Warm Temperatures Briefly Return With Isolated Severe Thunderstorm Risk for Southern Ontario Wednesday

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While much of late May across Southern Ontario was dominated by unseasonably cool weather, the start of June is shaping up to be a very different story. Over the past few days, temperatures have rebounded to near-seasonal levels across the region, and that’s just a preview of what’s ahead. But enjoy it while you can because a noticeable cool down is expected later this week.

This early June heat has also arrived with a layer of upper-level smoke drifting in from wildfires burning across Western Canada. This smoke has caused a light haze in the sky, giving the air a faint smoky smell, dimming the sun, and slightly suppressing daytime temperatures compared to what we would have seen under clear skies.

The good news is that much of this smoke is expected to clear out across Southern Ontario overnight into early Wednesday morning. While some lingering smoke may remain high up in the atmosphere, it shouldn’t be as thick or widespread as what we’ve seen over the past 36 hours.

With clearer skies, daytime heating will be more effective, giving temperatures a better shot at reaching their full potential. On Wednesday, we’re expecting highs to climb into the upper 20s and possibly even low 30s in some spots.

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A cold front sweeping across the province late Wednesday will bring a shift in the pattern, knocking temperatures back below seasonal for the latter half of the week. This front is also expected to trigger a line of thunderstorms, some of which may be marginally severe.

Primary threats include damaging wind gusts up to 90 km/h, pockets of quarter-sized hail, and localized flooding from slow-moving storms. There is also a very low risk of an isolated tornado, but given the weak storm environment, this threat is quite uncertain and likely limited.

ESTIMATED AIR TEMPERATURE - MAP FROM WEATHERBELL

Much of Wednesday will start off hot and hazy, especially across Southern Ontario. Temperatures will rapidly climb into the upper 20s by early afternoon ahead of the approaching cold front. In some areas, particularly Deep Southwestern Ontario, the Golden Horseshoe, and the Ottawa Valley, temperatures could push into the low 30s.

That said, locations along the immediate shorelines of the Great Lakes will likely remain a few degrees cooler due to the lake breeze. These areas, including communities along Lake Erie, Lake Ontario, Lake Huron, and Georgian Bay, should see highs closer to the low to mid-20s.

As the cold front begins moving in from the northwest, starting around 2 to 4 PM near the Bruce Peninsula and the North Bay and Parry Sound region, we’ll see an almost instant temperature drop. It could fall by as much as 10 to 15 degrees within a couple of hours. The front will then gradually push southeast through the rest of the afternoon and into the early evening hours.

As the temperatures rise, it’s crucial to keep our beloved pets safe and comfortable. Here are some essential tips to ensure your furry friends stay cool this summer:

🚗 Never Leave in Cars: Even with windows cracked, the temperature inside a car can rise dramatically in just a few minutes. On a 24°C day, the temperature inside a parked car can soar to 38°C in just 10 minutes. In 30 minutes, it can reach 49°C! Leaving your pet in a car can be deadly, so never leave them unattended.

If you see a pet left unattended in a car in Ontario:

  • Look for the Owner: Note the car's make, model, and license plate number. Go to nearby businesses to see if you can find the owner.

  • Call for Help: If you cannot find the owner, call your local animal control or police. You can call the OSPCA at 1-833-9-ANIMAL (264625). If you believe the animal is in immediate distress, call 911 immediately.

  • Stay with the Pet: Remain with the pet until help arrives.

🏡 Shade & Shelter: Make sure your pets have access to shaded areas to avoid direct sunlight. A cool, sheltered spot can make a big difference.

💧 Hydration is Key: Always provide fresh water for your pets. Dehydration can set in quickly, so keep their water bowl filled and in a shaded area.

🐕 Limit Exercise: Avoid walking your pets during the hottest parts of the day. Early morning or late evening walks are best to prevent overheating.

🐾 Paw Protection: Hot pavement can burn your pet's paws. Walk them on grass whenever possible, or use protective booties to shield their feet.

⚠️ Watch for Signs of Overheating: Symptoms include excessive panting, drooling, and lethargy. If you notice these signs, move your pet to a cooler area immediately and provide water.

UPPER LEVEL SMOKE CONCENTRATION - MAP FROM WEATHERBELL

Although the smoke won’t be nearly as thick as what we experienced Monday and Tuesday, some light to moderate upper-level smoke may still linger on Wednesday. Forecast models suggest the highest concentrations will likely be around the Golden Horseshoe, including the Greater Toronto Area, Hamilton, and the Niagara region.

There may still be a faint smoky smell in the air at times, but surface-level smoke isn’t expected to be heavy enough to significantly impact air quality. What it could do, however, is hold temperatures back by a couple of degrees in some spots since the sunlight won’t be able to fully break through the smoke layer.

By Thursday, most of this smoke should clear out completely. That said, some models are hinting at another round of wildfire smoke pushing into the region by late this week or into the weekend.

SIMULATED RADAR - MAP FROM WEATHERBELL

Along with cooler temperatures, the advancing cold front will bring the potential for thunderstorms across Southern Ontario. Current data suggests that a line of storms will begin forming early Wednesday afternoon, stretching from North Bay down into parts of Michigan.

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As this front continues to track southeastward, conditions will become more favourable for some of these storms to become locally severe. Isolated threats include damaging winds, large hail, and heavy downpours. The highest risk zone appears to be in a corridor running from Deep Southwestern Ontario through Kitchener and Waterloo, into the Lake Simcoe region, and extending northeast into the Algonquin Park area.

The timing for the strongest activity looks to fall between 3 PM and 6 PM, though it could stretch a bit later, especially in areas near the border. Some model runs even show a rogue thunderstorm crossing into the Windsor or Sarnia area from Michigan during the evening hours.

The overall tornado threat remains low due to the weak storm environment and expected messy storm mode, but it is never zero. Sometimes we do see surprise spin-up tornadoes in Ontario, especially where lake breezes collide and enhance low-level rotation.

After sunset, the severe risk should wind down fairly quickly. However, a few non-severe thunderstorms may continue into the late evening and overnight as the front moves across the Golden Horseshoe and into Eastern Ontario.

Slight Risk for Isolated Severe Thunderstorms on Thursday with 100km/h Wind Gusts, 3cm Hail & Isolated Flooding Possible

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We’re closely monitoring a slight risk for isolated severe thunderstorms this afternoon and evening in parts of central Alberta. Areas such as Edmonton, Edson, Red Deer, Whitecourt, Leduc, Camrose, Rocky Mountain House, Drayton Valley, High Prairie, Slave Lake, Lac la Biche, Westlock, Hinton, Olds and surrounding communities may see these storms. However, as they’ll be isolated, most areas will not receive any precipitation at all.

Damaging wind gusts of 80-100km/h, 3cm hail and isolated flooding up to 50mm are the main risks for these storms. Of course, frequent lightning and torrential rain are also expected for those who are affected by these storms.

The overall tornado risk is low so chances of a spin-up are unlikely. However, we all know that stranger things have happen so definitely make sure to have our free app Instant Weather to get notified of any and all alerts from Environment Canada for your area.

Environment Canada has also issued Severe Thunderstorm Watches for the region, shown below.

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Environment Canada writes:

”Conditions are favourable for the development of severe thunderstorms this afternoon and evening that may be capable of producing strong wind gusts and large hail.

Damage to roofs, fences, branches or soft shelters is possible. When thunder roars, go indoors! Lightning kills and injures canadians every year.

Severe thunderstorm watches are issued when conditions are favourable for the development of thunderstorms capable of producing damaging hail, wind or rain.”

In addition to the severe thunderstorm risk, the Fire Danger map for Alberta shown below is very concerning as almost all areas of Alberta are under “Extreme” fire danger.

Fire danger map for may 29th produced by the government of Alberta

With the expected lightning, warmer temperatures and drier conditions, it’s very possible we could see new wildfires ignited from these storms today. Please stay safe folks and we’ll post more updates when available.

Slight Risk for Severe Thunderstorms on Monday as a Cold Front Advances Through Alberta

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The past week was fairly quiet, as far as active weather is concerned, with the odd pop-up thunderstorm surpassing the severe threshold and a couple of funnel cloud reports. This week, however, is slated to start off with a bang as a cold front will move into Alberta later this afternoon, stretching the length of the province and triggering the development of thunderstorms over a widespread area.

We’ve already seen some scattered showers across parts of Central and Northern Alberta today, but the severe threat won’t begin until this afternoon, around 2-4pm. These will be fast-moving storms that will quickly develop and organize into a north-south line along the cold front as it crosses the province through the afternoon and evening. Storm activity will rapidly diminish as we get later into the evening, but isolated storms could continue until closer to midnight, if conditions remain favourable.

The greatest thunderstorm risk will stretch from Calgary northward up to Fort McMurray, highlighted in yellow on our map. This large region could see damaging wind gusts of up to 100km/h and large nickel to quarter-sized hail, along with torrential downpours. At this point, the threat of a tornado appears to be unlikely, but it can not be completely ruled out.

Fire danger map for may 26th produced by the government of Alberta

The amount of lightning associated with today’s storms could also be a concern. Warmer temperatures and drier conditions have elevated the wildfire risk over the past week and has led to High to Extreme Wildfire Danger across the entire province. Significant amounts of lightning, despite the presence of precipitation, could easily spark additional fires given these conditions.

Nocturnal Thunderstorm Threat With Damaging Wind Gusts and Isolated Tornado Risk for Southwestern Ontario Tonight

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updated map - 10:50 PM (CLICK HERE FOR THE PREVIOUS MAP)

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UPDATE (10:50 PM):

We’ve been closely tracking the line of storms developing across Michigan, and it’s now set to move into Deep Southwestern Ontario over the next few hours.

Based on the latest model data, current environmental conditions, and how well the storm is holding together despite the lack of daylight heating, we believe there’s enough evidence to upgrade parts of Deep Southwestern Ontario to a ‘strong’ (3/5) risk—mainly due to the potential for intense wind gusts.

Large hail up to the size of toonies is also possible, and we can’t completely rule out an isolated tornado.

We’ve also extended the ‘slight’ (2/5) risk further inland to include areas like Goderich and London, as new data suggests the line could stay fairly strong as it tracks deeper into Southwestern Ontario during the pre-dawn hours. Again, damaging wind gusts remain the primary threat.

The line is expected to cross the border just after midnight, with the severe threat gradually tapering off but still continuing until around 3–4 AM.

ORIGINAL FORECAST

While storm season has had a quiet start in Southern Ontario, things are beginning to ramp up with a late-night storm risk expected between Thursday evening and early Friday morning. A strong line of storms is forecast to form across Michigan late tonight, initially beginning as discrete supercells over parts of Wisconsin and Illinois.

Based on the latest guidance, these storms are expected to organize into a more linear structure as they track eastward, eventually crossing into Southwestern Ontario sometime just after midnight. While they’ll likely lose some of their strength after dark, especially without daytime heating, the atmosphere may still be supportive enough for them to maintain some intensity as they move into our region.

That said, there’s still a fair amount of uncertainty about just how strong this line will be once it crosses the border, and how quickly it might weaken as it tracks northeast through the early morning hours of Friday.

The biggest concern with this system is the potential for damaging wind gusts. This squall line will stretch from the Upper Peninsula of Michigan all the way down through Ohio as it enters Ontario, which could lead to widespread impacts. Areas from the Bruce Peninsula all the way down to Deep Southwestern Ontario are at risk of strong winds embedded within the line.

The highest risk appears to be in Deep Southwestern Ontario, where the line will first cross into Ontario. Regions like Windsor, Leamington, Chatham, and Sarnia are most likely to experience the strongest part of this line. While damaging wind gusts are the main hazard, we also can’t completely rule out the chance for hail and even a brief tornado, especially if the storms arrive a bit earlier than forecast.

Hail up to the size of quarters is possible, and while the tornado risk is considered low overall, it does exist. The biggest concern here is that this is a nocturnal threat. If a tornado were to develop overnight, it would be harder to spot and could be rain-wrapped, making it even more dangerous. That’s why it’s so important to stay alert and have a way to receive warnings while you sleep.

SIMULATED RADAR - MAP FROM WEATHERBELL

Storm development will begin with discrete cells over Wisconsin and Illinois, likely forming into a long line around 8–10 PM near Chicago and across Lake Michigan.

The timing of this formation is crucial. If the line develops sooner and sweeps across Michigan quickly, it could result in a more robust severe risk for Deep Southwestern Ontario, where the environment is more favourable before midnight.

No matter the timing, damaging winds remain the most likely outcome with this type of linear storm setup.

SIMULATED RADAR - MAP FROM WEATHERBELL

As of now, future radar models suggest the storms will cross into Ontario between 1 and 2 AM, hitting areas like Windsor and Sarnia first before stretching further northeast. However, there’s still wiggle room in this timing. It could arrive earlier and stronger, or later and already weakening before reaching our region.

ESTIMATED TORNADO ENVIRONMENT - MAP FROM WEATHERBELL

While widespread wind damage is the primary concern tonight, there is some minor tornado potential—especially in Essex County just after midnight. Again, the odds are low, but not zero.

Because of the overnight timing, it's extra important to have notifications enabled on your phone or weather radio. Make sure you have a way to receive alerts while you're asleep in case a warning is issued. Our free app is a great way to instantly get Environment Canada alerts, along with our custom notifications issued for your exact location.

SIMULATED RADAR - MAP FROM WEATHERBELL

The line of storms is expected to continue northeast through the early morning hours, bringing heavy rain, gusty winds, and frequent lightning to much of Southwestern Ontario and parts of the Greater Toronto Area between 3 and 6 AM.

While the line should gradually weaken during this time, it could still pack a punch in some localized areas. There’s some uncertainty around how long it will be able to hold its strength since the atmospheric environment in Ontario is notably weaker than what the storms had access to in the U.S.

Latest model runs show the system likely fizzles out once it reaches Lake Simcoe, meaning Eastern and Central Ontario probably won’t see much beyond a few scattered morning showers or storms.

Another round of storms is possible Friday afternoon and evening, particularly for Eastern Ontario and parts of Deep Southwestern Ontario. We’ll have more details on that in a separate update.

As it stands, the highest storm risk tonight is in Deep Southwestern Ontario, where we currently have a slight risk (2/5) for severe weather. The main hazard is damaging wind gusts between 12 and 6 AM, though isolated tornadoes and hail up to the size of quarters are also possible.

For the rest of Southwestern Ontario and the Golden Horseshoe, the risk is lower—a marginal (1/5) severe threat—with isolated pockets of wind damage being the most likely outcome. There’s also a very low tornado risk along the Lake Huron shoreline as the line initially pushes into the region. Hail up to the size of nickels could accompany some of these storms.

In addition to the overnight threat, a few isolated pop-up storms are possible during the late afternoon and early evening across parts of Grey-Bruce. While these are not expected to be severe, funnel clouds are possible, including a low-end risk of a landspout tornado. See our custom notification for more on the funnel cloud setup.

Stay weather-aware tonight. Keep your devices charged, notifications turned on, and have a plan in place just in case you need to take shelter quickly. We’ll continue to monitor the latest data and provide updates as the situation evolves, including a possible live stream later tonight.

First Slight Severe Thunderstorm Risk of the Year for the Prairies Monday Afternoon Through Tuesday Morning

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While we saw some severe storms eventually develop in Southeast Saskatchewan and Southwest Manitoba yesterday, the severe threat for today and into the overnight hours is heightened, resulting in our first Slight Risk of the season.

We’ve already seen heavy rain falling in parts of Central and Southern Alberta today, but thunderstorms have begun to develop and will continue as we progress later through the afternoon and into the evening At this point, it’s possible that these storms may become severe, with the main threat being strong wind gusts and heavy rain. The environment today is also conducive for the development of landspout (non-supercell) tornadoes around Calgary and to the east of the city so we will be watching this situation closely.

It’s further east, in Southern and Central Saskatchewan and Manitoba, that we’re seeing the greatest severe thunderstorm threat. Isolated storms are expected to start developing in the early evening, around 5-6pm and possibly a bit sooner in the afternoon, and models are once again suggesting that the environment could be favourable for the development of supercells.

A bit later in the evening, closer to 7-8pm, we could see some additional storm development in Southwest Saskatchewan as a multicellular line. This complex of storms would travel northeastward across the province and move into Central Manitoba in the early morning hours of Tuesday. It’s during these early morning hours that we could also see more isolated storms develop in Southwest Manitoba.

Large hail, damaging winds, and torrential downpours are all concerns with today’s storms. The possibility of tornadoes is low, but the development of one or two can not be completely ruled out.

Marginal Risk for Thunderstorms in Southern Saskatchewan and Manitoba Beginning Sunday Evening

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With the arrival of the first heat wave of the year to Southern Saskatchewan and Manitoba this weekend, we’re also looking at our first real threat of severe thunderstorms for the season.

Isolated storms are expected to develop along the American border in both Saskatchewan and Manitoba this evening, starting around 5-7pm. The storms will travel northeastward into both provinces throughout the evening and into the overnight hours.

Models are suggesting that the environment could be favourable for the development of supercells, but further analysis puts the development of severe storms in question and storms could remain sub-severe. One particular area of interest for possible severe storm development will be in Southeastern Saskatchewan and through the Westman and Interlake Regions.

If severe storms end up developing this evening, the overall threats are expected to be limited. These storms could produce small hail and strong wind gusts, while the possibility of a tornado is unlikely.

First Strong Severe Thunderstorm Risk of the Season in Southern Ontario on Tuesday With Tornadoes Possible

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After a gruelling winter filled with relentless snow squalls, powerful winter storms, and a major ice storm to top it all off, we are finally shifting gears into more typical spring and summer-like weather across Southern Ontario. But with the warmer air comes the return of severe thunderstorms, something Southwestern Ontario has already gotten a small taste of over the past few weeks.

We have been closely tracking the potential for our first strong severe weather threat of the season on Tuesday. Model guidance has been consistently highlighting the potential for a very active environment, one capable of supporting tornadoes, large hail, and damaging wind gusts. That risk still looks to be on track, although there remains some disagreement between models on exactly where the strongest environment will set up.

At this time, we believe the strongest severe weather risk will focus across parts of Southwestern Ontario, Central Ontario, and into Eastern Ontario. Other areas across Southern Ontario will still carry a marginal to slight risk, meaning a few severe storms could pop up, but the widespread threat will be lower outside the main zone.

Tuesday’s possible storm threats include one or two tornadoes, large hail — potentially up to the size of toonies or even timbits — widespread damaging wind gusts over 90-100 km/h, and heavy rainfall that could cause localized flooding in some spots.

The storm risk will kick off early Tuesday morning as an area of convection moves across the region between 6:00 a.m. and 12:00 p.m. Most of these morning storms should remain non-severe, but we can't rule out a rogue severe cell, especially in setups like this. Where these morning storms track and how quickly they clear out will be important to watch, as leftover clouds or rain could limit how unstable the atmosphere becomes later in the day.

By the early afternoon hours, the environment is expected to rapidly become more favorable for severe weather. Areas along the Lake Huron shoreline will likely be the first to feel the effects, with the risk then spreading into parts of Central Ontario.

Even though we are confident that the setup is capable of producing severe storms, it’s important to stress that storms actually have to form to take advantage of the environment. Not everyone in the higher-risk zone will necessarily see a storm. These will be isolated events, meaning only a small percentage of the region will be directly impacted.

The highest tornado risk will likely occur earlier in the day across Southwestern and Central Ontario, when individual storms (known as discrete supercells) can remain separated and feed off the prime environment around them.

As the afternoon progresses and storms track further eastward, we expect that they will start to merge into more of a line, which would shift the threat more towards damaging winds and heavy rain rather than tornadoes and large hail.

By late afternoon into early evening, the severe weather risk will push eastward into the Golden Horseshoe and Eastern Ontario. The good news is that the risk should wind down quickly after sunset, which occurs around 8:00 p.m.

There could still be some leftover showers or weak storms lingering into the evening, especially across Eastern Ontario, but the threat for damaging weather will rapidly diminish once the sun goes down.

We’ll continue to monitor this setup closely and provide updates as new data becomes available. Stay tuned, and as always, make sure you have a way to receive alerts if storms develop in your area.

Download our free app to instantly get any Environment Canada alerts and our own custom notifications pushed to your phone. We are planning to go live to cover any storms that develop throughout the day on Tuesday. Please subscribe to our YouTube channel here so you can be notified when we go live.

REGIONAL BREAKDOWN

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.

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.

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.

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.

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.

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.

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.

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.

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.

Late Season Storms Bring a Slight Severe Risk for Southern Saskatchewan Tuesday Evening and Through Wednesday Morning

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As we continue later into September, it seems that summer is still hanging on, with some active weather this morning and into the afternoon and additional stronger severe storms beginning later this evening that will continue into Wednesday morning. The combined wind, hail, and tornado threat from the impending storms has resulted in a Slight Risk for a large portion of Southern Saskatchewan.

The storms will start to develop as individual cells along the border in the early to mid-evening in Southwest Saskatchewan. This will be followed by a line of storms from south of the border that will make their way northward into the province later in the evening and into the overnight hours. A final round of storms is expected to arrive a few hours later, spreading much further north into Central Saskatchewan and weakening later into the morning. Due to the positioning of the low pressure that these storms will the centred around, areas closer to the Alberta border could see steady moderate rainfall lasting throughout Wednesday afternoon and evening.

These storms are expected to produce hail that could be larger than a toonie, along with damaging wind gusts upwards of 100km/h, and the possibility of one or two tornadoes. There is also the concern of localized flooding, particularly further west, where the storms and the subsequent extended period of rainfall could bring up to 100mm of rain.

Slight Risk for Severe Thunderstorms in Southern Manitoba This Afternoon and Into Tuesday Morning

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Following some morning and early afternoon rain, Southern Manitoba can expect more active weather with severe thunderstorms beginning this afternoon and continuing into Tuesday morning. The possibility of large hail and flooding caused by heavy downpours make this a Slight Risk in Southeast and South-Central Manitoba.

The activity will begin this afternoon with a line of storms pushing northeastward into the region from North Dakota. Development of further storms will continue through the evening and into the pre-dawn hours of Tuesday, resulting in some locations seeing multiple rounds of thunderstorms. The storms that develop later into the evening could be more organized and are expected to be stronger that the afternoon storms.

These storms may bring some large hail, up to the size of a timbit, as well heavy rains that could result in areas of localized flooding. There will be some strong wind gusts that are expected to top out in the 90-100 km/h range and the possibility of an isolated tornado can not be completely ruled out.

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.

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.

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.

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.

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.

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.

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.

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.

Threat of Massive Hail is the Driving Force Behind a Widespread Strong Severe Risk in Southeast Manitoba Sunday Afternoon IF Storms Develop

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It’s been a very active few days across the Prairies and this morning was no exception, with destructive wind gusts pummelling parts of East Central Saskatchewan and the Westman and Parkland Regions.

Unfortunately, this trend of dangerous severe weather will likely continue this afternoon, but this time the target will be Southeastern Manitoba. The possibility for massive hail across the region has resulted in this being a widespread Strong Risk for severe thunderstorms for this afternoon.

Once again, weather models are struggling with pinpointing these storms, but the ingredients for severe weather should all be in place and there is a potential for severe storm development, which warrants a forecast. Today will be an “IF day” in the sense that IF storms end up developing, they are expected to be very strong and widespread across the region. With the intense heat and temperatures feeling into the low 40s, along with ample moisture and instability, the environment will be primed for storms, but a strong enough trigger will be necessary for them to occur.

This storm development could begin early this afternoon, as the existing line of storms pushes northeastward through the Interlake Region. Behind this, additional storms could develop along a cold front and make their way eastward through the Red River Valley and Interlake Region during the afternoon and the Eastman and North Eastman Regions in the evening and overnight hours. Whether or not this development actually occurs is still uncertain.

If the severe thunderstorms end up developing this afternoon, the major threat will be very large hail. Golf ball-sized hail appears to be likely with these potential storms, with even up to tennis ball-size possible. Widespread damaging wind gusts over 100km/h would also be associated with these storms, as well as up to 100mm of rain resulting in localized flooding and the possibility of a tornado.

This could very well end up being a bust, but the threats involved in the event that storms do develop are quite significant and it’s important to be prepared.

Strong Risk for Severe Thunderstorms in Southeast Saskatchewan This Evening and Through Sunday Morning

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Southeastern Saskatchewan is in the crosshairs for severe weather once again, with some storms firing up along the American border later this evening followed by another round of strong storms early Sunday morning. The hail, wind, and tornado risk between the evening and morning storms makes this a Strong Risk along the southern border and a Slight Risk stretching through Southeast Saskatchewan and into East Central Saskatchewan.

The activity will begin this evening with the development of supercell storms along the Montana border that will push northeastward through the late evening. These storms could be quite strong and will be followed by even more development from south of the border after midnight. This second round is expected to be more organized and bringing more widespread impacts as they follow the northeastward trend across Southeastern Saskatchewan through the morning.

These storms could be quite impactful with very large hail that will likely be golf ball-sized, possibly even larger, and widespread damaging wind gusts upwards of 120km/h, as well as one or two tornadoes. There is also the concern of localized flooding with heavy downpours that could bring up to 100mm of rain.

Greatest Severe Thunderstorm Threat for Saturday Afternoon Shifted West; Still Slight Risk for Southern Manitoba

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Following this morning’s thunderstorms, we are still expecting more severe weather for Southern Manitoba later today, however the anticipated strength of those storms has diminished and the area they’re expected to hit has also changed. The strongest storms of the day are now expected in Southern Saskatchewan, but the potential for damaging winds, large hail. and localized flooding still result in a Slight Risk for severe thunderstorms in the Westman, Parkland and Northern Interlake Regions.

The exact timing of these storms is tricky to establish due to uncertainty between weather models, leaving three possible scenarios.

Scenario 1

Large storms could begin to develop in the mid-afternoon just east of the Saskatchewan border in the Parkland Region as isolated supercells which would travel northeastward across the province. Development of additional storms would continue through the evening and early overnight, following the same northeastward trajectory. These storms would then be followed by a more organized cluster of storms crossing through the region Sunday morning.

Scenario 2

Smaller storms could start to develop in the Parkland Region in the mid to late afternoon and quickly become more organized into a strong line that spreads into the Northern Interlake and travels southeastward through the evening before starting to fall apart approaching the Central Plains overnight. In this scenario, the storms Sunday morning would be weak, if they occur at all.

Scenario 3

A handful of small storms could pop-up starting in the later in the afternoon, once again in the Parkland Region, and continuing into the late evening, but not amount to anything too concerning. Then, in the early morning hours, a large cluster of storms could push northeastward into the region from Saskatchewan, followed by a second round of strong storms later in the morning.

Regardless of which of the three scenarios unfolds, it is likely that there will be strong storms in Manitoba over the next 24 hours. The threats from these storms will be the large hail, with up to toonie-size likely and damaging wind gusts that could exceed 100km/h, as well as one or two tornadoes . There is also the concern of localized flooding because these storms are expected to occur over the same area. It’s important to note that the level of uncertainty between weather models means that this could very well end up being a classic “bust” day, but we believe that it is better to be prepared in the event that any one of these scenarios materializes.

Slight and Strong Risk for Severe Thunderstorms Across Southern Manitoba Saturday, Hitting in Multiple Rounds

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It will be a hot day across Southern Manitoba on Saturday, but there will be some active weather, in the form of a line of severe thunderstorms, to contend with before the temperatures start to climb. More storms will hit the region later in the day, but the timing remains a little unclear. Regardless, the risk of large hail and damaging wind gusts, along with the possibility of a tornado makes this a Strong Risk for severe thunderstorms in Southwestern Manitoba, including Brandon, and a Slight Risk across much of the rest of Southern Manitoba.

The first line of storms will make their way into Southwestern Manitoba around sunrise Saturday morning, packing a punch with strong winds and large hail. These storms will lose steam as they travel eastward across the width of the province throughout the morning and into the early afternoon. Following this line of storms, it will be a hot day across the region, feeling closer to 40°C with the humidity, which should provide ample fuel for another wave of storms. The exact timing of this second line of storms is still uncertain. Some models are suggesting that the additional storms could start Saturday evening and make their way across Southern Manitoba overnight and into Sunday morning. On the other hand, there are other models that show the second line of storms developing in the early morning hours of Sunday and continuing into the early afternoon, followed by a third line of storms beginning Sunday evening. Due to this uncertainty, we will likely have a revised forecast for the secondary storm development posted Saturday afternoon.

The threats from these storms will be the large hail, with up to golf ball-size possible, as well as widespread damaging wind gusts that could exceed 100km/h and approach 120km/h, along with the possibility of a tornado or two touching down. There will also be a flooding risk, with these storms expected to bring up to 100mm, particularly to areas that will experience multiple rounds of storms.

UPDATE: Slight Risk for Severe Thunderstorms for Friday Now Extends into Calgary

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In an update to the forecast that was posted yesterday evening, we have extended the boundaries of the Slight Risk region to include Calgary and the entire Highway 2 corridor south of the city. The combination of damaging wind gusts, large hail, and the possibility of an isolated tornado from today’s has resulted in the Slight Risk for this area, along with Lethbridge, Medicine Hat, and Drumheller.

Thunderstorms have already begun to develop in Montana, moving northward towards the border. They will start to cross into Alberta later this afternoon and early evening, spreading across Southern Alberta throughout the rest of the evening and overnight. It’s possible that the storms could become organized into a line that will push northeastward starting later in the evening which will impact a more widespread area than just isolated storms.

The main threat from these storms will be the hail, with up to toonie to timbit-size likely, as well as damaging wind gusts that could exceed 100km/h and even approach 130km/h. At this time, there does not appear to be too much of a flooding risk, with these storms expected to bring less than 50mm of rain over the span of a few hours. An isolated tornado can also not be completely ruled out.

Slight Risk for Severe Storms in Southern Alberta to Finish the Week; Forecast Could be Upgraded

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Friday will be another hot day across Southern Alberta and along with that heat comes severe thunderstorms. A combination of damaging wind gusts, large hail, and the possibility of an isolated tornado means that there will be a Slight Risk in an area that includes Lethbridge, Medicine Hat and north towards Drumheller.

The storms will cross into Alberta from Montana in the south starting in the late afternoon and early evening, spreading across the region throughout the evening and overnight hours. It’s possible that the storms could become organized into a line that will push northeastward starting later in the evening that will impact a more widespread area than just isolated storms.

The main threat from these storms will be the hail, with up to toonie-size likely, as well as damaging wind gusts that could exceed 100km/h. At this time, there does not appear to be too much of a flooding risk, with these storms expected to bring less than 50mm of rain over the span of a few hours. An isolated tornado can also not be completely ruled out. The risk level could change with more data from short-range models so stay tuned for any updates to this forecast.

UPDATE: Isolated Strong Risk for Severe Storms in Southern Saskatchewan Beginning Wednesday Evening

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It will be another stormy day in Southern Saskatchewan on Wednesday, with active weather beginning later in the day and continuing through to Thursday morning. A combination of very large hail, damaging wind gusts and the possibility of tornadoes has led to us upgrading this forecast to a Strong risk, surrounded by a Slight Risk in the Southeastern region of the province.

The storms are anticipated to start in the early evening Wednesday in the southwest as some isolated cells. These individual storms will quickly merge and become large clusters of storms that will move northeastward across Southern Saskatchewan throughout the rest of the evening and into the early morning hours of Thursday. The storms will become more organized as they move across the province, as well as becoming more intense, thus increasing the threat from Marginal, Slight and in an isolated area that includes Regina, a Strong risk.

The main threat from these storms will be the hail, with toonie to timbit size with isolated hail up to golf ball size, as well as damaging wind gusts that could exceed 100km/h. Heavy downpours will be associated with these storms and some areas, particularly in Southeast Saskatchewan, could see over 50mm of rainfall. There is also the risk of these storms producing one or two tornadoes so be sure to keep an eye out for watches and warning being issued by Environment Canada later in the day.