen, sliding south of Barrie and focusing on Angus, Bradford and Newmarket. Some signals show it reaching into the Eastern GTA, including Scarborough, Ajax and Oshawa.

These squalls should remain mostly stationary overnight, although minor drifting is possible. As temperatures fall several degrees below freezing, expect snow to pile up quickly.

Hourly snowfall rate (cm) - MAP FROM WEATHERBELL

By mid-morning Monday, the bands will begin to weaken as winds shift more westerly. Some lake effect flurries could linger east of Lake Huron into Grey Bruce, but they are not expected to be very organized. Everything should taper off by late Monday.

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Snow squall forecasting always comes with big caveats. The bands are extremely narrow, which means the difference between 50cm and almost nothing can be only a few dozen kilometres.

This is why we provide a broad range. They help capture that uncertainty, but they are not a guarantee. With this event, the bands appear very intense but also very narrow, which means gradients will be sharp.

Based on the latest data, we expect the hardest hit areas from the Lake Huron squall to include Goderich, Clinton, Lucan, Exeter, Mitchell and London. Snowfall totals here could range from 25 to 50cm, with the chance that someone ends up over 50cm in a very localized spot.

Surrounding regions, including Grand Bend, Tillsonburg, Stratford, Wingham, and Point Clark, could see 15 to 25cm.

Further east into Grey Bruce and Dufferin County, we are expecting 5 to 15cm mainly on Monday as the lake effect shifts northward.

The Georgian Bay band looks even narrower than the Lake Huron band. A small corridor stretching from Collingwood through Angus and into Innisfil could see 25 to 35cm, with a chance of 50cm if the band really intensifies.

The City of Barrie is right on the edge. A small shift north or south would bring very different results. For now, the highest totals look likely in the south end of the city with 15 to 30cm. The north end may be closer to 10 to 20cm.

Substantial totals may also extend into the Northern GTA, including Bradford, Newmarket and Aurora. Totals along the Highway 400 and 404 corridor could range from 15 to 30cm.

Across the east end of Toronto and Durham, including Ajax, Pickering and Oshawa, occasional heavy bursts may bring 5 to 10cm.

The rest of Southern Ontario should see less than 5cm of snow by Monday from the lake effect.

All the Seasons in One Weekend for Southern Ontario as Freezing Rain, Thunderstorms and Snow Squalls Line Up

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There is really only one way to describe what November has been like across Southern Ontario when it comes to the weather: a roller coaster.

Last weekend brought our first widespread snowfall event of the season. That was quickly followed by intense snow squalls that buried parts of the Lake Huron shoreline with more than 50 cm of snow early this week.

That seasonal whiplash continues this weekend as a clear battle sets up between cold, wintery air and much milder fall-like conditions. Eastern Ontario, especially around the Ottawa Valley, will stay on the cold side with a risk of prolonged freezing rain throughout the day on Saturday.

Southwestern Ontario and the Golden Horseshoe will see a completely different story. Temperatures are set to rise into the double digits, and there is even a risk of thunderstorms on Saturday. Some of the warmest pockets around Windsor could briefly flirt with the 20s for a few hours.

By late Saturday, a sharp cold front will sweep through the region. This will send temperatures plunging again heading into Sunday, settling the battle in favour of the colder air. As this cold push arrives, the lake effect snow machine is expected to roar back to life over both Georgian Bay and Lake Huron.

TEMPERATURE - MAP FROM WEATHERBELL

We expect a frosty start to Saturday morning for most of Southern Ontario. Deep Southwestern Ontario will be the main exception as milder air starts to slide in early. Most areas should wake up close to the freezing mark. Deep Southwestern Ontario will already be climbing through the mid single digits.

By noon, Deep Southwestern Ontario should reach the double digits. Further northeast into the rest of Southwestern Ontario, the Golden Horseshoe and parts of Central Ontario, temperatures will range from the low to mid single digits. The Ottawa Valley will remain near the freezing mark well into the afternoon as the surge of mild air stalls just to the southwest.

PRECIP TYPE - MAP FROM WEATHERBELL

A developing system will start to spread heavy precipitation into Southern Ontario late Saturday morning or early afternoon. For most areas, temperatures will be warm enough for rain to be the dominant precipitation type. There’s even the risk of a thunderstorm!

Over the Ottawa Valley, however, we expect patchy freezing rain to form as temperatures linger stubbornly near the freezing mark.

Model guidance is not fully aligned on how warm the air will get in that region. Even a small shift of one or two degrees will change how long the freezing rain lasts and how much ice is able to accrete. This is one of the key uncertainties for Saturday.

TEMPERATURE - MAP FROM WEATHERBELL

Through Saturday evening, temperatures will continue climbing across much of Southwestern Ontario. Cities like London, Kitchener and Hamilton are expected to reach the double digits.

One important note is that daytime highs in many areas will actually be reached late in the evening instead of during the normal warmest part of the day!

Meanwhile, that pocket of near-freezing air over the Ottawa Valley is expected to hold on into the evening, which could allow several more hours of freezing rain.

As the system pulls east overnight Saturday, colder air will sweep in behind it. Temperatures will tumble through Sunday morning, switching any lingering precipitation to wet flurries by the time you wake up.

Hourly snowfall rate (cm) - MAP FROM WEATHERBELL

Behind the front, bands of lake effect snow will begin developing off Lake Huron and Georgian Bay early Sunday. These bands look messy and disorganized through much of the day, although localized totals of 10 to 20 cm are possible.

By late Sunday, more focused and intense squalls could form, especially around the London region off Lake Huron. These squalls may continue into Monday and could lead to localized 20+ cm totals.

We will have a more detailed, dedicated lake effect forecast released soon.

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When it comes to freezing rain accretion, there are several variables that could reduce or increase the amount of ice that actually builds up. This is a very temperature-sensitive event.

The heaviest icing is expected directly along the Quebec border and into the Hawkesbury region. Models show the potential for over 10 mm of freezing rain, but it is unclear how much of that will be able to stick. Heavy precipitation rates could limit the amount of ice that accumulates, and temperatures will sit very close to the freezing mark for much of the event.

Given all of this, we are going with a general 5 to 10 mm of icing for the hardest hit areas. If temperatures are even slightly warmer than expected, accretion could end up lower. This is certainly enough to lead to localized power outages and icy roads.

For the City of Ottawa, they sit right on the dividing line between lighter icing and heavy icing. We have placed them in the 2 to 5 mm range, but they could see locally up to 7 mm if the cold air becomes more stubborn than currently forecast.

Outside of the Ottawa Valley, expect minimal icing. Areas such as Bancroft, Cloyne, Perth, Carleton Place and Cornwall may see an hour or two of freezing rain before changing over to rain.