Severe Thunderstorm & Isolated Tornado Threat on Tuesday for Southern Ontario

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After experiencing a chilly start to April, Southern Ontario is finally feeling the warmth, bringing a more spring-like atmosphere to the region. This warmth will be especially noticeable on Tuesday as temperatures are expected to climb into the upper teens or even low 20s in some areas.

This warming, combined with an approaching cold front later on Tuesday, will set the stage for the development of thunderstorms.

A potent environment conducive to thunderstorm development is expected to materialize across Southwestern and Central Ontario during the afternoon, fueled by ample daylight heating from the warmer temperatures.

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As the cold front sweeps through the province starting in the late afternoon, a line of storms is anticipated to form, extending from North Bay towards Georgian Bay and into regions east of Lake Huron. According to the latest model data, these storms have the potential to become severe, with all types of severe thunderstorm threats being possible.

A slight severe thunderstorm risk extends from Kitchener through Orangeville and Simcoe County into Central Ontario, with a particular emphasis on the corridor from Orangeville to Bracebridge, where models indicate the most conducive environment for severe storm development. The primary window for these storms is between 3 to 8 PM, varying with the arrival time of the cold front.

These storms could bring large hail, up to the size of quarters or ping pong balls, wind gusts of up to 100 km/h, and the possibility of an isolated tornado cannot be ruled out.

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Areas within the isolated severe risk zone might experience a few storms, but the confidence is lower compared to those within the slight severe zone. As the evening progresses, the risk will evolve into a wind threat as the storms merge into a main squall line, advancing towards the Golden Horseshoe and Eastern Ontario.

In Eastern Ontario, non-severe thunderstorms are anticipated around midnight as the weakening line of storms moves through. Although the severe weather risk is expected to be low by the time the storms arrive, small hail and strong wind gusts are still possibilities.

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For Northeastern Ontario, an isolated severe storm threat is forecasted near the North Bay area as storms develop off Georgian Bay. The severity of the storms is expected to lessen further north, with non-severe thunderstorms predicted for the majority of Northeastern Ontario.

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UPDATE: Clouds May Move Out Just in Time for the Solar Eclipse on Monday in Parts of Southern Ontario at the Expense of Eastern Ontario

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We are on the eve of the total solar eclipse set to dim the skies across Southern Ontario on Monday. With the event about 24 hours away, our confidence in the viewing conditions within our region is sharpening. Clear skies are crucial for those looking to fully experience the eclipse, a phenomenon eagerly awaited by many for years.

The experience of a total solar eclipse differs significantly under clear versus cloudy skies. Clear conditions allow observers to witness the dramatic dimming of daylight, a noticeable drop in temperature, and the visibility of stars and planets.

The eclipse's most breathtaking moment, the emergence of the sun's corona, is visible only during totality, revealing delicate, radiant strands extending from the moon's silhouette, an image no camera or telescope capturing partial phases can replicate.

Under cloudy conditions, while some cooling and dimming effects may still be perceptible, the visual spectacle is significantly diminished. Clouds mask the corona, stars, and planets, greatly reducing the visual impact of the eclipse.

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SAFETY WARNING

To safely enjoy the eclipse, it's imperative to use ISO 12312-2 certified solar glasses. Directly observing the sun, even during an eclipse, can cause serious damage to your eyes. You can only view the eclipse without the glasses during the few minutes of totality. Solar glasses are designed to block harmful solar radiation and protect your eyes while allowing you to safely witness the event.

Never use makeshift viewing solutions like sunglasses or homemade filters, as they do not offer adequate protection against the sun's rays. Also, remember that the same rules apply to taking pictures with your phone. The sun can damage your camera’s sensors if you don’t have the proper solar filter (such as the same solar glasses for your eyes).

your guide to the eclipse:

Our initial forecast pointed to the possibility of clouds moving into Southern and Northern Ontario from late Sunday into Monday morning. This outlook holds, according to the latest models, albeit with slight adjustments in the anticipated locations of the densest cloud cover.

A key change concerns Eastern Ontario, where the front edge of the cloud cover is now forecasted to arrive several hours earlier than previously thought. Consequently, areas such as Kingston, Belleville, and Brockville might experience increasing cloudiness before the eclipse begins, potentially obscuring views of the later stages, including totality around 3 PM.

In the Ottawa Valley, cloud coverage remains a possibility, though a very narrow strip of Extreme Eastern Ontario, around Cornwall, is expected to maintain clear skies for the majority of the eclipse. While high-level clouds may still be present, they shouldn't hinder eclipse viewing, as the sun's light should penetrate through.

This shift in cloud movement toward the east spells good news for those in Deep Southwestern Ontario. We now have increased confidence that locations southwest of London, including Sarnia, Chatham, Leamington, and Windsor, will enjoy mostly clear skies at the eclipse's peak.

Even parts of Southwestern Ontario, extending from the southwestern shore of Lake Huron to the Kitchener/Waterloo region, might see clouds dissipate in time for the eclipse.

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The outlook for the Golden Horseshoe, including the Greater Toronto Area and Niagara region, is more uncertain. Clouds are expected to obscure the early stages of the eclipse in the afternoon, but recent high-resolution models suggest possible breaks in the cloud cover around 3 PM, coinciding with the eclipse's maximum.

There's hope that this trend towards earlier cloud clearance continues, potentially offering clear views over the Niagara region right in time for totality. While not guaranteed, the possibility remains, so keep your fingers crossed.

In contrast, Central Ontario and the Georgian Bay shoreline are expected to be under thick clouds during the eclipse, likely obstructing views. Those in these areas hoping to witness the eclipse may need to consider travelling to clearer locations.

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In Northern Ontario, prospects for viewing the partial solar eclipse are less favourable, with extensive cloud cover predicted from Georgian Bay to the Lake Superior shoreline.

Locations such as Elliot Lake, Sault Ste. Marie, Wawa, and Marathon are unlikely to have a clear view of the eclipse. Cloud coverage in Northeastern Ontario is expected to be mostly dense, though it may become more scattered further north.

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As we look at Northwestern Ontario, the viewing conditions are quite poor, especially around the Lake Superior shoreline including Thunder Bay, Kenora and the Armstrong region. Thick clouds will likely make the eclipse hard to view.

Clouds Threaten to Spoil the Solar Eclipse on Monday in Parts of Ontario but Not for Everyone

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CLICK HERE FOR THE UPDATED FORECAST

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The countdown is on for the total solar eclipse set to darken the skies across Southern Ontario on Monday. As the big day approaches, we're gaining a clearer understanding of the expected weather conditions during the eclipse. Clear skies are essential for experiencing the full marvel of the eclipse, an event eagerly anticipated by many for years.

Experiencing a total solar eclipse varies dramatically under clear versus cloudy skies. Clear skies allow you to witness the significant dimming of daylight, a noticeable drop in temperature, and the emergence of stars and planets.

The eclipse's crowning moment, the visibility of the sun's corona, occurs exclusively during totality. This presents the corona's delicate, luminous strands extending from the moon's silhouette in a spectacle unmatched by any camera or telescope viewing partial phases.

However, under cloudy skies, though you may still observe a cooling and dimming effect, the visual wonder is significantly obscured. Clouds conceal the corona, stars, and planets, greatly diminishing the eclipse's visual splendour.

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SAFETY WARNING

To safely enjoy the eclipse, it's imperative to use ISO 12312-2 certified solar glasses. Directly observing the sun, even during an eclipse, can cause serious damage to your eyes. You can only view the eclipse without the glasses during the few minutes of totality. Solar glasses are designed to block harmful solar radiation and protect your eyes while allowing you to safely witness the event.

Never use makeshift viewing solutions like sunglasses or homemade filters, as they do not offer adequate protection against the sun's rays. Also, remember that the same rules apply to taking pictures with your phone. The sun can damage your camera’s sensors if you don’t have the proper solar filter (such as the same solar glasses for your eyes).

your guide to the eclipse:

The weather forecast offers a mix of optimism and caution. Some areas in the path of totality in Southern Ontario might face cloudy conditions, potentially obscuring the eclipse. Yet, certain regions in Eastern Ontario and along the Lake Erie shoreline are expected to enjoy clear skies, offering an unobstructed view of the eclipse.

The latest models predict clouds moving in from the southwest late Sunday, leading to overcast conditions in much of Southwestern, Central Ontario, and the Golden Horseshoe by Monday morning. These clouds are expected to spread eastward throughout the morning and early afternoon, with discrepancies among models regarding the extent and timing of the cloud cover.

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By early afternoon, clearing is anticipated in Deep Southwestern Ontario, just in time for the eclipse's start around 2 PM. In contrast, from Niagara Falls through the GTA to Central Ontario, clouds are likely to persist, though intermittent breaks might still offer glimpses of the eclipse.

Eastern Ontario faces a race against time, with increasing cloudiness expected. The northeastern tip, including Cornwall, may remain clear until later in the afternoon, offering potentially favourable conditions for eclipse viewing. Kingston and Belleville should be mostly clear to start, but again, clouds will increase in coverage during the eclipse so hopefully it can hold off until after totality occurs.

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In Northern Ontario, prospects for viewing the partial solar eclipse are less favourable, with extensive cloud cover predicted from Georgian Bay to the Lake Superior shoreline.

Locations such as Elliot Lake, Sault Ste. Marie, Wawa, and Marathon are unlikely to have a clear view of the eclipse. Cloud coverage in Northeastern Ontario is expected to be mostly dense, though it may become more scattered further north and east.

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As we look at Northwestern Ontario, the viewing conditions are quite poor especially around the Lake Superior shoreline including Thunder Bay and into the Armstrong region. Thick clouds will likely make the eclipse hard to view. There is some chance that those closer to the Manitoba border may see some breaks in the clouds, but it’s unlikely.

‘Snow Day’ Forecast: April Snowstorm Likely to Lead to School Bus Cancellations in Eastern & Central Ontario on Thursday

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A complex weather system has been impacting both Southern and Northern Ontario throughout Wednesday. As the day progressed, temperatures across the region have steadily decreased, leading to the transition of heavy rain into heavy, wet snow by the afternoon and evening.

This snowfall is anticipated to persist into the overnight hours and early Thursday morning. The most significant accumulations are expected across Eastern Ontario, stretching towards the Ottawa Valley, where snowfall totals may surpass 20cm.

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As the snow continues into the night, temperatures will further decline below the freezing point. This will cause any earlier rain and melted snow to freeze, resulting in icy road conditions by Thursday morning. Such conditions are likely to necessitate school bus cancellations across a broad area of Eastern Ontario.

Areas most prone to experiencing a ‘snow day’ on Thursday encompass rural school boards in the Ottawa Valley, spanning northern Tri-Board and extending into Northeastern Ontario, including North Bay and Sudbury. These regions are sitting at a 90% chance of school bus cancellations.

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Surrounding areas, like the central parts of Tri-Board and Parry Sound, have a 75% chance of cancellations. Further south, the probability evens out for regions such as Peterborough, Kawartha Lakes, and Muskoka. Although it’s uncertain how much snow these areas will receive, the potential for icy road conditions might lead to cancellations.

For regions north and west of the GTA, including Simcoe and Dufferin County, there exists a minor possibility of school bus cancellations, though the likelihood remains low. The rest of Southern Ontario has a less than 10% chance of experiencing a snow day.

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.

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Winter Storm Threat Looms for Ontario With Up to 30cm of Snow and 60mm of Rain by Thursday

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The beginning of April in Ontario is setting the stage for a dramatic shift in weather, as a moisture-laden system promises a variety of conditions across the region. This shift includes the potential for flooding rains, with predictions of 40 to 60mm of rain in parts of the Golden Horseshoe.

In addition, areas of Central, Eastern, and Northern Ontario are on track for significant snowfall, with totals ranging from 20 to 35cm in the most affected areas!

As outlined in our previous forecasts, this bout of active weather kicked off with strong wind gusts on Tuesday afternoon, expected to persist into the night.

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With the wind gradually subsiding, our attention now shifts to the substantial moisture being pumped into our region from the Gulf of Mexico. Initially, this precipitation will begin as heavy rain, with intense downpours expected overnight and into Wednesday morning across the Greater Toronto Area, extending into Central and Eastern Ontario.

However, by late Wednesday, colder air from the northwest will sweep in, prompting a gradual transition from rain to wet snow by the late afternoon in parts of Central and Eastern Ontario. Northeastern Ontario, already under colder air by the morning, may experience snow for the duration of this event.

The challenge in forecasting this system lies in the temperatures hovering near the freezing point, significantly impacting snow accumulation. Additionally, model predictions vary on the timing of the transition from rain to snow, some suggesting it won't occur until late Wednesday evening, while others indicate it will occur around 2 to 5 PM.

By Wednesday night, most regions, including the Golden Horseshoe, are expected to have transitioned to wet snow, with light to moderate snowfall persisting into Thursday morning and afternoon, concluding by Thursday evening.

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Elevation will be a crucial determinant of snowfall totals, with the highest accumulations forecasted southwest of Ottawa in Eastern Ontario's elevated areas. This includes Bancroft, Barry’s Bay, Algonquin Park, and Renfrew, with expected snowfall totals ranging from 20 to 35cm by Thursday's end.

For the Ottawa Valley, including Ottawa, Cornwall, Brockville, and Pembroke, snowfall totals are more uncertain, ranging from 10 to 25cm. This variability will depend on local dynamics and the ability of snow to stick to the ground. There is the potential that some areas will exceed our forecast if the snow can stick more efficiently to the ground.

Further south and westward, snowfall totals are expected to range from 5 to 15cm, including Kingston, Peterborough, Huntsville, and Sundridge. Local areas north of the Greater Toronto Area, particularly along the higher elevations of the Oak Ridges Moraine and Dundalk Highlands, may also see up to 10 to 15cm. This forecast is heavily dependent on temperatures, which may not drop below freezing until Thursday morning, affecting accumulation.

Areas east of Georgian Bay and away from Lake Ontario's shoreline are likely to exceed 5cm but should remain under 10cm. Regions directly along the Lake Ontario shoreline and parts of Southwestern Ontario will experience less than 5cm of snow, as rain will dominate these areas.

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In addition to significant snowfall in Central and Eastern Ontario, significant rainfall is anticipated along Lake Ontario's shoreline, including Prince Edward County, Oshawa, Toronto, Mississauga, Burlington, Hamilton, and Grimsby, with potential totals ranging from 40 to 60mm. This rapid accumulation, especially in urban areas prone to flash flooding, poses a substantial flooding risk.

Rainfall totals for the rest of the Golden Horseshoe, extending to the Dundalk Highlands and the Bruce Peninsula, are projected to range from between 30 to 50mm. Further north and east, where more snow is expected to mix in, rainfall totals of 20 to 40mm are likely.

Southwestern Ontario is expected to see lower rainfall totals of 10 to 30mm, with Deep Southwestern Ontario receiving less than 15mm.

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In Northern Ontario, heavy snow is the main concern, with the highest totals just north of Sudbury, anticipating 20 to 35cm of snow from Wednesday morning through Thursday afternoon.

For Sudbury and North Bay, snowfall predictions range from 10 to 25cm. Lower amounts are expected towards Georgian Bay due to rain mixing in, while totals will decrease sharply further north and west due to limited moisture.

Damaging Wind Storm Possible for Parts of Ontario Late Tuesday With 90+ KM/H Gusts

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March may have gone out like a lamb, but the beginning of April is roaring like a lion across Southern Ontario. This is thanks to a strong low-pressure system expected to track across the region. The system will bring a mix of weather conditions from severe winds and rain to the possibility of substantial snowfall as we advance into Wednesday and Thursday.

The immediate concern, however, arises from strong wind gusts anticipated to strengthen by Tuesday afternoon or evening and persisting into Wednesday morning. High-resolution models suggest that some of these gusts could reach damaging levels, surpassing 90km/h in Southwestern, Central, and Northeastern Ontario.

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The initial wave of moisture linked to this system has begun in Deep Southwestern Ontario by Monday evening. Although most of this moisture is expected to remain south of the border, areas along the Lake Erie shoreline could see heavy rain through the early hours of Tuesday. Rainfall totals of 10-20mm are forecasted, with localized areas around Windsor potentially receiving up to 30mm by Tuesday afternoon.

Following this system's departure towards New England, a second system will make its way into the Lower Great Lakes, rapidly intensifying upon its approach. This swift strengthening is expected to generate powerful wind gusts stretching from Michigan into Southern Ontario by Tuesday evening.

Additionally, there's a notable severe thunderstorm risk south of Lake Erie including Ohio and Pennsylvania for Tuesday evening. It looks like the cool waters of Lake Erie will shield Southwestern Ontario from the brunt of the severe weather.

Nonetheless, we cannot entirely discount the chance of an isolated storm making its way into our area. Should this occur, it could bring the threat of large hail and strong wind gusts. While a tornado remains highly improbable, it is not entirely off the table if a storm does cross over.

We will keep a close eye on this development and may issue a thunderstorm forecast should our confidence grow.

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Wind gusts are expected to gradually intensify through Tuesday afternoon, peaking late in the evening or shortly after midnight. Model predictions vary on the peak strength of these gusts, with the Canadian model being somewhat conservative, suggesting gusts may not surpass 80 km/h. Conversely, other models agree on the likelihood of damaging wind gusts exceeding 90 km/h, possibly nearing 100 km/h in some locales.

The areas most susceptible to the strongest wind gusts are to the east of Lake Huron, where gusts could reach between 100 to 115 km/h, affecting Goderich, Kincardine, Hanover, Owen Sound, and Wiarton.

Southwestern Ontario, extending to the Greater Toronto Area (GTA) and the Georgian Bay shoreline, might see wind gusts nearing 90 km/h, though variances are expected, and this represents a potential worst-case scenario. Some locations may fall short of the 90 km/h threshold.

In other parts of Southern Ontario, wind gusts ranging from 70 to 85 km/h are anticipated, with Eastern Ontario likely experiencing a lesser impact.

Power outages are a possibility in regions most affected, so it's wise to prepare for potential extended disruptions, particularly as the wind will accompany heavy rain overnight.

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In Northeastern Ontario, the strongest winds, possibly exceeding 100 km/h, will occur directly east of Lake Superior, including areas like Wawa and Sault Ste. Marie.

Gusts near 90 km/h are forecasted along the northern Georgian Bay shoreline, including Elliot Lake and Sudbury. The rest of Northern Ontario will generally see gusts below 85 km/h, with impacts diminishing further north and west.

The wind threat should subside by Wednesday morning in Southern Ontario but may linger into the early afternoon in Northeastern Ontario.

Following this wind event, attention shifts to the low-pressure system, which will stall over Michigan and draw in moisture from the Gulf of Mexico. This will funnel a significant volume of moisture into Southern Ontario through Wednesday and Thursday.

As colder air envelops Southern Ontario by late Wednesday, a transition from heavy rain to snow is anticipated, particularly in Northeastern, Central, and Eastern Ontario, potentially starting as early as late Wednesday afternoon. Some areas could see over 30cm of snow before it eases off late Thursday.

With the specifics of this transition and the extent of snow accumulation still uncertain, we are waiting to release our detailed forecast for rain and snow until Tuesday. What remains clear is that we are in for a deluge of precipitation over the coming days, with projections of 50-75 mm for certain parts of Southern Ontario. Flooding is a concern, regardless of whether the precipitation falls as rain or snow.

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Potential Snowy Start to April With Up to 20cm in Parts of Southern Ontario Starting Tuesday

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April Fools' Day might be on Monday, but the first week of April is shaping up to be no laughing matter in terms of weather for Southern Ontario. Starting Monday, the lower Great Lakes region is expected to be impacted by a series of systems throughout the week.

The initial two systems are projected to track south of the border, impacting Ohio and Pennsylvania primarily. There's a risk of severe weather on Monday and Tuesday, with a possibility it could extend into Deep Southwestern Ontario. However, the cold waters of Lake Erie should keep most of the severe risk south of the border. We will be monitoring and will have a forecast if it becomes more certain to have an impact on our region.

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These systems are set to bring heavy rain across the Lake Erie shoreline, from Sarnia to the Niagara Region and southward, with some areas potentially receiving 10-20mm of rain from Sunday night into Tuesday morning.

By late Tuesday, a third system is expected to sweep across Southern Ontario, bringing heavy rain throughout Tuesday afternoon and evening for most regions. Temperatures are set to drop from the low to mid-single digits to around or slightly below the freezing mark, causing the rain to transition to snow overnight into Wednesday morning.

The extent of this changeover, however, remains uncertain. Areas near the Lake Ontario shoreline and Deep Southwestern Ontario are likely to remain warm enough to prevent significant snow accumulation. In contrast, Central and Eastern Ontario, along with the higher elevations of the Dundalk Highlands northwest of the GTA, may experience sustained snowfall.

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This snow is expected to persist into Wednesday, with moderate to heavy snowfall continuing into the evening. Strong wind gusts may also contribute to blowing snow and reduced visibility in some areas. Light snow may linger into Thursday for Central and Eastern Ontario, but it won’t lead to much accumulation.

This forecast is preliminary and subject to changes as the system's path and temperatures near the freezing point could significantly affect overall snowfall accumulation.

As of now, Central and Eastern Ontario, including the Ottawa Valley and Muskoka, are anticipated to see 10-20cm of snow. The higher elevations of Algonquin Park and the Ottawa Valley are expected to be closer to the 20cm mark, with Ottawa and Muskoka likely receiving 10-15cm.

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The Dundalk Highlands area could see heavier snowfall, with Orangeville and Shelburne potentially receiving the most, possibly up to 10-20cm. However, this forecast is less certain due to temperature variations that may prevent freezing and cause some melting.

The rest of Central Ontario and the northern part of the GTA could receive 5 to 10cm by Thursday, with the possibility of higher totals if temperatures drop further than currently expected.

Areas near Lake Ontario's shoreline, the Niagara region, and the Lake Erie shoreline are expected to see less snow, with less than 5cm of accumulation. However, significant rainfall poses a concern for these areas, with potential localized flooding due to upwards of 50mm of rain.

We will continue to monitor the latest data and provide a more detailed forecast shortly. Remember, this forecast is very preliminary and could change significantly by Tuesday.

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Niagara Region Declares State of Emergency Ahead of Total Solar Eclipse

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The Niagara Region has officially declared a State of Emergency in anticipation of the large number of visitors expected to arrive for the total solar eclipse on April 8th, which is being hailed as one of the premier viewing opportunities in Canada. In preparation for the arrival of thousands of eclipse enthusiasts, Regional Chair Jim Bradley made the announcement on March 28th, invoking the Emergency Management and Civil Protection Act (EMCPA).

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This step is taken as a precaution to ensure the safety and well-being of both the residents and the visitors coming to witness this unique celestial phenomenon. Local governments, emergency services, schools, and various organizations are working in unison, coordinating efforts with the Province and key partners to ensure a memorable yet safe eclipse viewing experience.

The declaration is set to bolster the region's capabilities in handling large crowds, maintaining essential infrastructure, and responding promptly to any emergencies that might occur. Officials are highlighting the need for preparedness among those planning to view the eclipse, advising adherence to safety guidelines such as the use of ISO 12312-2 certified eclipse glasses and avoiding makeshift viewing methods that can endanger eye health.

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To mitigate the impact of expected large crowds and potential delays, residents and visitors are encouraged to prepare in advance. Recommendations include filling up vehicles with gas, shopping for groceries, and completing errands well before eclipse day to avoid unnecessary congestion. Safe travel practices on April 8th are also emphasized, with advisories against stopping or getting out of vehicles on highways to watch the eclipse.

Given the significance of the event, most schools in the Niagara region will be closed, prompting parents to make alternate childcare arrangements and to educate their children on how to safely observe the eclipse.

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Biggest Snowfall of the Season Possible in Parts of Southern Ontario Including Toronto on Friday With Up to 10-20cm of Snow

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Spring may have officially started earlier this week, but the weather across Southern Ontario has been anything but spring-like. We've experienced lake-effect snow over the last few days, along with temperatures near or below the freezing mark. This marks a significant change from the pattern observed throughout the winter, especially towards the end of winter in February and early March, which saw unusually mild conditions.

Now in late March, we're tracking a potential system that could bring the most significant snowfall accumulation of the season for some regions. While this might sound daunting, it's important to remember that some areas have yet to record even 10cm of snow in a single day this season, so the bar for the 'snowiest day of the season' title is relatively low.

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This system, starting Friday morning and continuing through the day into early Saturday morning, could result in widespread snowfall totals between 10 to 15cm, with possible accumulations reaching up to 20cm. This swath of heavy snow is expected to stretch from the Lake Huron shoreline through the Golden Horseshoe and into parts of Eastern Ontario along the St. Lawrence River.

The initial bands of snow are expected to move into Southwestern Ontario from Michigan during the late morning hours on Friday, spreading eastwards throughout the early afternoon. By late afternoon, the snow will cover much of the Lake Huron shoreline and extend towards the Greater Toronto Area (GTA), ranging from light to moderately heavy snowfall.

There remains some uncertainty regarding the system's track, with some models predicting the heaviest snow band stretching from Kincardine to around Lake Simcoe, while others suggest a more southern route from Grand Bend through Kitchener and into Toronto. The consensus among the models leans towards the southerly track, which we are adopting for now, but adjustments may be necessary if there are shifts in the track closer to the event.

Lake enhancement could also increase snowfall rates off the southwesterly shoreline of Lake Ontario from Toronto to Hamilton on Friday evening, extending overnight into Saturday morning. Another band of heavy snow is expected to move into the Golden Horseshoe, particularly focusing on the Niagara region just before midnight, which is when the highest snowfall rates are anticipated.

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Additionally, there's a potential risk for freezing rain and mixed precipitation along the Lake Erie shoreline and in parts of Deep Southwestern Ontario, including Windsor and Chatham. Currently, the threat of freezing rain seems minimal, but it could change, with some models suggesting more prolonged icing along the shoreline.

The system will progress into Eastern Ontario just after dinner on Friday, with the heaviest snow expected to concentrate along the Hwy 401 corridor from Belleville to Cornwall, persisting into the early hours of Saturday with the most challenging conditions occurring overnight.

Snowfall is expected to taper off from west to east, concluding in Eastern Ontario by early Saturday afternoon.

Based on the current data, snowfall totals are anticipated to range from 10 to 15cm in the hardest-hit regions, including Goderich, Kitchener, Guelph, Hamilton, Toronto, Niagara Falls, Kingston, Brockville, and Cornwall.

Certain areas within this zone could see up to 20cm due to lake enhancement off Lake Ontario, hence the forecast range of 10 to 20cm on our map. If confidence in lake enhancement increases with later model runs, we may need to adjust the forecast up to 15-25cm for parts of the Western GTA.

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DATA and chart FROM WEATHERSTATS.CA

With Toronto expected to receive at least 10cm of snow, this event has the potential to be the snowiest day of the winter thus far, which is quite surprising given that it's already late March. The highest daily snowfall total recorded at Toronto Pearson Airport this winter was 6.4cm on February 15th.

Although Southern Ontario has seen several snowmakers this winter, especially in the snowbelt, the Toronto area has largely been spared, with temperatures along the Lake Ontario shoreline quickly transitioning any snow to mixed precipitation.

We do not anticipate mixed precipitation being a factor for the Toronto area with this system, as temperatures are expected to remain below the freezing mark throughout the event.

Lower snowfall totals are expected to the north, with the Barrie, Orillia, Peterborough, Bancroft, and Ottawa areas likely to see between 5 to 10cm of snow. The same is true for Southwestern Ontario, from Sarnia to London, where totals are unlikely to exceed 10cm.

Less than 5cm of snow is expected in northern Central Ontario, including Muskoka, due to the moisture from the system dropping off and along the Lake Erie shoreline, where mixed precipitation could result in lower snowfall totals.

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

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REGIONS NOT SHOWN ON THE MAP HAVE LESS THAN A 5% CHANCE OF BUS CANCELLATIONS

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Intense snow squalls have developed east of Lake Huron and southeast of Georgian Bay as of Wednesday evening, resulting in significant snowfall accumulation and reduced visibility in the impacted areas. By Thursday afternoon, there is potential for up to 30cm of snow.

Given the expected substantial accumulation and limited visibility continuing into Thursday morning, school bus cancellations are likely.

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The Northern Huron County and Kincardine region, where the worst conditions are anticipated, almost certainly will experience a snow day, with a 90% chance. Surrounding areas, including Perth, Wellington, Grey, Bruce, and Middlesex counties, face a probability of a snow day ranging from 50 to 75%.

Along the Georgian Bay shoreline, Simcoe County's West weather zone has the highest likelihood of a snow day with a 75% chance, while the Central and South weather zones have a 50% chance. Further inland, including London, Kitchener, and York Region, the likelihood of a snow day decreases to a range of 10 to 25%, but it cannot be entirely discounted.

The rest of Southern Ontario has a less than 10% chance of experiencing a snow day on Thursday.

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.

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Lake Effect Snow Targets Parts of Southern Ontario With Over 20cm of Snow Possible by Thursday

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Environment Canada has issued widespread snow squall warnings around Lake Huron and Georgian Bay today. The warning was issued because of the current frontal squall sweeping through the region, coupled with additional lake-effect snow expected to develop later today, persisting into Thursday morning.

Our forecasts often highlight the variability of snowfall totals during snow squall events due to the narrow bands involved. It's not uncommon for one area of a town to experience significant snowfall while an area just 5-10 minutes away receives barely any snow.

Predicting the precise location of these snow bands is challenging as even a slight shift in wind direction can significantly impact the outcome. Typically, we can provide a general idea of which regions will be most affected.

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However, this occasion is different, and we will not be producing our standard polygon forecast map. The three main high-resolution models we rely on for lake effect snow forecasts, HRRR & NAM from the United States and Canada's HRDPS. These models are showing significantly different outcomes, making it impossible for us to offer a forecast with confidence. We believe it wouldn't be responsible to predict something we're not sure about.

Instead, we're sharing the raw model data from these three models, allowing you to see the range of potential scenarios for your location and prepare accordingly. It's important to remember that model data often overestimates actual snowfall, so the amounts shown are likely too high. However, this data is useful for understanding where each model predicts the heaviest snowfall will occur.

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The models mainly diverge regarding the Georgian Bay squall expected to develop this evening and continue into Thursday morning. This squall is predicted to come ashore between Wasaga Beach and Collingwood, extending inland towards Barrie and possibly reaching the northern York Region.

The HRRR model estimates the most snow from this squall, suggesting over 50cm in areas just southwest of Barrie, including Wasaga Beach, Angus, and Alliston.

Keep in mind, that this is just raw model data, and the estimated 50cm is probably an overestimation, especially since the HRRR model tends to overpredict lake effect snow events. Nevertheless, if the HRRR model is accurate, this region could see 20-40cm of snow by Thursday.

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On the other hand, the NAM and HRDPS models predict a much weaker squall off Georgian Bay, with snow totals more in the range of 5-10cm (locally 15cm), and the NAM showing barely a few centimetres. This illustrates the wide variety of potential outcomes, from a few centimetres to over 20cm of snow.

Regarding the Lake Huron shoreline, there is slightly more consensus on overall accumulation, with all three models predicting over 20cm of snow between Hanover and London. However, this prediction still represents a very narrow band, meaning not everyone will see significant snow, and some may see only a few flakes.

Southern Grey and Bruce counties, along with Huron and Perth counties, are expected to bear the brunt of the heaviest snowfall, with totals ranging from 10-20cm and localized pockets possibly receiving 25-30cm. This includes areas like Kincardine, Goderich, Hanover, Listowel, Wingham, and Stratford. The Kitchener and Guelph region may also experience bursts of heavy lake-effect snow, with accumulations ranging from 5 to 10cm.

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Further south, all models concur on another band of lake effect snow southeast of Lake Huron, stretching from Grand Bend to the London area. This band is not expected to be as prolonged or intense as those further north, so snowfall totals will be more in the range of 5 to 10cm by Thursday afternoon.

As the lake effect snow winds down by Thursday's end, our focus shifts to a system arriving late Friday into Saturday that could bring significant snowfall to parts of Southern Ontario. There's some disagreement on the exact path of the system, and temperatures will hover near the freezing mark, potentially leading to mixed precipitation in some areas, affecting overall snowfall totals.

At this stage, a widespread snowfall of 10-20cm, with local amounts up to 25cm, seems fairly likely in parts of Southwestern Ontario and possibly extending into the Golden Horseshoe. We will issue a preliminary forecast soon, so stay tuned for updates!

Ontario to Welcome the First Day of Astronomical Spring With Up to 15-25cm of Snow Between Tuesday & Wednesday

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As we close the chapter on winter with what seemed like an early spring, Ontario is being reminded that winter isn’t going out without a bang. The first day of astronomical of spring arrives on Tuesday, March 19, 2024, at 11:06 PM EDT, but it certainly won’t look like it…

Despite a month filled with unseasonably warm temperatures that saw many regions experience their first 20°C days of the year—quite unusual for this early in the season—the final hours of winter won’t let us forget the season isn’t finished just yet!

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A weak system is set to track across Northern and Southern Ontario from Tuesday morning and persist throughout the day. Although this system lacks significant moisture, lake enhancement is expected to amplify snowfall totals in parts of Northeastern Ontario and the regions surrounding Lake Huron and Georgian Bay. We're anticipating overall snowfall accumulation of 10-20cm, with localized areas possibly seeing up to 25cm by Wednesday morning.

While the bulk of the snow will diminish by Wednesday, localized snow squalls could continue to dust the Grey-Bruce and Muskoka regions with an additional 5-15cm of snow by Wednesday's end. However, these higher amounts will be highly localized.

Snowfall has started in parts of Northwestern Ontario, with the system moving south and east overnight. Light snow is expected for most regions throughout Tuesday, except near Lake Superior, Georgian Bay, and Lake Huron, where lake enhancement will result in heavier snowfall.

Particularly northwest of Georgian Bay and east of Lake Superior, Tuesday morning and afternoon will see locally intense snow bands causing reduced visibility and rapid accumulation. These conditions will extend through parts of Northeastern Ontario and into Central Ontario.

By Tuesday night, we expect the system-induced snow to taper off shortly after midnight. However, with cold temperatures prevailing, lake effect snow is likely to continue into Wednesday. This includes a potentially strong snow squall in the Grey-Bruce area, reaching into parts of Simcoe County and the Northern GTA by Wednesday morning.

The snow squall is forecasted to be brief as a wind shift will cause it to move southward and gradually dissipate. Another bout of light snow is anticipated across Southern Ontario on Wednesday afternoon as lake-effect snow becomes more widespread due to the shifting wind direction.

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The heaviest snowfall, primarily due to lake enhancement, is expected east of Lake Huron and Georgian Bay. Areas like Owen Sound, Wiarton, Parry Sound, Huntsville, and Sundridge could see totals of 15 to 25cm by Wednesday's end. Owen Sound, in particular, may receive upwards of 30cm, especially if the Wednesday morning squall intensifies as some models suggest.

Neighbouring areas such as Bracebridge, Orillia, Collingwood, Hanover, Kincardine, and Tobermory are projected to receive 10 to 20cm of snow. However, due to the variability introduced by lake enhancement, snowfall distribution will be highly unpredictable, with some locations potentially receiving less than 10cm.

Locations like Goderich, Orangeville, Barrie, Peterborough, and Kingston should brace for 5 to 10cm of snow. These areas will benefit from some lake enhancement, but limited overall moisture will keep totals below 10cm.

Eastern, Southwestern Ontario, and the Golden Horseshoe, including the Greater Toronto Area and Extreme Southwestern Ontario, are expected to see about 5cm of snow over the next two days, with some areas receiving only a few centimetres.

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Northeastern Ontario, extending into Northwestern Ontario, could see 15cm to 25cm of snow by the end of Wednesday. This includes Sault Ste. Marie, Wawa, Marathon, Geraldton, Timmins, and Kirkland Lake.

The remainder of Northeastern Ontario will see totals between 10 to 20cm, though regions north of Georgian Bay like Elliot Lake and Sudbury may receive less than 10cm due to diminished lake enhancement.

Northwestern Ontario will experience lesser impacts, with Thunder Bay expecting 2 to 5cm of snow, while Kenora and Dryden will see less than 2cm.

Winter Is Not Done Yet! Parts of Southern Ontario Could See Up to 10-20cm of Snow by Monday

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Southern Ontario's recent spell of balmy weather made it feel like an early spring, yet winter has swung back into our forecast. A return of colder air has arrived just in time for the weekend, bringing a fresh batch of lake effect snow—aided by the unusually open waters after our mild winter.

Lake effect snowfall is expected to predominantly impact the southern shores of Lake Huron starting late Saturday and persisting into Sunday. The most affected regions could amass snow totals nearing 15 to 20cm by the end of Sunday.

Simultaneously, the outer bands of a system tracking up the Northeastern United States might deliver accumulating snow, primarily to Ontario's far eastern regions beyond Ottawa. These areas could see accumulations of 10 to 15cm by Monday morning.

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As of Saturday evening, we've witnessed a temperature dip across Southern Ontario, with expectations for the mercury to descend below freezing overnight. This shift sets the stage for lake effect snow development along the Lake Huron and Georgian Bay shorelines, particularly overnight and into Sunday morning.

Heavy lake effect snow is forecasted for areas stretching from Goderich to southward through Grand Bend and even into London, and south of Georgian Bay, encompassing the Meaford and Collingwood area.

The peak of this lake effect snow event is predicted for the pre-dawn hours on Sunday, continuing into early afternoon and gradually lessening by evening.

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Snow Squall Accumulation Disclaimer

Forecasting the exact snowfall accumulation for a specific location in a lake-effect snow event is extremely challenging. This is because of the highly localized nature of snow bands, which can lead to significant variance in totals even over short distances.

Therefore, you may notice our forecast shows significantly more snow than your weather app (including our own app). App-based forecasts often struggle with lake effect snow events due to their localized nature and reliance on data focused on larger macro-level weather events. This results in a failure to accurately capture the squalls, which operate at a micro-level, leading to intense snowfall totals.

Our forecast may still be off if the wind direction varies slightly from what the models predict, causing the snow squall band to form further north or south. That's why our forecasts use broader zones to account for this variability, meaning not everyone within these zones will see the significant totals. Essentially, we're indicating that a location within this area could see the forecasted amount.

The latest data indicate the most substantial snowfall will be found in areas like Goderich, Grand Bend, Lucan, and London, where totals may surpass 10cm, with localized areas potentially receiving 15-20cm. Elevated regions southwest of Collingwood are also likely to see over 10cm of snow.

Neighbouring regions such as Port Elgin, Wingham, St. Thomas, Meaford, and Collingwood might see up to 10cm, depending on the strength of the lake-effect snow. Lesser amounts, under 5cm, are anticipated for the rest of Southwestern Ontario and the Golden Horseshoe.

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Beyond the lake effect, heavy snow is forecasted to develop overnight in far Eastern Ontario as outer bands of precipitation from the slow-moving Eastern Seaboard system linger in the region.

Persistent snowfall will continue across areas east of a line from Kingston to Ottawa throughout Sunday, possibly continuing overnight before fizzling out just after Monday's sunrise.

Regions including Hawkesbury, Alexandria, and Cornwall could see totals exceeding 10cm by Monday morning. The area from Ottawa south to Brockville might approach snowfall close to 5cm. As we move westward, expected accumulations will quickly decrease, with less than 5cm forecasted due to the sharply declining precipitation gradient.

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Messy System Targets Ontario This Weekend With Significant Rain to the South and Heavy Snow to the North

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The opening week of March has been notably calm in Southern Ontario, with minimal active weather events and a generous serving of above-seasonal warmth and predominantly clear skies. A few rain spells have visited us over the last several days, with temperatures occasionally leaping into the 20s, setting records on Tuesday and Wednesday in some locations.

Yet, as we move towards the weekend, we anticipate a shift, with a looming system poised to bring substantial rainfall across Southern Ontario. In contrast, those in Northeastern Ontario should ready themselves for a considerable snowfall, with some areas potentially seeing up to 30cm.

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Following the departure of this system by late Saturday, a period of sub-freezing temperatures will return to Southern Ontario on Sunday, extending into Monday. This shift sets the stage for the possibility of snow accumulation in parts of Central Ontario, particularly Eastern Ontario and near Lake Huron and Georgian Bay, at the onset of next week.

Southwestern Ontario has already begun to experience heavy rain on Friday evening, anticipated to last into Saturday. The heaviest downpours are expected overnight and into the morning hours. The rain will start around midnight for Eastern and Central Ontario and is likely to persist into early Saturday afternoon.

Accompanying the rain on Saturday will be a surge of mild air, with daytime highs expected to reach the upper single digits, and potentially the low teens throughout Southern Ontario. While the Northern parts of the province will see a more resilient cold air mass, resulting in snow rather than rain.

Northeastern Ontario will see the onset of snow around midnight, with the mixing line expected near Elliot Lake to slightly north of Sudbury. Areas north of the line, including Chapleau and Timmins, will experience significant snowfall overnight into Saturday morning, with intense snow at times throughout the day.

Both the rain in the south and snow in the north will diminish as the evening progresses, as the system departs our region. By Saturday evening, a switch from rain to snow is possible in the northern regions of Central and Eastern Ontario. However, with the ground still saturated from previous rains and temperatures hovering just above freezing, significant accumulation is not anticipated.

Overnight into Sunday, light to moderate snowfall may occur in regions traditionally affected by lake-effect snow around Lake Huron and Georgian Bay. Eastern Ontario might also receive some flurries from the lingering bands of system-related precipitation. Currently, we predict a few centimetres of snow at most, though certain areas along the Lake Huron shore and south of Georgian Bay could receive up to 5-10cm. A more detailed forecast for Sunday's snow will be released on Saturday.

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Regarding total rainfall, Central and Eastern Ontario are set to receive the highest totals, with 25 to 40mm expected by Saturday's end, which may cause localized flooding. Widespread totals of 15 to 30mm are projected across most of Southern Ontario. Areas near the Golden Horseshoe, along the southern Georgian Bay shoreline, and over Algonquin Park could see a dry pocket leading to slightly less rain, with 10 to 20mm anticipated.

As for Northeastern Ontario, snow will be the dominant story with snowfall totals of 20 to 30cm in a broad swath encompassing Timmins, Kirkland Lake, Cochrane, and Kapuskasing. A sharp drop-off in accumulation is forecasted closer to the rain-snow mix to the south and drier areas to the north.

The Chapleau area can expect 10 to 20cm of snow, while less than 10cm is predicted for North Bay, Sudbury, Elliot Lake, and Sault Ste. Marie, with rain as the primary form of precipitation for those regions.

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Foggy & Warm Days Ahead for Southern Ontario: Widespread Dense Fog Starting This Weekend and Double-Digit Temperatures on Monday

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March has ushered in a tranquil period for Southern Ontario following the whirlwind of weather experienced in the final stretch of February. With temperatures climbing above the seasonal norm for the weekend, an area of fog has begun to descend across the region, foreshadowing a week that will start with several mornings blanketed in dense mist. While light drizzle is expected to accompany the fog, significant rainfall is not anticipated.

We are also watching the potential for what could be some of the warmest air we’ve seen this year so far across Southern Ontario starting Monday.

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As of Saturday afternoon, fog has started to materialize in parts of Southern Ontario. Current models predict that this fog will thicken as the day progresses into the night, with much of Eastern, Central, and Southwestern Ontario, along with the Golden Horseshoe, expected to face near-zero visibility conditions overnight and into Sunday morning.

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Sunday will see the fog dissipate to some degree after sunrise, but it may persist in certain areas throughout the day. This break will be short-lived, as a more extensive blanket of fog is forecasted to envelop almost all of Southern Ontario by Sunday evening, remaining into Monday morning.

This persistent fog could lead to school bus delays or cancellations on Monday, so it would be wise to prepare for potential disruptions. The fog is slated to make a return on Monday night, continuing into Tuesday, which could once again impact school transportation for a second consecutive day.

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The weather story of this week continues with a resurgence of mild conditions, particularly pronounced on Monday through Wednesday. A swath of the area will experience highs in the double digits, with the Windsor region potentially flirting with the 20°C mark on Monday for the second time this year!

As Tuesday gives way to Wednesday, steady rainfall is expected to sweep across Southern Ontario, predominantly in the latter half of Tuesday, persisting into Wednesday. Rainfall totals are forecasted to be modest, in the range of 5-10mm by Wednesday's end. Moreover, the potential for a thunderstorm on Tuesday cannot be discounted, although the severity is not anticipated to come anywhere close to what we saw last week.

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‘Snow Day’ Forecast: Snow Squalls Likely to Cancel School Buses in Parts of Southern Ontario on Thursday

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Snow squalls have made a comeback to the familiar snowbelt areas around Lake Huron and Georgian Bay, and they're expected to continue throughout the night into Thursday. With conditions resembling a blizzard and up to 30cm of snow anticipated overnight, it is highly likely that many school boards in the impacted areas will declare a 'snow day' for Thursday.

The likelihood of a snow day is highest in all of Grey & Bruce counties, as well as the west and central weather zones of Simcoe County, with a 90% chance of school bus cancellations. For surrounding school boards and along the rest of the eastern Lake Huron shoreline, the chances vary from 50 to 75%.

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Given that this event is highly localized to the snowbelt, widespread cancellations outside of the main affected region are not anticipated, as shown on our map. However, a few cancellations may occur in Eastern Ontario due to icy conditions remaining from this evening's flash freeze into the morning. These are more likely for the more rural school boards, for which we have assigned a 10% chance.

For the remainder of Southern Ontario, the likelihood of school bus cancellations for Thursday is very low.

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.

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From Record-Breaking Heat to Blizzard; Snow Squalls Could Dump Upwards of 15-30cm on Parts of Ontario by Thursday

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The last 48 hours have been a weather whirlwind across Southern Ontario, beginning with thunderstorms and the season's first 20°C temperature recorded in Windsor on Tuesday.

This brief 'heatwave' has abruptly ended, ushered out by a sharp cold front that sent temperatures tumbling on Wednesday. By overnight into Thursday morning, we're bracing for wind chills that could make it feel like it's in the -20s!

The return of Arctic air to Southern Ontario typically means one thing: Mother Nature is about to fire up the lake effect snow machine over the usual snowbelt regions. The upcoming day will be no exception as we anticipate intense snow squalls affecting the Lake Huron and Georgian Bay shorelines, potentially dumping 15 to 30cm of snow by Thursday's end. Accompanying the heavy snow will be strong wind gusts, leading to blowing snow and localized blizzard conditions over the next 24 hours.

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The cold front in question has already made its way across our region as of early Wednesday afternoon, with temperatures in Southwestern and Central Ontario swiftly falling below freezing. This trend is expected to persist, bringing even colder air by evening.

Lake effect snow is set to begin this afternoon, initially starting off as disorganized and light. Expect light to moderate snowfall along the Lake Huron and Georgian Bay shorelines through the afternoon and evening. In Northeastern Ontario, snow squall activity is underway, focusing on the southeastern shoreline of Lake Superior between Wawa and Sault Ste. Marie.

As we move into Wednesday evening, models predict a more intense, focused squall developing between Wiarton and Kincardine, extending over Georgian Bay to come in land around Simcoe County. The Sault Ste. Marie region will also face relentless snow squall activity through the evening and overnight.

This squall is particularly noteworthy due to its significant moisture content, benefiting from an optimal fetch across Lake Superior, Lake Huron, and Georgian Bay. Consequently, we expect high snowfall rates, with the potential for the band to reach far inland, possibly affecting parts of the Northern GTA.

Driving conditions in Grey, Bruce, and Simcoe Counties, among other regions, will become treacherous overnight into Thursday morning. With wind gusts of 60 - 80 km/h, near-zero visibility and rapid snow accumulation are anticipated, raising the possibility of highway closures overnight.

Further south, areas away from Lake Huron like Listowel and Hanover may experience more scattered, less intense lake effect snow compared to the squall to the north.

By sunrise on Thursday, the main snow squall is expected to begin dissipating, although it will likely persist through the morning and early afternoon. The shifting wind direction may cause the squall to drift, dispersing snowfall over a broader area.

Lake effect snow activity off Lake Superior and Lake Huron/Georgian Bay is anticipated to wind down by mid to late afternoon on Thursday, as a slight temperature rise creates conditions less conducive to lake effect snow development.

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Snow Squall Accumulation Disclaimer

Forecasting the exact snowfall accumulation for a specific location in a lake-effect snow event is extremely challenging. This is because of the highly localized nature of snow bands, which can lead to significant variance in totals even over short distances.

Therefore, you may notice our forecast shows significantly more snow than your weather app (including our own app). App-based forecasts often struggle with lake effect snow events due to their localized nature and reliance on data focused on larger macro-level weather events. This results in a failure to accurately capture the squalls, which operate at a micro-level, leading to intense snowfall totals.

Our forecast may still be off if the wind direction varies slightly from what the models predict, causing the snow squall band to form further north or south. That's why our forecasts use broader zones to account for this variability, meaning not everyone within these zones will see the significant totals. Essentially, we're indicating that a location within this area could see the forecasted amount.

The areas hardest hit in Southern Ontario are expected to be Wiarton, Owen Sound, Chatsworth, Meaford, Collingwood, and Barrie, with 15 to 30cm of snow accumulation possible by Thursday's end.

It's important to note that models significantly diverge on the strength of these squalls, with some indicating potential for up to 50cm of snow in localized areas. Thus, there's a possibility for some regions, especially if the squall remains stationary overnight and into Thursday morning, to experience higher than anticipated snowfall totals.

Surrounding areas such as Port Elgin, Hanover, Keswick, and Orillia are generally expected to see 10 to 20cm, although the snow accumulation gradient will be extremely tight, meaning some areas may see little to no snow.

Less than 10cm of snow is forecasted for the rest of Southern Ontario, with accumulations above 5cm confined to regions east of Lake Huron and around Lake Simcoe. Durham region could approach 10cm of snow, depending on the inland reach of the Georgian Bay snow squall. Eastern Ontario and the Golden Horseshoe are expected to see less than 2cm of snow.

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In Northeastern Ontario, snow from a system will continue affecting the northern regions, including Timmins, Kapuskasing, and Cochrane, with 20 to 30cm of snow possible.

Lake effect snow will be more localized, with Sault Ste. Marie anticipated to receive 15 to 30cm of snow before the squalls taper off late Thursday. The rest of Northeastern Ontario can expect widespread totals of 5-15cm, with some areas seeing up to 20cm.

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Flash Freeze Threatens Wednesday Afternoon/Evening Commute Across Southern Ontario

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After experiencing a series of thunderstorms and Ontario's first 20°C temperature of the season recorded in Windsor on Tuesday, we're on the brink of a significant shift as we head into Wednesday. It feels like we're at the peak of a roller coaster, about to dive back down into winter-like temperatures.

This transition will be marked by a sharp cold front, leading to a rapid decrease in temperatures. Expect to see temperatures plummet from the upper single digits or low teens to well below the freezing mark within just a few hours on Wednesday. With roads and surfaces still wet from previous rainfall, a 'flash freeze' is almost certain, where all moisture on surfaces will quickly freeze, turning to ice.

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The severity of the flash freeze will differ across regions, with Central and Eastern Ontario witnessing the most dramatic temperature drops — from near double digits to the freezing mark within an hour or two in the afternoon to early evening. In Southwestern Ontario and the Golden Horseshoe, the temperature will initially drop to just above freezing, with a more gradual descent toward the freezing mark. This difference in temperature change rate will significantly impact the flash freeze threat, with a slower onset for these areas.

Following the cold front, lake effect snow will begin to form around Lake Huron and Georgian Bay from Wednesday evening into Thursday. While specifics will be detailed in a separate forecast, it's likely that traditional snowbelt regions could see upwards of 20-30cm of snow by week's end. However, this snow won't linger, as milder air is forecasted to return by the weekend.

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Wednesday morning will greet you with temperatures well above seasonal, in the mid to upper single digits through Central and Eastern Ontario, and possibly even double digits in the southwest. This warmth is extraordinary for this time of the year, especially considering it will occur in the morning, typically cooler than peak daytime temperatures. Windsor, Chatham, and Sarnia could see temperatures ranging from 12 to 15°C, making them the expected hotspots.

The onset of change will start later in the morning as the cold front approaches. Much of Southern Ontario will still experience mild temperatures of 6 to 9°C, except along the Lake Huron shoreline, where temperatures will be closer to 3°C, and near-freezing on the Bruce Peninsula.

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Northeastern Ontario will display the stark contrast in temperature gradients. North Bay and Sudbury will enjoy continued warmth from the south, with temperatures of 2 to 6°C, while Elliot Lake and areas towards Temiskaming Shores will be among the first to experience the cold plunge raging from -3 to -12°C.

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By early afternoon on Wednesday, the cold air will start to dominate, pushing the warm air east and causing temperatures to drop below freezing across much of Southwestern and Central Ontario. The Grey-Bruce region will see temperatures between -3°C to -5°C by 1 PM. The freezing line will sweep across Central Ontario and the Golden Horseshoe early in the afternoon.

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Northeastern Ontario will see Sudbury's temperatures drop from 3-5°C in the morning to near -9°C by the afternoon. While North Bay will follow Sudbury’s lead by the mid to late afternoon hours.

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By 4 PM, the last areas to experience the drop will be in the Ottawa valley, with temperatures nearing 12°C in the Brockville and Cornwall area. The rest of Southern Ontario will have already experienced the temperature drop and will hover at or slightly below the freezing mark through the afternoon.

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As night falls, the entire region of Southern Ontario will see temperatures plummet, with Eastern Ontario experiencing the drop around dinner time. Expect temperatures to range from -3 to -5°C in Southwestern Ontario and the Golden Horseshoe, while Central Ontario might see temperatures dip into the negative double digits.

By Thursday morning, the cold will intensify, with wind chills potentially making it feel like the -20s in parts of Southern Ontario. Be sure to bundle up before heading out the door on Thursday!

‘Ice Day’ Forecast: Potential School Bus Cancellations on Wednesday in Southern Ontario Due to Expected Flash Freeze Risk

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After witnessing record-breaking temperatures and widespread thunderstorms on Tuesday, we're bracing for a drastic shift as Wednesday approaches. This shift will occur as a sharp decrease in temperatures beginning late Wednesday morning and lasting throughout the day.

Consequently, the rapid temperature drop—from double digits to below freezing in mere hours—will likely result in flash freeze conditions on the roads. Environment Canada has issued warnings regarding the flash freeze threat throughout Central and Eastern Ontario. Though the flash freeze is anticipated across all of Southern Ontario, the temperature decline will be more significant in areas under the warning.

Regarding school bus cancellations, the timing is particularly problematic as the temperature drop will not start until after the morning bus routes. This situation necessitates that school boards preemptively cancel afternoon bus services based on the forecast. Traditionally, they have relied on Environment Canada alerts for such decisions, and as of Tuesday evening, warnings have been issued only for Central and Eastern Ontario. The rest of Southern Ontario is under a special weather statement or no alert at all.

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Central Ontario has the highest likelihood of school bus cancellations, coinciding with the warnings in effect and specifically citing Wednesday afternoon for the expected flash freeze. We've assigned these areas a 75 to 90% chance of an 'ice day,' confident that the warning will suffice to prompt bus cancellations.

For Eastern Ontario, where the warning indicates a flash freeze during the evening, it seems less probable that school boards will cancel buses. Here, the chances range from 25-50%; we can't dismiss the possibility entirely, but it appears to be unlikely.

Those in Southwestern Ontario will encounter the temperature dip earlier in the day, so we've estimated a 25 to 50% chance of an 'ice day' there since it will likely have a larger impact on the afternoon bus run. These odds could increase substantially if Environment Canada extends the flash freeze warning by the morning.

As for the Golden Horseshoe area, the decision by school boards to cancel buses is more uncertain; they typically require more extreme conditions, such as significant snowfall, for cancellations. Here, the probability of cancellations ranges from 5 to 10%.

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.

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Rare February Severe Thunderstorm Risk for Parts of Southern Ontario on Tuesday

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As we bid farewell to February, Southern Ontario is set for a wild weather ride, with a rapid-fire succession of seasons in the span of just a few days. This climatic roller coaster is set to take off on Tuesday, bringing an influx of temperatures that are notably higher than what we're used to this time of year. Alongside the warmth, we brace for another hallmark of spring: the threat of thunderstorms.

Looking ahead, we have two distinct thunderstorm risks within a 48-hour window. The early birds in Southern Ontario might be in for a surprise with the first bout of storms expected during Tuesday's morning hours. Coming later in the day, there's the potential for more storm activity that could approach severe levels in the late afternoon and evening.

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As dawn breaks on Tuesday, we expect to see scattered showers and thunderstorms bubble up during the mid to late morning in Southwestern Ontario. Given the environment and minimal energy, these initial storms aren't likely to reach severe thresholds, but they may still pack a punch with lightning, potential for small hail, and strong wind gusts.

These storms will continue to track to the northeast toward Central Ontario and around Georgian Bay, lasting through the morning and into the early afternoon. Throughout the day, a surge of warm air from the southwest will see temperatures soaring into double digits across Southern Ontario.

While everyone across Southern Ontario will feel the heat on Tuesday, the highest temperatures will be found in Deep Southwestern Ontario, affecting locations like Windsor, Chatham, and Sarnia. The extent of this warm spell varies across the different weather models, but don't be shocked if Windsor sees its first 20°C day of the year on Tuesday!

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Progressing into the late afternoon, the escalating heat is likely to stir up atmospheric instability, setting the stage for thunderstorms starting late Tuesday afternoon. These storms are forecasted to pop up to our west, over Michigan and neighbouring states, where a robust environment for severe storms could take shape. However, this forecast remains up in the air, with some of the latest models suggesting storm development could be pushed back to the evening or even overnight which would lead to a lower severe threat.

If storms do materialize, we can't dismiss the possibility of an isolated severe storm tracking into Deep Southwestern Ontario. The primary hazards would be large hailstones, possibly as big as quarters, wind gusts reaching 90 km/h, and heavy downpours. While the tornado risk is not entirely absent, it's expected to remain primarily a concern on the American side of the border.

Another consideration is the lake temperatures this early in the season. While this winter hasn’t been cold by any measure, the lakes are still fairly cold compared to what we would see in the late spring or summer. Colder lakes have a tendency to drain storms of their energy as they cross over the lake and into our region. However, the stretch between Sarnia and Windsor is less shielded by the lakes, leaving it more vulnerable to severe storms crossing the border with little hindrance.

Storms are expected to persist across Southern Ontario into the overnight hours, leading into Wednesday morning. There is a questionable isolated severe risk for the Lake Erie shoreline and into the Niagara region just after midnight that is being picked up by some models.

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Apart from thunderstorms, Tuesday night is shaping up to be unusually mild, rolling into Wednesday morning with temperatures climbing overnight to remain in the double digits for much of Southern Ontario.

But don't be deceived by the unseasonably warm start to your Wednesday. A stark cold front is scheduled to slice through Southern Ontario from the northwest to the southeast beginning late Wednesday morning. This will result in a drastic drop in the temperature from the mid-teens to sub-zero levels in a matter of hours.

The potential for a flash freeze is particularly concerning, especially considering the preceding rain from the storms. Roads are expected to swiftly transition to treacherous sheets of black ice, complicating Wednesday afternoon's commute.

Stay tuned for more comprehensive details on the flash freeze threat, along with an update on the potential for snow as we move into late Wednesday and Thursday.

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