Toronto’s Storm of the Century: Remembering Hurricane Hazel 70 Years Later

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Overhead view of Raymore drive in Toronto following hurricane hazel, courtesy of Toronto and Region Conservation Authority.

It was on this day 70 years ago, in 1954, that the now infamous Hurricane Hazel hit Southern Ontario and caused catastrophic damage to Toronto. It is considered the area’s worst natural disaster and has shaped development for years to come. The storm produced winds up to 124km/h and dumped over 200mm of rain in just 24 hours; left 81 people dead and over 4000 families homeless, 1868 of those families in Toronto; and caused over $135 million in damages in Ontario ($1.5 billion by today’s standards). Hazel changed the way conservation authorities operate across Ontario and those impacts are still felt to this day.

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Hurricane Hazel's Path, October 14-15, 1954, Courtesy of the National Weather Service.

Hurricane Hazel was first identified on October 5, 1954 by a Hurricane Hunters aircraft from Puerto Rico which located it just east of the island nation of Grenada in the West Indies. The plane estimated that the storm was already a Category 2 hurricane with winds estimated at 160km/h, but this value was more recently revised to 105km/h, making Hazel a Tropical Storm at the time, during reanalysis of former hurricane seasons by NOAA. Hazel intensified following the Hurricane Hunters mission and it made its first landfall over Grenada on the evening of the 5th as a Category 1 hurricane with winds estimated at 120km/h.

From there, Hazel tracked west-northwestward off the northern coast of Venezuela for the next few days, gaining strength along the way. Late on October 9th, Hazel gained Major Hurricane status with winds estimated at 195km/h. The next day, the storm made a sharp turn and started churning northeastward, where it eventually made two separate landfalls on Haiti’s west coast, initially over the Tiberon Peninsula as a Category 3 with winds estimated at 195km/h in the pre-dawn hours on the 12th and then as a Category 2 with estimated winds of 160km/h later that same evening over the northern peninsula. Hurricane Hazel killed up to 1000 people in Haiti and devastated the economy, destroying 40% of the nation’s coffee trees and 50% of the cacao crop.

Following its second landfall in Haiti, Hurricane Hazel curled northwestward and made its fourth total landfall in Inagua, an island in the Bahamas, less than 18 hours later on the morning of the 13th. The storm maintained its Category 2 strength between the two landfall occurrences, hitting the Bahamas with winds estimated at 160km/h.

Beyond the Bahamas, Hazel gained speed and reintensified, becoming a Category 4 hurricane on the evening of October 14th. Just before noon on October 15th, Hazel made its fifth and final landfall near the border of North Carolina and South Carolina as a Category 4 hurricane with sustained winds of 215km/h and gusts up to 240km/h. Hazel quickly transitioned to a post-tropical cyclone, but it maintained hurricane-force winds as it quickly pushed through D.C., Pennsylvania, New York, and towards the Canadian border. The storm killed 95 Americans and caused over $1.5 billion of damage by today’s standards.

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Surface Chart from 8:3pm ET showing the location of Hazel over Southern Ontario, Courtesy of the National Weather Service.

As Hazel made its way northward through the States, Canadian authorities began issuing warnings to the general public, but most people didn’t know how to prepare for a hurricane. The storm began to weaken over the Allegheny Mountains in West Virginia and meteorologists expected it to dissipate, however the opposite happened. Instead, Hazel encountered a low-pressure system over western New York and intensified just before it crossed into the Niagara Peninsula.

Hurricane Hazel was a post-tropical Category 1 storm that brought severe wind gusts of up to 124km/h to a large portion of Southern Ontario on October 15th, but the winds were not the main concern from the storm. By the evening rush hour, the winds began to die down, but according to Chief Meteorologist Brian Turnbull, the worst of the storm was yet to come. The days leading up to Hazel’s arrival were quite wet so when the heavy rainfall began in the late afternoon, it didn’t take long for flooding to begin. Significant deforestation and development on the saturated flood plains across Toronto could not contain the over 200mm of rain that fell in 24 hours which resulted in many rivers overtopping their banks, with water levels rising by up to 8 metres. The Humber River, in particular, became a deadly torrent through the city, washing away roads, bridges, and entire homes. Overall, the storm dumped 181.6 billion litres of rain on the City of Toronto.

In total, 81 people lost their lives from Hurricane Hazel, mostly in the west end of Toronto. Across Southern Ontario, approximately 4000 families lost their homes, 1868 of which were in Toronto. Raymore Drive was hit particularly hard with 14 homes being washed away, killing 35 people. Fortunately, the death toll could have been much worse if not for the heroics displayed by many police officers, firefighters, and ordinary citizens who worked tirelessly trying to save those who became stranded. Sadly, five firefighters lost their lives when trying to rescue trapped motorists.

The effects of Hurricane Hazel were felt beyond Toronto. Significant flooding was experienced in communities as far west as London and north to Georgian Bay as the storm progressed northwards to James Bay, where it eventually dissipated.

Members of the Harbour Patrol Rescue a man from the Don River, courtesy of the Canadian Encyclopedia.

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In the aftermath of Hurricane Hazel, many changes were made to conservation authorities across Ontario, especially in the Greater Toronto Area.

An intensive plan was put in place by conservation authorities, along with both the municipal and provincial governments, for flood control and water conservation in order to limit loss of life and property from future extreme weather events. As part of this plan, flood control facilities were inspected, upgraded, or built alongside additional dams and reservoirs to control and monitor water levels. A flood forecasting and warning system was also a large component to the plan.

An amendment was made to the Conservation Authorities Act that allowed individual conservation authorities to obtain and control vulnerable areas to be used for conservation and recreation. As a result, many homes were cleared from low-lying areas and greenbelts were created within watersheds. This included the expropriation of most remaining properties on Raymore Drive by the Metro Toronto and Region Conservation Authority which was turned into parkland, now called Raymore Park.

As we look back on the anniversary of this tragic event, we want to remember those that were lost and all of the efforts that have been put in place since to prepare for future extreme weather events. The City of Toronto has seen many flooding events since Hurricane Hazel, and it will continue to do so for many year. However, major floods in 2013 and more recently in 2024 show that more work still needs to be done.

The G. Ross Lord Dam, One of the Many Flood Control Measures in Place Across Toronto, Courtesy of the Toronto and Region Conservation Authority.

Sources:

https://www.aoml.noaa.gov/hrd/hurdat/hurdat2.html

https://www.heritage-matters.ca/articles/hurricane-hazel-50-years-later

https://www.heritagetrust.on.ca/pages/programs/provincial-plaque-program/provincial-plaque-background-papers/hurricane-hazel

https://www.hurricanehazel.ca/ssi/evolution_flood_control.shtml

https://www.thecanadianencyclopedia.ca/en/article/toronto-feature-hurricane-hazel

https://www.thecanadianencyclopedia.ca/en/article/hurricane-hazel

https://www.trca.ca/news/hurricane-hazel-70-years/

https://www.weather.gov/mhx/Oct151954EventReview

Post-Thanksgiving Cool Down to Bring Season’s First Flurries to Parts of Southern Ontario on Tuesday

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The chill is definitely in the air following the Thanksgiving long weekend across Ontario, with overnight lows hovering around the freezing mark in many areas over the past few days.

This is a sharp change from the mild autumn weather we experienced throughout September, which has led to a noticeable delay in the changing of the leaves. While the trees are still taking their time to show off their fall colors, other signs of the season are on the way over the next few days.

Most notably, the combination of colder air and the warm waters of the Great Lakes will create ideal conditions for lake-effect precipitation to develop off Lake Huron and Georgian Bay.

While most areas will see lake-effect rain, it could get cold enough along the higher elevations of the Dundalk Highlands, south of Georgian Bay, for some wet flurries to appear on Tuesday.

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Additional precipitation is expected to move into Northeastern and Central Ontario by late Tuesday. As temperatures approach the freezing mark, some areas may see a transition to wet snow. However, significant accumulation is not expected, as the snow will likely melt almost immediately due to the warm ground, which remains above freezing.

For those who miss the milder weather, there’s no need to worry—there’s a warm-up on the way as we head into the weekend and early next week. Some areas could see daytime highs reaching the upper teens or even low twenties, which is well above the seasonal average for this time of year.

PRECIPITATION TYPE DURING THE DAY ON TUESDAY - MAP FROM WEATHERBELL

On Tuesday morning, most places will wake up to temperatures near the freezing mark, but daytime highs are expected to gradually rise into the mid to upper single digits. The higher elevations around Orangeville and Shelburne may struggle to climb above freezing, holding onto near-freezing temperatures throughout the day.

Lake-effect rain is expected to continue south of Georgian Bay throughout Tuesday, and some wet snow could mix in over the Dundalk Highlands during the day. This potential for flurries will be highly localized to the higher elevations between Owen Sound and Orangeville, while areas outside this region are likely to avoid the season’s first snowfall for now.

With temperatures hovering near or just above the freezing mark, significant accumulation is unlikely, as most of the snow will melt upon contact with the ground. However, there is a chance of a few wet, slushy centimeters in very localized areas.

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PRECIPITATION TYPE DURING TUESDAY night - MAP FROM WEATHERBELL

As we move into the evening and overnight hours, temperatures will again drop to near the freezing mark across Central, Eastern, and Northeastern Ontario. With scattered showers arriving from the north and east, there is a possibility that some of this precipitation could fall as wet flurries overnight and into early Wednesday morning.

Accumulation will remain a challenge due to the relatively warm ground. However, those in Huntsville, Algonquin Park, and the Ottawa Valley might catch a glimpse of their first snowflakes of the season. The chance of snow will diminish by late Wednesday morning as lake-effect precipitation weakens and any lingering showers move out of the region.

As mentioned earlier, we’re expecting a gradual warm-up for the rest of the week, though the mornings will still start off chilly, with temperatures in the single digits. The real warming trend will kick off on Friday, with temperatures climbing into the upper teens and possibly even approaching the low twenties in Southwestern Ontario and around the Golden Horseshoe.

This milder weather is expected to continue through the weekend and into early next week.

Ontario’s Potential Last Severe Thunderstorm Risk of the Year on Sunday to Usher In a Chilly Start This Week

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Get ready, Ontario! While we've been enjoying a relatively mild start to fall, aside from a few exceptions, a significant change is on the horizon. As we head into the first weekend of October, it looks like Mother Nature is gearing up to bring in more seasonally appropriate weather. But, true to Ontario's reputation, it won’t happen quietly.

The weekend so far has seen relatively calm weather across Southern Ontario, with many areas enjoying pleasant temperatures in the mid to upper teens. This marks a shift from the consistent 20°C-plus days we experienced through much of September. While it's been nice, things are about to take a turn. We’re expecting a sudden surge of warmer air on Sunday, and that warm-up could set the stage for some potentially severe weather as we move into the morning and afternoon hours.

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This brief October "heatwave" could push temperatures close to 20-25°C in Deep Southwestern Ontario and across the Golden Horseshoe. For those of you in Central and Eastern Ontario, however, don’t expect to feel much of this warmth. A stubborn pocket of cooler air is going to dig in, holding temperatures in the mid-teens across that region, keeping it much cooler than the rest of the province.

Unfortunately, this warm-up isn’t all sunshine. It will come hand-in-hand with some unsettled weather. A potentially strong line of thunderstorms is expected to cut across Southern Ontario on Sunday morning and afternoon. The latest data suggests that this line of storms could develop over Lake Huron by late morning and track eastward, making its way onshore just east of Lake Huron and Georgian Bay.

SIMULATED RADAR @ 12 PM ON SUNDAY - MAP FROM WEATHERBELL

There is still some uncertainty regarding the intensity of these storms. The early timing and limited warm air this far north may impact how severe the storms get. However, the atmosphere seems primed to support at least a marginal severe threat. We could see strong wind gusts, potentially reaching 90 km/h, and even hail up to quarter-size. There’s also a possibility that the risk level could be upgraded to slight by morning if conditions appear more favourable.

There is a low tornado risk—while it can’t be completely ruled out, the messy, linear storm structure might limit the chances of an isolated tornado forming. Still, it’s always better to stay cautious when severe weather is in the forecast.

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This line of storms will continue pushing eastward through the Golden Horseshoe and areas east of Lake Simcoe by early to mid-afternoon. There’s potential for some intensification as the day progresses, or we could even see additional storms developing in the wake of the initial line. The zone between Bancroft, Peterborough, and Durham Region, and possibly stretching into Niagara, seems to have the highest risk for severe weather, should the conditions align more favourably.

By the late afternoon, the bulk of the storm activity will shift into the United States, where further severe weather could develop over Upstate New York and Pennsylvania. As a result, the storm threat across Southern Ontario should rapidly diminish by early evening. Given the time of year and the fact that cooler weather is set to follow, it’s quite possible that this could be our last widespread severe weather event of the season.

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ESTIMATED TEMPERATURE @ 7 AM ON TUESDAY - MAP FROM WEATHERBELL

Speaking of cooler weather, expect a noticeable drop in temperatures as we start the new week. By Monday and Tuesday, much of Southern Ontario will feel the chill, with daytime highs struggling to climb into the mid-teens.

Central and Eastern Ontario could be even cooler, with some areas potentially stuck in single-digit highs. The nights will be even colder. On both Tuesday and Wednesday mornings, some regions in Central and Eastern Ontario could dip below 0°C, bringing a risk of frost for a large portion of Southern Ontario.

At this point, we’re not expecting s-word to enter the forecast this week at least in Southern Ontario, but the cold snap will certainly make it feel like fall has truly arrived. So, if you’ve been holding off on packing away your summer wardrobe, it might be time to start thinking about those cozy sweaters and heavier jackets.

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LONG RANGE TEMPERATURE FORECAST FOR THANKSGIVING SUNDAY - NOTE: THIS WILL LIKELY CHANGE! (MAP FROM WEATHERBELL)

However, there might be some good news as we look ahead to the Thanksgiving long weekend. Early indications suggest a potential return of warmer air by next weekend, bringing with it another temperature boost. Some models hint at temperatures pushing 20°C once again in parts of Southern Ontario, which would be quite a surprise for Thanksgiving, given that we’ve seen flurries on the holiday in previous years!

It’s still too early to say for sure, though, as the forecast could change over the coming days. But for now, we’ll remain optimistic about the possibility of a pleasant, mild Thanksgiving weekend. As always, we’ll be monitoring the situation closely and will provide a more detailed Thanksgiving preview later this week.

Fall Colours Reach Peak in Parts of Southern Ontario Heading Into First Weekend of October

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Fall colours have been slow to arrive in parts of Southern Ontario due to a relatively mild September, but as we move into the first weekend of October, the transformation is starting to take hold. Several parks are now within their 'peak' fall colours range, providing excellent viewing opportunities.

The best spots to see the vibrant colours this weekend will be in Central and Eastern Ontario, as well as Bruce County along the Lake Huron shoreline. Many parks in these areas are showing between 40-50% colour change, with some even nearing full transformation!

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Note: The above map is extrapolated using data from OntarioParks.ca, but some parks may not have updated their latest report yet. As such, the actual colour change in your area may be further along than currently reported.

All provincial parks in Southern Ontario are reporting at least 10% colour change, indicating that the seasonal shift is well underway. However, it could take another week or two for many areas to reach their 'peak.'

With Thanksgiving just around the corner, it’s likely that much of Southern Ontario will be hitting its peak fall colours, making it the perfect time to enjoy the beauty of the season during the long weekend.

For those wondering, 'peak' fall colours occur when at least 60% of the leaves have changed. Based on this, Algonquin and Mikisew Parks are officially in their peak, though this won’t last long. Mikisew is already reporting 70% of its leaves have fallen, so Algonquin might be a better option for now, with only 20% leaf fall reported.

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Several provincial parks are currently showing between 40-50% colour change, mostly in Central and Eastern Ontario:

  • Arrowhead (50%)

  • Charleston Lake (50%)

  • Frontenac (50%)

  • MacGregor Point (50%)

  • Sturgeon Bay (40%)

  • Darlington (40%)

  • Turkey Point (40%)

  • Murphys Point (40%)

  • Bon Echo (40%)

  • Silent Lake (40%)

  • Driftwood (40%)

These parks are offering good chances to catch the fall display, and since the data can be a few days old, they may already be approaching peak colours by the weekend.

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The remaining parks in Southern Ontario are reporting 20-30% colour change, especially around Lake Ontario and Southwestern Ontario near Lake Huron.

Parks like Pinery, Awenda, Presqu’ile, Forks of the Credit, and Port Burwell are still at about 10%, but with cooler fall weather settling in, this will likely change quickly in the coming days. The peak for these parks is expected to arrive in 10-15 days, just in time for Thanksgiving weekend or shortly after.

Stay tuned for more updates as we continue to track the progress of fall colours across Southern Ontario!

‘Strong’ Geomagnetic Storm Takes Aim at Earth; Northern Lights May Dazzle the Skies Across Canada on Thursday & Friday

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One of the most powerful solar flares in recent years erupted from the sun on Tuesday evening, classified as an X7.1 flare. Initially, it was unclear whether this flare had produced a coronal mass ejection (CME), which is a large expulsion of plasma and magnetic field from the sun’s corona.

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However, data that came in later confirmed that a CME was indeed produced and, more importantly, appears to be Earth-directed. This means that the CME is expected to impact our planet, setting off the possibility of a ‘strong’ geomagnetic storm and potentially bringing the northern lights much farther south than usual across Canada to close out the week.

The exact timing of the CME's arrival, however, remains somewhat uncertain. Forecast models suggest it could arrive anywhere between late Thursday and early Saturday. The CME might even come in multiple waves, according to the latest data.

If this happens, we could be in for two consecutive nights of auroras lighting up the skies—if the conditions align perfectly! While the Northern Lights are never guaranteed, the next couple of nights offer a decent chance to catch a breathtaking display, depending on where you are located.

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The Space Weather Prediction Center (SWPC) has issued a Geomagnetic Storm Watch, with the CME expected to reach Earth between Thursday and Saturday. Based on the latest observations, this CME could trigger G1 (minor) to G3 (strong) geomagnetic storm conditions.

The SWPC’s latest forecast predicts that a 'strong' (G3) geomagnetic storm may unfold late Thursday evening into the early overnight hours, followed by a potentially more prolonged geomagnetic storm ranging from ‘moderate’ (G2) to ‘strong’ (G3) on Friday night into Saturday morning.

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A G2 to G3 storm is strong enough to make the northern lights visible across much of Canada, especially if conditions are just right. In the past, storms of this magnitude have allowed the auroras to be seen as far south as Southern Ontario, and in some cases, even into the northern United States. In fact, the SWPC notes the possibility of the auroras being visible as far south as parts of the lower Midwest and Oregon in the U.S.

That said, space weather forecasting comes with some inherent uncertainty. The exact timing of a CME’s arrival can vary, and its intensity is often unknown until a few hours before it strikes Earth. There is usually a 12- to 24-hour window for the CME’s arrival, which means that although the current forecast favours North American viewing on Thursday and Friday nights, the event could just as easily occur during daylight hours, rendering it invisible to viewers in North America and giving those in Europe a better chance at catching the show instead.

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Aside from timing, cloud cover will also be a crucial factor in determining whether you'll have a good view of the northern lights. As of now, fairly clear skies are expected across much of southern Canada on Thursday night. Specifically, areas of Atlantic Canada, Southern Quebec, and Southern Ontario are forecasted to have little to no cloud cover during the overnight hours, which is ideal for aurora viewing.

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Further north, however, there could be widespread cloud cover that might obstruct the view around James Bay in Northern Ontario and Quebec. Similarly, Northwestern Ontario could see some cloudiness, with the exception of a pocket near the International border around Thunder Bay.

In Southern Manitoba, skies look clear south of the Interlake region, though clouds will likely impact Northern Manitoba and Saskatchewan.

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For Western Canada, Southern Saskatchewan and Southeastern Alberta are expected to have the clearest conditions. Meanwhile, much of British Columbia, along with central and northern Alberta, could see cloud cover that may limit visibility.

Check out our free app, Instant Weather for a more in-depth cloud coverage forecast specific to your exact location.

If you’re planning to watch for the auroras, another factor working in your favour this time around is the moon phase. Unlike last month’s aurora event, the moon is currently near 0% full, as we’ve just had a new moon on Tuesday night. This means that there won’t be any moonlight competing with the northern lights, making it easier to spot even faint auroras.

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When it comes to where the northern lights might be visible, it all depends on the strength of the geomagnetic storm and how it interacts with Earth’s magnetic field. Historically, during a 'strong' (G3) storm, auroras are most visible across northern Canada, including Northern Quebec, Far Northern Ontario, the Prairies, and parts of British Columbia. In these regions, the northern lights could be visible overhead and bright enough to see with the naked eye.

In southern regions, including Northeastern Ontario (Sault Ste. Marie, Sudbury, and North Bay), as well as parts of Quebec, there’s a chance of seeing the auroras overhead or just above the horizon.

This could extend into northern parts of Southern Ontario, including Muskoka, Algonquin Park, and the Ottawa Valley. However, depending on the storm's strength, auroras may only be visible along the northern horizon, and you might need a camera to capture them, as they may not be strong enough for the naked eye.

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For the rest of Southern Ontario and into Atlantic Canada, if the auroras appear, they will likely be on the northern horizon. Here, too, you may need a camera or smartphone to capture the lights, as they may be too faint to see without assistance.

Remember, light pollution can greatly impact your ability to see the northern lights, especially in urban areas. For the best viewing experience, it’s essential to get away from city lights. A resource like DarkSiteFinder can help you locate areas with low light pollution for optimal aurora viewing.

Northern Lights Timing

Many are accustomed to the precise scheduling of weather events, from thunderstorms and winter weather to solar eclipses, where timing is crucial. It’s understandable, then, that there’s a desire for a similar pinpoint timing for the best viewing of the aurora. However, the reality of predicting the best time to view the northern lights is not so straightforward.

Here’s the deal: Unlike weather events driven by terrestrial conditions, the aurora is influenced by solar activity, which is far less predictable. We can estimate that the northern lights are best viewed from just after sunset to just before sunrise, provided the skies are dark and clear. Beyond that, precise timing for peak aurora activity is challenging to forecast with current technology.

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Space weather forecasting doesn't yet allow us to predict exactly when solar energy will impact Earth. We know it's coming, but how and when it interacts with our planet's magnetic field can vary. Often, we only have a few hours' notice before the solar energy is detected by satellites.

Furthermore, the intensity of the northern lights can fluctuate significantly over short periods. You might have noticed this variance if you've observed the lights before—periods of dim activity suddenly bursting into vibrant colors. This is due to the variable concentration of solar particles interacting with our atmosphere.

While we can inform you a few hours ahead when conditions are likely to be good, predicting the exact peak of aurora activity is akin to forecasting the peak of a meteor shower; we know the best night but not the best hour.

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After Devastating the Southeastern United States, Is Helene Coming to Canada?

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Satellite Image of tropical storm Helene from September 27th at 10:21am EDT, Courtesy of Colorado state university.

After making landfall as a major Category 4 Hurricane late last night and its subsequent path of destruction across Florida, Georgia, and the Carolinas, many in Ontario are wondering if we will feel the impacts of Helene closer to home over the weekend. Helene has since weakened to a tropical storm, but it remains a massive storm with far reaching impacts.

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Helene has made its way well inland over the past 12 hours, with its low pressure centre currently situated over the Southern Appalachians. Despite still being located so far south, light cloud cover from the storm has made its way into Southwestern Ontario and the Niagara Region. This cloud cover has been responsible for a fabulous display of sun halos across the region this morning!

The storm will continue to gradually track to the northwest this afternoon before stalling out over the Tennessee Valley overnight, where it will encounter and merge with another low. The lack of motion in the storm will unfortunately bring even more rainfall and further exacerbate the extreme flooding and landslide situation already being seen throughout the Southern Appalachians and bring that into the Ohio and Tennessee Valleys.

In Ontario, the cloud cover from Helene will push deeper into the province this afternoon and light rain can be expected in Southwestern Ontario, from Windsor through London and into Niagara, beginning overnight tonight and continuing through the weekend. Much of the rest of Southern Ontario can expect a dreary weekend as the cloud cover settles in.

The storm will actually travel in a loop, known as the Fujiwhara Effect, while it merges with the second low and by Sunday, it is expected to finally start moving eastward towards the Atlantic and then northeastward along the Eastern Seaboard, where it expected to begin to dissipate.

Forecast Tracks from different models for Helene, Courtesy of Tomer Burg.

Isolated Storms Could Bring Tornado Risk to Central Ontario and GTA on Wednesday

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As we near the end of what has been a relatively quiet month for weather across Southern Ontario, we’ve been locked in a pattern of calm conditions and unseasonably warm temperatures. But now, as we enter the first week of autumn, a shift is on the horizon!

Rainy weather has returned across much of Southern Ontario over the past few days, and unsettled conditions are expected to continue into Wednesday. There’s also potential for severe weather during the late morning, extending into the afternoon.

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RAINFALL WARNING (IN GREEN) ISSUED BY ENVIRONMENT cANADA

We’re already seeing pockets of heavy rain and thunderstorms overnight, which are expected to persist until sunrise. Environment Canada has issued rainfall warnings for some areas, where localized amounts of up to 50 mm are possible.

While it's uncertain, some models indicate a slight tornado risk in the morning, particularly around the Golden Horseshoe and Niagara Region. Though this is unlikely, it’s still worth noting.

The timing of when these overnight storms clear out will be key in determining the risk for later in the morning and afternoon. According to the latest models, most storms should dissipate by sunrise, allowing the atmosphere to become more unstable heading into the late morning.

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From around 11 AM through early afternoon, conditions could become favorable for isolated thunderstorms. The strongest setup is expected around Lake Simcoe, extending into the Muskoka and Haliburton regions.

While most storms are expected to remain non-severe, there is a chance of isolated tornadoes, along with marginally severe wind gusts and hail up to the size of quarters.

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The Greater Toronto Area and Niagara Region are under a marginal risk for severe weather, primarily due to the potential for an isolated tornado during the afternoon and early evening. This marginal tornado risk also extends into Algonquin Park and parts of southwestern Quebec.

It’s important to keep in mind that this forecast has a high bust potential—some models show little storm development during peak hours of instability. This forecast assumes storms will develop during the afternoon, but we may need to update and downgrade the risk in the morning if it looks less likely that storms will form.

First Day of Autumn Arrives as Central and Eastern Ontario Approaches Peak Fall Colours

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As we entered September, it seemed like Mother Nature was eager to shift from summer to fall, with temperatures dropping to near freezing and even some northern areas witnessing the first snowflakes of the season.

But since then, the weather has taken a complete 180. Over the past few weeks, Southern Ontario has experienced a consistent pattern of above-seasonal temperatures and minimal precipitation. This unusual warmth for this time of year has slowed down the transition to fall colours across the region.

With the Autumn Equinox taking place early Sunday morning, we are officially in autumn, both meteorologically and astronomically. As we move deeper into the season, we’re starting to see some notable shifts in fall foliage, especially in Central and Eastern Ontario, according to the latest data.

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If you're looking to catch the fall colours this week, your best bet is to head to higher elevations in Central and Eastern Ontario. Provincial parks such as Mikisew, Algonquin, and Bon Echo are reporting that around 40% of the leaves have started their transformation. The higher elevations experience slightly cooler overnight temperatures, which accelerates the colour change compared to other areas.

Note: The above map is extrapolated using data from OntarioParks.ca, but some parks may not have updated their latest report yet. As such, the actual colour change in your area may be further along than currently reported.

The ‘peak’ fall colours occur when at least 60% of the leaves have changed. With these parks now at 40%, we’re likely just a week or two away from peak viewing, perhaps as early as next weekend.

We’re also seeing some colour change along the Bruce Peninsula and throughout many parks in Central and Eastern Ontario, where about 30% of leaves have started changing. This includes parks like Sauble Falls, Arrowhead, Sturgeon Bay, Silent Lake, Frontenac, and Murphys Point.

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For the rest of Southern Ontario, there is some minor colour change being reported, with 10-20% of leaves beginning to turn. However, peak colours are still several weeks away in these areas.

An important note: The calm weather over the past few weeks has allowed trees to hold onto most of their leaves. Without any significant wind events, the leaf fall percentage is averaging around 10-20%. If these calm conditions continue, we should see a vibrant display of colours in the weeks ahead.

Looking at the medium to long range forecast, we’re expecting slightly above-seasonal temperatures to continue through the rest of September. This could mean peak fall colours might arrive later than usual this year, although it’s hard to say for certain. We do anticipate more active weather this week, with several rounds of heavy rain possible, which could potentially knock some leaves off the trees.

Eyes to the Sky! Northern Lights Could Make an Appearance Across Canada on Monday

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A powerful solar flare, reaching an impressive X4.5 rating, erupted on Saturday, sending an Earth-directed coronal mass ejection (CME) into space. This CME is expected to impact our planet, sparking geomagnetic storm conditions that could bring the northern lights much farther south than usual across Canada on Monday.

As with most space weather events, there is some uncertainty regarding the exact timing of the CME's arrival. According to the latest data, the strongest storm conditions are anticipated during the mid to late morning hours on Monday, gradually weakening throughout the day. This suggests the best viewing opportunity for the auroras may occur in the pre-dawn hours, particularly in Western Canada.

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However, this isn’t set in stone. Space weather forecasting can be tricky, and the CME might arrive later than expected, which would actually be the ideal outcome for North American skywatchers. A delayed arrival could mean a spectacular display of the northern lights over large portions of the country on Monday night.

The Space Weather Prediction Center (SWPC) is forecasting a "strong" geomagnetic storm (G3 on a scale of 5) to develop sometime on Monday. A G3 storm is potent enough to make the northern lights visible across much of Canada, provided the conditions align just right.

Historically, storms of this strength have allowed auroras to be seen as far south as Southern Ontario, and sometimes even into northern parts of the United States. In fact, the SWPC mentions the possibility of auroras being visible as far south as Pennsylvania and Iowa.

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Based on the SWPC’s latest forecast, the geomagnetic storm is expected to peak between 5 AM and 11 AM EDT (2 AM to 8 AM PDT). A moderate (G2) storm is projected to continue through the day, potentially lasting until 11 PM EDT (8 PM PDT).

If this timing holds, the best chances to witness the northern lights would be in Western Canada during the early morning hours on Monday, when the storm is at its peak. Unfortunately, for those in Ontario and Quebec, the storm may hit after sunrise, reducing the likelihood of a good aurora display.

That said, if the CME arrives later in the day, it could extend the storm into Monday night, offering a better chance for Eastern Canada to catch the auroras, assuming clear skies.

IMAGE FROM WeatherBell

Speaking of skies, Monday night’s cloud forecast looks promising for much of Canada. The latest model shows most areas should have a good view, with only Southeastern Manitoba, Northwestern Ontario, and Northern Quebec facing potential cloud cover that might obscure the show.

Southern Saskatchewan and Northern Alberta may see patchy clouds but could have breaks offering decent aurora visibility. For Southern Ontario, Quebec, and most of Western Canada, skies are expected to remain clear.

Check out our free app, Instant Weather for a more in-depth cloud coverage forecast specific to your exact location.

Another potential issue will be the full moon leading to the possibility of the northern lights appearing more dim and harder to spot. However, if the storm is as strong as forecasted, there still should be some chance to capture the show despite the bright moon.

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Northern regions of Canada, especially Northern Quebec, the Prairies and British Columbia, are almost guaranteed to see the northern lights, except for areas in Southwestern BC near Vancouver where visibility is less certain.

Zooming into more southern regions, the likelihood of seeing auroras becomes more variable. Northeastern Ontario, including Sault Ste. Marie, Sudbury, and North Bay, along with Western and Northern Quebec, have a strong chance of aurora sightings.

In Central Ontario, places like Muskoka, Algonquin Park, Bancroft, and the Ottawa Valley also have a moderate chance, as do areas around Montreal. However, the timing of the storm’s arrival remains a key factor—if it’s delayed and peaks closer to sunset, a G3 storm would likely provide an opportunity for these regions to witness the lights.

In Southwestern Ontario, the Golden Horseshoe, and southern Quebec near the American border, the probability becomes more uncertain. There’s a low to slight chance of auroras being visible here, depending on whether the storm overperforms or peaks later in the night.

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It’s important to keep in mind that light pollution can drastically affect your ability to see the northern lights. Urban areas, in particular, can drown out the skies, so you’ll need to find a dark spot away from city lights for the best chance to see the show. A resource like DarkSiteFinder can help you locate areas with low light pollution for optimal aurora viewing.

Northern Lights Timing

Many are accustomed to the precise scheduling of weather events, from thunderstorms and winter weather to solar eclipses, where timing is crucial. It’s understandable, then, that there’s a desire for a similar pinpoint timing for the best viewing of the aurora. However, the reality of predicting the best time to view the northern lights is not so straightforward.

Here’s the deal: Unlike weather events driven by terrestrial conditions, the aurora is influenced by solar activity, which is far less predictable. We can estimate that the northern lights are best viewed from just after sunset to just before sunrise, provided the skies are dark and clear. Beyond that, precise timing for peak aurora activity is challenging to forecast with current technology.

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Space weather forecasting doesn't yet allow us to predict exactly when solar energy will impact Earth. We know it's coming, but how and when it interacts with our planet's magnetic field can vary. Often, we only have a few hours' notice before the solar energy is detected by satellites.

Furthermore, the intensity of the northern lights can fluctuate significantly over short periods. You might have noticed this variance if you've observed the lights before—periods of dim activity suddenly bursting into vibrant colors. This is due to the variable concentration of solar particles interacting with our atmosphere.

While we can inform you a few hours ahead when conditions are likely to be good, predicting the exact peak of aurora activity is akin to forecasting the peak of a meteor shower; we know the best night but not the best hour.

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Smoky Skies Ahead as Upper-Level Wildfire Smoke Sets In Across Ontario

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Over the weekend, Ontario experienced an early taste of late fall weather, with flurries making an appearance in parts of Northern Ontario. Meanwhile, out west, temperatures have been heating up, fuelling a resurgence of wildfire activity.

Now, this same weather pattern has shifted into Ontario, bringing rising temperatures along with increased wildfire smoke from out west including fires in Saskatchewan and Alberta. With a stagnant air mass in place, the smoke is expected to linger over the next few days.

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The good news is that most of this smoke will remain high in the atmosphere, resulting in limited impacts on air quality. However, some minor smoke may reach the surface, which could affect those sensitive to air pollution. The most noticeable effect of the smoke will be at sunrise and sunset, creating a striking orange-red hue in the sky.

MODEL MAP FROM WEATHERBELL

We began seeing smoke move into the region late Wednesday, and it’s expected to thicken overnight into Thursday. By sunrise, two pockets of heavy smoke are forecast over Southern and Northwestern Ontario.

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Throughout Thursday, the smoke will continue to blanket the skies, with the densest areas concentrated over Northern, Central and Eastern Ontario. Expect a stunning sunset on Thursday evening—perfect for photography!

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MODEL MAP FROM WEATHERBELL

By Friday morning, the air mass will begin to shift westward, gradually clearing the smoke near the Manitoba border. However, Northeastern and Southern Ontario will likely remain under smoky conditions through Friday.

The heaviest smoke on Friday is expected along the Lake Superior and Georgian Bay shorelines.

Aside from the smoke, conditions will be ideal for this time of year, with above-average temperatures settling in across Ontario. This warm trend is expected to continue in the short term, with mild temperatures forecast into next week.

Snowy Surprise: Parts of Ontario & Quebec Could See Season’s First Snowflakes This Weekend

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As we enter the first full weekend of meteorological fall, Mother Nature is set to deliver a taste of autumn across Ontario and Quebec. A brief blast of cold air will cause temperatures to drop near the freezing mark during the pre-dawn hours on Saturday and Sunday.

Precipitation currently affecting Southern Ontario is expected to linger throughout the weekend. The heaviest rainfall totals are expected overnight Friday into early Saturday in Eastern Ontario, with localized amounts of 20-40 mm of rain possible.

The bigger story is when that precipitation wraps around into Western Quebec and Northeastern Ontario later on Saturday, continuing into the early morning hours of Sunday. With temperatures cooling into the low single digits and even colder air aloft, some of that precipitation may fall as wet snow.

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It appears that locations like Timmins, Cochrane, Kirkland Lake, Temiskaming Shores, Deep River, and Algonquin Park in Ontario could see their first snowflakes of the season. In Quebec, areas such as Ville-Marie, Rouyn-Noranda, Amos, and Val-d'Or may also experience wet snow.

While it's unlikely that snow will accumulate, as it will be mixed with rain and ground surfaces are still too warm, there's a chance that colder-than-expected conditions could lead to a few slushy centimetres in some areas. Any accumulation will melt quickly after sunrise on Sunday as temperatures gradually rise.

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Speaking of Sunday morning, this is when the coldest air of this brief "cold snap" is expected across Ontario and Quebec. Morning lows will likely drop into the single digits across much of Northern and Southern Ontario and Quebec. In Northeastern Ontario and the Algonquin Park region, temperatures could dip to near freezing during the pre-dawn hours, increasing the risk of frost in addition to the potential for wet snow.

Further south, the coldest temperatures in Southern Ontario will be in the higher elevations of Central Ontario, east of Muskoka, where temperatures may plunge to around 2-5°C. It will be moderately warmer in Southwestern Ontario, the Golden Horseshoe, and Eastern Ontario, with morning lows ranging from 5-10°C. Those along the shorelines of Lake Ontario, Lake Erie, Lake Huron, and Georgian Bay will benefit from the warmer lake waters, keeping temperatures above 10°C.

In Quebec, expect low to mid-single-digit temperatures in the western portion of the province near the Ontario border on Sunday morning. Eastern Quebec, including Montréal and Québec City, will see lows in the upper single digits, ranging from 6-12°C.

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WATERSPOUT RISK FOR GREAT LAKES ON SATURDAY MORNING (SORUCE: ICWR)

This cold air will also contribute to a potential waterspout outbreak over the Great Lakes this weekend. The highest risk is on Saturday, especially in the morning and afternoon, with a focus on Southern Lake Huron and Western Lake Erie. Waterspouts are also possible over Southern Georgian Bay, Western Lake Ontario, and even Lake Simcoe.

While waterspouts rarely threaten land, they can be hazardous for those on the water. In rare cases, waterspouts can come ashore, causing minor damage along the immediate shoreline.

The waterspout risk will persist into Sunday, with a focus on Eastern Lake Ontario.

Looking ahead to next week, warmer weather is expected to return to Ontario and Quebec. By late in the week, temperatures could climb back near the 30°C mark in Southern Ontario. So, while this brief taste of fall may be shocking, it looks like summer isn't quite finished yet.

Stormy Start to Long Weekend in Southern Ontario With Potential Severe Risk on Friday

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As we kick off the Labour Day long weekend, traditionally seen as the unofficial end of summer in Southern Ontario, we're keeping an eye on the potential for some active weather on Friday.

Friday is likely to be the warmest day of the long weekend, with temperatures soaring into the mid to high 20s during the afternoon, and the humidex making it feel into the 30s. The only exception is Eastern Ontario, where daytime highs will peak in the low to mid 20s.

This warm air will fuel thunderstorms expected to develop later in the afternoon and continue into the evening hours. The main risk zone covers Southwestern Ontario along the Lake Huron shoreline, but parts of the Golden Horseshoe and Central Ontario could also see some severe storms.

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Based on the latest model data, instability will increase throughout the afternoon as daytime heating builds energy in the atmosphere. Earlier data suggested that storm development might be delayed until late evening or even overnight, which would significantly reduce the available environment to fuel these storms.

However, the newest model data shows storm development occurring much earlier, as soon as 4-5 PM—right during the prime time when conditions are most favorable. Most models agree on storms developing over Lake Huron in the late afternoon, then moving ashore between Owen Sound and Goderich. Initially, storms are likely to be isolated but could merge into a cluster as they track eastward through Grey and Bruce counties along the southern shoreline of Georgian Bay.

Additional storm development is possible to the southwest around Windsor, Sarnia, Grand Bend, and London, where the environment is actually stronger than in the north. Although there's lower confidence in storm development here, any storms that do form could become quite severe, with all hazards on the table, including a risk of an isolated tornado.

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Looking towards the evening, the earlier cluster of storms is expected to reach the Lake Simcoe region by early evening. By this time, the storms will likely have lost some intensity but could still pose a marginal wind damage risk through the northern GTA and parts of Central Ontario, including Simcoe County, Muskoka, and the Kawartha Lakes region.

Storms are likely to linger into the early overnight hours across Southwestern Ontario and the Golden Horseshoe. There are indications of a flooding risk, with storms ‘training’—where multiple storms move over the same area like a train—leading to significant rainfall amounts. It’s unclear exactly where these storms might set up, but if they occur over urban areas that are more prone to flash flooding, significant flooding could occur overnight on Friday.

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Currently, we’re going with a ‘slight’ (level 2/5) risk for severe storms in Southwestern Ontario on Friday. This is driven by the potential for fairly widespread damaging wind gusts. Hail up to the size of quarters and an isolated tornado risk are also possible hazards. We may need to introduce a more targeted ‘strong’ (level 3/5) risk zone in an updated forecast if confidence increases in where the storms will develop.

For those in Central Ontario and around the Golden Horseshoe, we’re assigning a ‘marginal’ (level 1/5) risk, mainly due to the potential for 90 km/h wind gusts later in the evening, along with flash flooding from multiple rounds of storms. While the tornado risk isn’t zero, it will be less of a concern by the time the storms reach these areas.

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Summer’s Last Hurrah as Heat Returns to Southern Ontario & Conditional Strong Severe Threat on Tuesday

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Ready or not, the end of summer is rapidly approaching, with just one week left before students head back to school. Signs of autumn are already peeking through, with Environment Canada issuing a frost advisory last week in Northern Ontario, and of course, the arrival of pumpkin spice latte season!

However, it seems that Mother Nature has decided to give us one last taste of mid-summer weather. The start of this final week has brought steamy conditions, with warmer air making it feel like the 30s or even low 40s in some areas thanks to the humidex.

Along with the return of hot temperatures, we can expect some active weather, with multiple rounds of thunderstorms likely on Tuesday, possibly extending into Wednesday. While there is some uncertainty regarding the exact strength and timing of these storms, there is a risk that some could reach severe levels, bringing damaging wind gusts, large hail, and the potential for one or two tornadoes.

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As mentioned, the dynamics of Tuesday’s storm risk remain highly conditional on timing. Some models suggest that decaying thunderstorm activity from Michigan could track into Southwestern and Central Ontario during the morning hours. If this occurs, it could deplete the atmospheric energy needed for storms later in the day when conditions are more favourable.

It's important to highlight that the potential for a "bust" in this event is moderately high, which is why we're focusing on the overall storm threat based on the environment, should storms develop.

The strongest conditions are expected along the southeastern shoreline of Lake Huron, extending into Deep Southwestern Ontario during the afternoon and evening hours. Storms could begin developing anytime between 12-1 PM and continue until sunset around 8 PM.

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There is higher confidence in storm development further northeast around Lake Simcoe and into Central Ontario, though the environment isn't as strong in these areas. Multiple rounds of thunderstorms throughout the afternoon and early evening could impact the North Bay, Muskoka, Parry Sound, and Algonquin Park regions, with flash flooding being the primary concern.

In addition to the daytime storm risk, there are indications of a nocturnal storm risk around midnight, continuing into the pre-dawn hours of Wednesday. A strong line of storms could form over Michigan or Lake Huron and track across Southern Ontario. However, this will depend on earlier storms and how much energy remains in the atmosphere.

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Regarding expected storm hazards, we're assigning a 'strong' risk (level 3 out of 5) for parts of Southwestern Ontario, including Windsor, Chatham, Sarnia, Grand Bend, and London, based on the potential for widespread wind damage—again, this is conditional on storm development. Large hail up to the size of toonies and one or two tornadoes are also possible threats.

There is a widespread 'slight' risk for the rest of Southwestern Ontario and into Central Ontario. All storm hazards are possible, including strong wind gusts, large hail, and an isolated tornado. As mentioned, storms in Central Ontario could bring a flash flooding threat, with rainfall totals potentially reaching 100 to 150mm in the hardest-hit locations.

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Further east, the Golden Horseshoe and a portion of Eastern Ontario are under a 'marginal' risk, where some storms later in the day or overnight could approach severe limits, primarily due to strong wind gusts and hail up to the size of quarters.

Wet & Unsettled Weekend Brings Threat of Severe Storms and Significant Rainfall to Southern Ontario

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As we approach the final weeks of summer, with the back-to-school season around the corner and the arrival of astronomical autumn just under a month away, it seems Mother Nature is continuing the trend of a wet summer. The upcoming weekend is set to bring multiple rounds of rainy weather, and by early next week, we might even get a taste of early fall-like conditions, with possible single-digit lows for parts of Southern Ontario.

Rain over the next few days will come in waves, starting Friday afternoon in Southwestern Ontario and lingering through the weekend. Thunderstorm activity will play a significant role in this weekend’s rainfall, potentially leading to localized totals approaching 80mm. The rain should taper off by early Monday, with Eastern Ontario seeing the last of the precipitation.

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MODEL IMAGE FROM WEATHERBELL

As of Friday afternoon, the first wave of rain is already moving into Southwestern Ontario, extending into regions around Lake Huron and Georgian Bay. This cluster of rain and embedded thunderstorms is expected to gradually track eastward into the Golden Horseshoe and Central Ontario by Friday evening.

Rainfall amounts will be highly variable due to the thunderstorm component, but widespread totals of 5-15mm are expected by Saturday morning. Localized amounts could reach 25-50mm for areas that experience thunderstorm activity, though it’s difficult to pinpoint exactly where this will occur.

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Moving into Saturday, the rain will become less widespread, with a focus on Eastern Ontario and Southwestern Ontario during the morning hours. Eastern Ontario is expected to see lingering precipitation from Friday night’s first wave of rain.

We are also closely monitoring the risk of pop-up thunderstorms in Southwestern Ontario, extending into the Golden Horseshoe through late morning and early afternoon on Saturday. While these storms are expected to be mostly non-severe and primarily a rainfall risk, we can’t rule out a marginal severe threat, as the environment could potentially support some hazards, including hail and damaging wind gusts. An isolated tornado can’t be ruled out, though the risk is relatively low.

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MODEL IMAGE FROM WEATHERBELL

More isolated pop-up thunderstorms are expected across Southwestern Ontario, the Golden Horseshoe, and Central Ontario throughout Saturday afternoon and evening. There is concern that these storms will be slow-moving, with some areas experiencing multiple rounds of storms in a short time frame. This could lead to a heightened flash flooding risk, particularly in more urban parts of Southern Ontario, such as the Greater Toronto Area.

Due to the localized nature of the rain on Saturday, some areas may not see a drop, while others could receive upwards of 50-75mm of rain. The heaviest rain appears to be concentrated along the Hwy 401 corridor between London and Toronto, with other pockets of heavy rain in Central Ontario. However, this is just a general idea from one model and could shift depending on where the storms develop.

There should be a break in the rainfall overnight Saturday for most areas, although a few localized showers are possible, particularly around Southwestern Ontario and the Golden Horseshoe.

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MODEL IMAGE FROM WEATHERBELL

Similar to Saturday, pop-up thunderstorms are expected to return across Southern Ontario on Sunday morning and continue throughout the afternoon. These storms could bring additional heavy rainfall to the same regions affected by Saturday’s storms. Again, actual rainfall totals will vary significantly depending on where the storms hit, but some areas could see another 25-50mm (or more) by the end of Sunday.

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We are also closely monitoring the risk of severe storms in Eastern Ontario later in the afternoon and early evening on Sunday. Storms that develop here could bring damaging wind gusts, large hail, and potentially an isolated tornado. It’s still two days away, so much can change, but it appears that the Ottawa Valley, extending along the international border in Eastern Ontario, could see some marginally severe storms.

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Rain is expected to continue overnight into Monday morning for Central and Eastern Ontario, with pockets of heavy rain and embedded thunderstorms. Southwestern Ontario and the Golden Horseshoe should finally see the rain taper off by late Sunday evening, with the rain ending in Eastern Ontario sometime Monday morning. This will give way to clear conditions for Monday afternoon and evening.

However, the calm weather will bring much colder air, with overnight temperatures plummeting into the single digits across much of Southern Ontario on Monday and Tuesday nights. Daytime highs will struggle to reach the 20°C mark on Tuesday and Wednesday, making for a much cooler week compared to what we’ve experienced this summer.

Debby to Bring Flooding Threat to Parts of Southern Ontario on Friday With Up to 50-100mm of Rain Possible

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After making landfall in Florida earlier this week, what was Tropical Storm Debby has brought significant rainfall along the US East Coast. Now a post-tropical system, Southern Ontario is on track to feel the effects of the remnants of Debby over the next few days.

Significant rainfall is in the forecast with a particular focus on Eastern Ontario, which could see up to 100mm by the end of the week. This is not what many across Southern Ontario will want to hear, considering this year's unusually wet summer.

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There is still some uncertainty about the exact track of the system, as it won’t arrive until Friday. A more eastern track would shift the heavier rain across the border into the Northeastern US and Quebec.

On the other hand, if the system tracks further to the west, we could be talking about more widespread significant rainfall totals, potentially extending into Central Ontario and the Golden Horseshoe. Hence, it’s important to note that the forecast may change as we get closer to the arrival of the system.

MODEL IMAGE FROM WEATHERBELL

At this point, we are expecting to see some isolated pop-up showers and non-severe thunderstorms develop throughout the day on Thursday across Southern Ontario. This is in advance of the system on Friday, which is when we expect the bulk of the rainfall to occur.

Due to the localized nature of these storms, the rainfall totals will be extremely variable, ranging from a few millimetres to up to 15-20mm in the heaviest pockets by the end of Thursday.

MODEL IMAGE FROM WEATHERBELL

One thing we are closely monitoring is the potential for a persistent band of precipitation with embedded thunderstorms to develop late Thursday and carry into Friday. Current data suggests it will set up somewhere around Woodstock/Kitchener, stretching across Lake Simcoe and into Central Ontario.

This line could produce locally significant rainfall totals overnight and Friday morning as it essentially locks in place as the remnants of Debby approach from the southeast. Keep in mind that this line could shift and will be extremely localized, so not everyone will see the heavy rain. Local rainfall totals could approach 25-50mm by Friday morning, perhaps even higher if a particular area sees multiple rounds of thunderstorms.

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The precipitation associated with the system is expected to spread across Eastern Ontario by Friday morning, which is when we expect to see the bulk of the forecasted rainfall. This will only heighten the flooding threat since it will all happen within the span of a few hours.

In addition to the rain, we are also likely to see some embedded thunderstorm activity within the bands of precipitation throughout the morning and afternoon on Friday.

These storms should stay mostly non-severe, but we’ve seen in the past that these tropical systems have a tendency to present a tornado threat, especially along the western side of the system, which is where Southern Ontario will be positioned.

This is certainly not a guarantee for tornadoes, but we will be closely watching this aspect of the system and will issue a more detailed forecast if it becomes more likely.

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MODEL IMAGE FROM WEATHERBELL

Rain is expected to taper off in the west through Central Ontario into the Golden Horseshoe by early afternoon on Friday. For Eastern Ontario, heavy rain is expected to continue throughout the afternoon and early evening hours on Friday.

We should begin to see some clearing in the west by dinner time, with the rain finally coming to an end around midnight for the Ottawa Valley and those along the St. Lawrence.

As we’ve mentioned, the highest impact of this system is expected in Eastern Ontario, which will be closest to the track of the system. Rainfall totals are likely to generally range from 50-100mm, but some localized pockets could even exceed the 100mm mark based on some of the latest model data.

It is important to keep in mind that thunderstorm activity will play a big role in the rainfall totals, so the actual totals could vary significantly between locations. That’s why we have a large range of 50mm - it’s hard to nail down the exact totals due to the localized nature of thunderstorms.

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The forecasted rainfall totals drop off quite fast once you head further west. We are projecting between 25 to 50mm of rain for the Golden Horseshoe and parts of Central Ontario around Lake Simcoe.

At this point, we are expecting 15-30mm of rain for the Greater Toronto Area (GTA) along the Lake Ontario shoreline into the Niagara region. That could change if that line of rain overnight Thursday shifts into the GTA, as the latest models suggest should develop just to the northwest.

Less than 20mm of rain is expected for Southwestern Ontario, with even lower totals for Deep Southwestern Ontario, which may see barely a drop of rain from this system.

Mid-Week Strong Severe Risk for Southern Ontario on Wednesday; Tornadoes Possible in the Ottawa Valley

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It has been a relatively quiet month for severe weather across Southern Ontario, aside from the significant rain that caused flash flooding in parts of the Greater Toronto Area last week. To put it into perspective, we have only seen two confirmed tornadoes this month, both occurring on July 10th in London.

However, the quiet period might be coming to an end with a potent storm threat for parts of Central and Eastern Ontario on Wednesday. All severe hazards are possible, including large hail, damaging wind gusts, and maybe even one or two tornadoes.

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The storm threat will kick off quite early, with developing storms over Georgian Bay during the mid to late morning hours on Wednesday. Based on the latest models, these storms are likely to track into regions east of Georgian Bay, such as Parry Sound, Muskoka, and Simcoe County, between 10 AM and 1 PM. They could present some marginal severe threats, including strong wind gusts and hail up to the size of quarters. An isolated tornado can’t be ruled out.

By early afternoon, we expect these morning storms to begin merging into one main cluster of storms somewhere around Lake Simcoe. This cluster will be tracking into a more established environment through Bancroft and extending into the Ottawa Valley. As a result, the storm will likely intensify throughout the early to mid-afternoon hours.

There is some disagreement on the exact placement of this storm, but almost all models agree on the intensity. This is where we believe the tornado threat is the strongest.

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Further storm development is possible to the southwest of the cluster, extending through Peterborough into parts of the Greater Toronto Area during the afternoon hours. These storms will gradually track to the east or northeast, although they could move quite slowly, leading to a potential flash flooding threat. Hail and strong wind gusts are also possible. An isolated tornado can’t be ruled out.

The storm risk will come to an end by early evening for those around Lake Simcoe and the Greater Toronto Area. For Eastern Ontario and the Ottawa Valley, expect the storms to fizzle out around 9 to 10 PM.

The focus of this severe risk will be on the Ottawa Valley, including Bancroft, Barry’s Bay, Smiths Falls, Renfrew, and the City of Ottawa. This is where we have a 'strong' (level 3) severe risk driven by the potential for large hail up to the size of golf balls. One or two tornadoes and damaging wind gusts are also possible with any storms that develop in this area.

The rest of Eastern Ontario, including Brockville, Kingston, Peterborough, and regions around Lake Simcoe, have a 'slight' (level 2) severe risk. Hail up to the size of toonies, damaging wind gusts, and heavy rainfall are possible threats. An isolated tornado is possible, but the strongest tornado risk should be contained to the Ottawa Valley.

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For regions east of Georgian Bay into the Greater Toronto Area, there is a 'marginal' (level 1) severe risk. We don’t expect widespread severe weather here, but a few storms could bring isolated strong wind gusts and quarter-sized hail.

We will be closely following this threat and will post an updated forecast if there are any significant changes in the model data.

Early Morning Strong Severe Risk Followed by Widespread Threat Later in Day on Monday for Southern Ontario

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A complex weather situation is set to unfold across Southern Ontario over the next 24 hours as heat-fueled severe threats bring multiple rounds of storms on Monday.

We are already seeing the formation of what will be the first round of storms, expected to track into Southwestern Ontario early Monday morning. A cluster of intense storms began taking shape over Wisconsin and Illinois late Sunday evening. The Chicago area took a direct hit, prompting a tornado warning to be issued with multiple visible areas of rotation on radar over the city.

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The environment is building ahead of the storms, and models agree that it will maintain its strength through the overnight hours as it tracks eastward through Michigan. Based on this, we feel that the Windsor and Chatham areas could face a strong risk of severe weather starting around 4-5 a.m. on Monday. The exact arrival of this storm and its strength remain somewhat uncertain.

The main concern is the potential for destructive wind gusts exceeding 100 km/h. As seen in Chicago, brief spin-ups aren’t out of the question, so an isolated tornado threat could also be present. The hail risk will be lower, likely maxing out at around nickel to quarter-sized hail.

The first round of storms will come to an end by the late morning hours as the decaying line of storms moves out over Lake Erie and south of the border. However, this won’t be the end of the risk for Monday. Additional storms could follow in the wake of that main line through Southwestern Ontario around the noon hour.

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A more widespread threat of severe weather is expected to develop during the early afternoon hours in the Niagara region and to the northeast of Lake Simcoe. All severe hazards could be on the table, including hail up to the size of toonies, damaging wind gusts, and an isolated tornado.

Starting with the Niagara region, the latest model data shows the development of a cluster of strong storms somewhere around London and Brantford during the early afternoon. The environment is favourable for this cluster to become severe as it tracks along the Lake Erie shoreline into the Niagara region and crosses the border into New York by the mid to late afternoon.

Further north, storms are likely to bubble up along a corridor stretching from Lake Simcoe through Bancroft and into the Ottawa Valley starting around 2 to 4 p.m. and continuing into the early evening hours. This activity is expected to be fairly isolated, and not everyone will see a storm, but the potential is there for anywhere in Central and Eastern Ontario.

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We have opted for a ‘strong’ (level 3 out of 5) severe risk for Deep Southwestern Ontario, including Windsor and Chatham. This is driven by the destructive wind gust threat early Monday morning with the expected line of storms around 4 to 6 a.m.

Outside of the strong risk, we have a ‘slight’ (level 2) severe risk for the Niagara region along with parts of Central and Eastern Ontario. A few storms could reach the severe threshold with toonie-sized hail, damaging wind gusts, and an isolated tornado.

The rest of Southern Ontario is in the ‘marginal’ (level 1) severe risk, as it can’t be ruled out that any storms that pop up could present some severe hazards. It’s important to note that it’s hard to pinpoint where these storms will appear, so you are not guaranteed a storm even if you are in a risk zone on our map.

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We have our eyes on Tuesday, which could see a fairly strong risk of severe storms during the afternoon and evening hours. At this point, Central and Eastern Ontario appear to be in the bullseye for a second day, with the threat likely ranging from a ‘slight’ (level 2) to a ‘strong’ (level 3) risk. This could also extend into parts of the Golden Horseshoe. A more detailed forecast for Tuesday will be issued by late Monday.

Isolated Severe Threat to Cap Off the Weekend for Parts of Southern Ontario on Sunday

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Many across Southern Ontario enjoyed a beautiful start to the weekend on Saturday, with temperatures soaring into the upper 20s and even low 30s. This prompted Environment Canada to issue heat warnings in some parts of Southern and Northern Ontario, as this prolonged period of hot weather is expected to continue into the upcoming week.

As is typical, the hot temperatures are expected to fuel several rounds of potential severe weather over the next few days. This will begin on Sunday with an isolated severe risk for parts of Southwestern and Central Ontario, along with the Greater Toronto Area.

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Current data suggests that there could be two separate rounds of storms on Sunday. The first round could lead to a noisy wake-up call during the morning hours as a decaying line of storms crosses over Lake Huron into Southwestern Ontario from Michigan.

We expect that the line will reach our region sometime between 8 and 10 a.m. However, there is some disagreement among the models on how strong this line will be by the time it crosses the border.

If it doesn’t fizzle out before reaching our region, it could feature marginally severe wind gusts ranging from 90 to 100 km/h along the Lake Huron shoreline and into Deep Southwestern Ontario. The tornado threat is fairly low due to the timing and storm mode, but as always, it can’t be fully ruled out.

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This first round will be critical in setting the stage for the second round of storms later in the day during the afternoon. If the morning storms take longer than expected to clear out and linger into the early afternoon, this may prevent the daylight heating needed for further storm development.

Provided that the morning storms move out in a timely fashion, we expect isolated storms to pop up anywhere from Lake Huron extending to the northeast into areas around Lake Simcoe and parts of Central Ontario. This could begin as early as 2-3 p.m. with storm development possible through the early evening hours.

Due to the lower confidence in storm development, we are currently forecasting a marginal (level 1) severe risk. Any storms that do develop could present all severe hazards, including damaging wind gusts, large hail up to the size of quarters, and maybe even an isolated tornado.

We may need to consider an upgrade to a slight (level 2) risk in an updated forecast once we see how fast the morning storms clear out and allow for further daylight heating.

The storm threat will come to an end by the late evening hours on Sunday once the sun goes down. We are closely watching the potential for more storms on Monday; however, at this point, the threat is looking extremely isolated with limited storm development. Tuesday is looking a lot more active in terms of storms.