Strong Risk for Severe Thunderstorms Saturday for Parts of Southern Ontario

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We’ve been carefully monitoring the risk of severe thunderstorms developing in Southern, Central and Eastern Ontario today, Saturday, June 29th, 2024. We’ve noticed quite a bit of variability in the model data for a few days now and it’s been a tricky forecast to say the least. However, we’ve believe based on the data that we’ve seen, there is an isolated strong risk for severe thunderstorms today, highlighted in orange in deep southwestern Ontario, stretching over to the Niagara region and western side of the GTHA.

We may even see severe thunderstorms this morning in the deep southwest, followed by more storms this afternoon and evening across much of the region. The main risks are torrential rain with flooding, hail, damaging wind gusts and frequent lightning. We are also seeing a risk for isolated tornadoes with these storms as the environment looks quite robust for the development of supercells.

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In addition to the strong risk, we’ve included a slight risk in yellow that stretches up into the northern side of Southwestern Ontario, through Central Ontario and the rest of the GTHA, and down through areas north of Lake Ontario, ultimately out towards Quebec.

It’s difficult to determine if we’ll see enough clearing of the widespread rain to support strong severe thunderstorms in the slight risk area or if the wash out of precipitation across the region will mitigate how strong these storms can become. Nonetheless, if we do end up seeing more clearing than we’re expecting, this would allow for daytime heating to occur and then we could be dealing with an isolated tornado risk in the slight regions along with a risk for hail, damaging wind gusts, frequent lightning and isolated flooding.

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Last but not least we have a marginal risk in green across the rest of Eastern Ontario and even up into the southern side of Northeastern Ontario, towards Manitoulin Island, Sudbury, etc. Up there, models have not suggested the storms will be that strong but in these widespread severe weather environments, if the right storm hits the right lake breeze or outflow boundary we could end up seeing severe thunderstorm activity. This is why we’ve got a blanket green risk across the rest of the region.

Long story slight longer, keep your eyes to the skies folks! We’ll be watching closely and live-streaming at some point today to closely monitor these storms as they could quickly become severe so we’ll need to move fast with our custom severe weather notifications. To receive those instantly along with any Environment Canada alerts, download our free app Instant Weather or if you want to ensure the fastest and most robust delivery of alerts, you can subscribe to our class leading Text Message Alerts.

More details ASAP and to get notified when we go live, subscribe to our YouTube channel for free.

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Slight Risk for Severe Thunderstorms on Wednesday for Southwestern and Central Ontario

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There is a slight risk of severe thunderstorms this afternoon and evening (Wednesday, June 26, 2024) in parts of southwestern Ontario and Central Ontario, highlighted in yellow on our forecast map. There is, however, some uncertainty regarding the location and timing of these storms. Having said that, if a strong storm does decide to develop off of Lake Huron near Kincardine early this afternoon (12p - 3p), we could have a supercell (rotating storm) on our hands that should track east towards the Barrie region by (4-7pm).

Some models are suggesting that strong storm development is possible in that area and others are suggesting no storms will develop in that region. If this anticipated storm does occur, there could be an isolated tornado risk with it along with a risk for hail, damaging wind gusts, frequent lightning and torrential rain.

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Deeper in southwestern Ontario, we're more confident about the development of thunderstorms. For areas north of Lake Erie, from Windsor and Essex County, up through the Sarnia region, reaching over towards the London corridor and perhaps towards the Niagara region, we're anticipating a cluster of storms developing this afternoon and pushing east through the evening hours. These storms could bring with them damaging wind gusts, hail, frequent lightning, torrential rain and some flooding risk. Isolated tornado development cannot be ruled out in that region either.

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We're also seeing some marginal risks for thunderstorm development in parts of Eastern Ontario, developing either in the late afternoon or evening hours. The best chance in Eastern Ontario would be in areas north of Lake Ontario, tracking to the southeast, possibly towards the Kingston and Cornwall regions. Overall, the risk in eastern Ontario is marginal. However, hail, damaging wind gusts, lightning, torrential rain cannot be ruled out. The tornado risk would be quite low, but stranger things have happened in our region so we'll be watching closely to see if any storms develop rotation.

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We're going to be watching closely to see exactly where any storms develop this afternoon and evening and we may go live to cover the storms if they look strong enough so definitely look out for that on our YouTube page and if it gets particularly intense, we'll also go live on our Facebook pages.

Have a plan today folks and certainly keep an eye on our free mobile app; Instant Weather for any notifications regarding rotating storms, damaging wind gusts, etc.

More details ASAP.

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Potential Severe Storm Risk on Saturday for Greater Toronto Area & Southwestern Ontario

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After the first prolonged heatwave of the season in Ontario this past week, some relief is in sight just in time for the weekend. While the heat warnings for much of Southern Ontario have ended, they continue for one more day in Southwestern Ontario.

Unfortunately, the milder air will be accompanied by active weather throughout the weekend, including the risk of severe thunderstorms in the south and significant rainfall for the northern parts of the region.

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thunderstorm risk checklist

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There is a slight risk for severe storms beginning early Saturday afternoon and continuing into the evening hours. This includes areas east of Lake Huron, extending into parts of the Greater Toronto Area.

The main threats will be damaging wind gusts approaching 90-100 km/h and marginally severe hail. Based on the expected environment, we may also see an isolated tornado, although the overall tornado risk is on the lower side.

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Storms are expected to pop up somewhere along the corridor stretching from Lake Simcoe southwest into Orangeville and Kitchener-Waterloo starting around 1 to 3 PM. Additional storm development may occur over Lake Huron and track onshore between Wiarton and Grand Bend throughout the afternoon.

Current indications suggest that any storms developing today will move slowly, which means flooding could be a big concern, especially if they reach the more urban areas around the Golden Horseshoe and begin to ‘train’ over a specific location.

Any of these storms will have the potential to bring severe weather, including wind gusts and hail. The tornado threat is highest earlier in the day to the northwest of the GTA, including Grey, Bruce, Wellington, Dufferin and Simcoe counties.

The storm threat will diminish by early evening as the sun sets and the daylight heating fueling the storm activity shuts off. However, non-severe thunderstorms will remain possible overnight into Sunday morning, especially for Eastern Ontario.

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Further north, heavy rain will move across Central and Northeastern Ontario, with embedded pockets of non-severe thunderstorm activity starting this afternoon. Eastern Ontario will begin to experience rain by late evening. This is expected to continue through the overnight hours and into Sunday, with substantial rainfall totals approaching 100mm by the end of the weekend.

Environment Canada has issued a rainfall warning for the affected region. We will have a more detailed update on the significant rainfall in a separate forecast later today.

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More Isolated Severe Risks on Thursday for Southern Ontario

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For this afternoon and evening (Thurs, June 20th, 2024), most of southern Ontario should pay attention to the skies as there's another isolated risk for severe thunderstorms, highlighted in yellow on our map. The primary threats with these storms include damaging wind gusts, hail, isolated flooding, and frequent lightning. Although the potential for an isolated tornado exists, the overall risk remains low. Remember to keep an eye on our free app Instant Weather for any notifications.

The areas with a slight risk include deep southwestern Ontario, covering locations such as Windsor, Essex County, and beyond. Additionally, parts of the Greater Toronto and Hamilton Area (GTHA), the Niagara region, and potentially Kitchener and Woodstock areas are also in the yellow zone. These regions may experience storms depending on where they develop, but keep in mind that most of the community will not see these storms as they'll be quite isolated. Furthermore, eastern Ontario faces a slight risk this afternoon, and this area may witness the strongest thunderstorms of the day. This region has the best chance to see severe hail and perhaps an isolated tornado, although the overall tornado risk is still fairly low.

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In addition to the slight risk zones, a broader area marked in green indicates a marginal risk for much of the region, where pop-up storms could occur this afternoon and evening. These storms will be very isolated, so most locations will likely remain storm-free. However, if a storm does develop in your area, the main risks are flooding, hail, and frequent lightning. Isolated damaging winds and perhaps a brief spin-up cannot be entirely ruled out in the green zones, but the overall risk is quite low.

Given the variability and unpredictability of these pop-up storms, it's essential to pay attention to notifications this afternoon and evening. Ensure your notifications are turned on and have a plan in place in case severe weather occurs in your area. Stay safe, folks! As always, we'll be watching.

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Isolated Slight Severe Threat on Wednesday for Deep Southwestern Ontario

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For this afternoon and evening (Wed, June 19th, 2024), deep southwestern Ontario should be keeping an eye to the skies as there's a slight risk of severe thunderstorms in the area highlighted in yellow on our map. The primary threats posed by these storms include damaging wind gusts, hail, isolated flooding, and frequent lightning. While the potential for an isolated tornado exists, the overall risk remains quite low. Nonetheless, best to keep an eye on our free app Instant Weather for any notifications.

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In addition to the slight risk zone, a broader area marked in green indicates a marginal risk of isolated severe thunderstorms. These pop-up storms could occur at any time this afternoon and evening. Due to their isolated nature, most locations will not experience any storms at all. However, those who do encounter a storm could face risks such as flooding, hail, and frequent lightning. Within the marginal region, the chances of experiencing isolated damaging winds or a brief tornado are quite low. However, they cannot be completely ruled out.

Given the variability and unpredictability of these pop-up storms, it's important to pay attention today! Make sure your notifications are turned on and have a plan in place in case severe weather occurs in your area. Stay safe folks! We’ll be watching closely.

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Parts of Southern Ontario to Feel Near 40°C on Monday as Prolonged Heat Wave Begins

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The feeling of summer will certainly be in the air across Southern Ontario throughout the upcoming week. A blast of warm, tropical air from the Gulf of Mexico will bring a multi-day heatwave with temperatures soaring well above 30°C starting Monday. Once you factor in the humidex, it could feel closer to 40°C, especially towards the middle of the week.

This all kicks off on Monday, with the heat building into the southwestern part of the region. Temperatures in Deep Southwestern Ontario, including Windsor, Leamington, Chatham, Sarnia, and London, could reach the low to mid-30s by the afternoon. With the rising humidity, it could feel closer to the upper 30s or even low 40s.

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The rest of Southern Ontario will see daytime highs in the upper 20s or low 30s away from the Great Lakes shores. Again, the humidity will add to the sweltering heat, making it feel like the mid to upper 30s. This includes much of Central and Eastern Ontario along with the Golden Horseshoe region away from the lake.

Those around the shorelines of Lake Ontario, Erie, Huron, and Georgian Bay can expect slightly cooler temperatures thanks to the lakes providing a bit of a cooling effect. Locations such as Toronto, Burlington, Tobermory, Parry Sound, and Manitoulin Island could offer some relief from the heat.

Temperatures here will likely struggle to exceed 30°C, and the humidity will make it feel at most like the low 30s. It’s not a huge relief, but still notable given the near 40°C humidex expected further inland.

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Even as we head into the overnight, we won’t see much of a cooldown to provide a break from the oppressive heat. Overnight temperatures are expected to bottom out in the upper teens or low 20s. However, the good news is that the humidity will mainly be a problem during the day, so expect some less stuffy temperatures after the sun goes down.

The same story is expected to play out on Tuesday and Wednesday. However, the heat is only expected to become more intense as the week progresses. Widespread temperatures, even without the humidex, could exceed 30°C almost everywhere in Southern Ontario. The humidex will make it feel like the 40s and, unlike on Monday, won’t be just contained to the Deep Southwest.

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Concerningly, the overnight lows on Tuesday and Wednesday could only get down to the mid-20s and climb back into the 30s by 10-11 AM. Those air conditioners and fans will certainly be running full blast all night long to keep up with this warmth.

It won’t be until later in the week that we finally get some fresher air just in time for the weekend. However, we are closely watching the end of the week for a potential severe thunderstorm threat. Isolated storms are possible earlier in the week, which we will be closely watching, but it appears that more widespread storm development won’t be a concern until Thursday and Friday.

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During extreme heat, it is crucial to stay safe and take preventive measures to avoid heat-related illnesses. Make sure to stay hydrated by drinking plenty of water, even if you don't feel thirsty. Avoid beverages that can dehydrate you, such as alcohol and caffeinated drinks.

Try to stay indoors during the hottest parts of the day, usually between 10 AM and 4 PM. If you must be outside, wear lightweight, light-coloured, and loose-fitting clothing and apply sunscreen to protect your skin from harmful UV rays.

Additionally, never leave children or pets in a parked car, as temperatures can quickly become dangerously high. Check on elderly neighbours and family members, as they are more vulnerable to heat-related illnesses.

Utilize air conditioning if possible, or visit public places like shopping malls, libraries, or community centers to stay cool. Be aware of the signs of heat exhaustion and heat stroke, such as dizziness, nausea, headache, and confusion.

Call 911 immediately if you believe you or someone around you is experiencing heat stroke.

Widespread Strong Severe Threat on Thursday for Southern & Northeastern Ontario

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The arrival of Ontario’s first prolonged heatwave of the season will start with a bang as a potent severe threat is expected on Thursday. Temperatures are predicted to soar into the upper 20s or even low 30s, providing a preview of what next week will feel like.

This heat, combined with an approaching cold front, is expected to spark off some intense storms during the afternoon and evening hours across Southern and Northeastern Ontario. There is a widespread 'strong' risk for severe weather, covering much of Central, Southwestern, and Northeastern Ontario, where damaging wind gusts, large hail, and a few tornadoes are possible.

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In our preliminary forecast, we included a 'significant' risk zone on our map. While this event still looks quite dangerous, we have decided to downgrade to a 'strong' risk for our highest level in this forecast. To be clear, severe storms still seem almost certain in a large swath of Southern Ontario into Northeastern Ontario during the afternoon and early evening hours.

This isn’t to downplay what could still be a dangerous event, but we are careful about only using the higher severe levels for the strongest severe risks. The data no longer supports the criteria for our significant risk category. We feel confident that the 'strong' risk will be sufficient to cover these storms today.

We are already seeing storm development across Northeastern Ontario with severe thunderstorm warnings issued by Environment Canada as of 12 PM. Based on the latest models, further storm development is expected in a line stretching from Elliot Lake, across Manitoulin Island, and over Lake Huron between 2-4 PM.

This line will slowly track east, coming onshore between the Bruce Peninsula and Goderich around 4-6 PM. There is some uncertainty in the exact timing, so this may be off by a few hours if it arrives earlier or later than expected.

Additionally, we may see some isolated storm development ahead of this line across Central Ontario, especially around Georgian Bay and Lake Simcoe, anytime between 4 to 8 PM. These isolated storms will have a strong environment to work with and could present severe hazards including hail up to the size of golf balls, damaging wind gusts, and tornadoes.

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By the evening, the focus will shift towards more of a damaging wind threat, although an isolated tornado could still be possible. An organized line of strong to severe storms is expected to stretch from Algonquin Park through Lake Simcoe and to the southwest into London and Kitchener. This line will track east towards the Golden Horseshoe, Peterborough, and eventually the Ottawa Valley.

Again, the timing is still uncertain as some models indicate the line reaching the Greater Toronto Area and Ottawa Valley by early evening while others suggest it won’t arrive until closer to midnight. The later the storm arrives, the weaker it will likely be as the prime environment fueling these storms will quickly fade away after sunset.

Heavy rain and non-severe thunderstorms will continue throughout Eastern Ontario during the overnight hours and into Friday morning. However, the severe threat for all of Southern Ontario will come to an end by midnight.

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thunderstorm risk checklist

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To help you better understand how we come up with our forecast, here’s a look at the checklist we used to determine the threat for today.

We expect that some of the storms could produce widespread wind damage along with hail up to the size of golf balls. This correlates to a 'strong' (level 3) risk according to our criteria.

Our previous forecast, where we had a 'significant' (level 4) risk, was due to the potential for destructive wind gusts. However, based on the latest data, we no longer have enough confidence that the wind gust threat will reach the threshold to be considered widespread and destructive.

The tornado threat remains the same as our preliminary forecast, which would be considered a 'slight' (level 2) risk. We don’t expect several tornadoes today as this is primarily a wind and hail-driven severe event, but one or two tornadoes somewhere in our strong and slight risk zones are possible.

The flooding threat with these storms is marginal as the line will be moving quite fast as it sweeps across the province. Most areas will see between 20 to 40 mm of rain with locally up to 50-75 mm.

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For Northeastern Ontario, there is a similar risk for strong severe storms in locations including Timmins, Kirkland Lake, and Temiskaming Shores. The tornado threat may actually be slightly higher in this area as we expect more isolated storm activity compared to the south.

Storms have already started to develop in parts of Northeastern Ontario and are expected to continue throughout the afternoon as they slowly track towards the Quebec border. Additional storms may develop during the evening hours, but the storm threat should diminish by 9 to 10 PM.

Potentially Significant Severe Threat in Southern Ontario on Thursday; Tornadoes, Destructive Wind Gusts and Large Hail Possible

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THIS FORECAST HAS BEEN UPDATED

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Confidence is growing for what could be Southern Ontario’s strongest severe thunderstorm risk of the year so far. The latest model data points to a potent environment developing throughout the afternoon and evening on Thursday.

As a result, we have issued a significant (level 4/5) severe risk due to the widespread severe threat. Locations affected include Orangeville, Collingwood, Newmarket, Barrie, Orillia, Midland, Peterborough, Bracebridge, Huntsville, Parry Sound, Algonquin Park, and North Bay.

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These threats could include destructive wind gusts over 100-110 km/h (potentially up to 125 km/h) and large hail up to the size of toonies or golf balls. Tornadoes are also likely, especially along the Barrie, Orillia to Muskoka corridor, where models show a strong agreement on this area featuring the most intense environment.

The surrounding region, including the Lake Huron shoreline extending through Kitchener and into the Greater Toronto Area, has a strong risk of severe thunderstorms. The environment remains quite favourable for severe weather here, though there is more uncertainty about storm development. If storms form, they will be able to take advantage of the strong environment.

Those in Eastern Ontario along the St. Lawrence and Deep Southwestern Ontario have a marginal severe risk. This is because the environment is weaker and likely won’t support any major severe weather threats.

More detailed timing information will be coming in an updated forecast on Wednesday or early Thursday.

NOTE: This is a preliminary forecast and is subject to change. Please check back for the latest updates so you can properly prepare as we get closer to the event.

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Northern Ontario could also see some stormy weather on Thursday. We currently have a slight risk for a portion of Northeastern Ontario along the Quebec border and stretching southward towards Georgian Bay. North Bay likely has the strongest risk of anywhere else in Northern Ontario.

The risk will lessen further to the north and west. However, Northwestern Ontario could be dealing with quite an active day on Wednesday. The main threat will be large hail and possibly some tornadoes. More details on that will follow soon, including a full forecast.

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Thunderstorms Could Bring Damaging Wind Gusts & Flooding Risk to Eastern Ontario on Thursday

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After a line of severe storms tracked into Deep Southwestern Ontario yesterday, leading to reports of damage throughout the Sarnia region, the focus is shifting to the east on Thursday.

There is a slight risk for severe storms mainly during the early to mid-afternoon hours across parts of Eastern Ontario. A cluster of storms is expected to develop between Pembroke and Picton around lunchtime. These slow-moving storms will gradually track northeast towards Smiths Falls, Kingston, Brockville, Ottawa, and Cornwall between 1 and 5 PM.

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Based on the latest data, the storms could potentially produce a significant amount of rain within a short timeframe. Some models are projecting upwards of 100 to 150mm of rain in parts of the Ottawa Valley by the end of the afternoon. This could cause flash flooding, especially if the heavier rain locks in over the more urban areas of Ottawa.

Besides the rain, we can’t rule out localized pockets of damaging wind gusts. Small hail up to the size of nickels is also possible. While the tornado risk is fairly low, the possibility of a brief spin-up exists, as similar events have led to isolated tornadoes.

The storm threat for Eastern Ontario will end by early evening as the line of storms slowly moves into Quebec and out of our region.

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Moving to the west, there are indications of pop-up storms developing during the late afternoon to early evening around Lake Ontario. The environment is particularly focused around the Brantford, Hamilton, and Niagara regions.

In most cases, these storms should remain non-severe, and most areas won’t even see a storm due to how extremely localized they will be—if they even develop. However, there is a questionable risk for marginally severe winds, so we have decided to place this area in a marginal (level 1) severe risk. Flooding could also be a concern if a storm lingers in a particular area for an extended period, especially if it gets into a more urban area like Hamilton.

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The pop-up storm threat will diminish towards sunset, although we could see some nocturnal non-severe storms after midnight around the Georgian Bay and Lake Simcoe area.

Widespread Severe Thunderstorm Risk Across Southern & Northeastern Ontario on Wednesday

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As we welcome the first days of June across Southern Ontario, the warmer temperatures are a noticeable change from the end of May. Just last week, we were dealing with frost advisories in parts of the province. Now, temperatures are well into the 20s or even low 30s.

However, the bubbling heat will come at a cost with the return of thunderstorms, fueled by the hot temperatures. A line of storms, along with isolated cells ahead of it, is expected to extend from Northeastern Ontario southward into Southwestern Ontario sometime Wednesday afternoon or early evening.

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Based on the predicted environment, these storms will have the potential to bring a ‘slight’ severe risk with damaging wind gusts up to 100 km/h as the primary threat. Hail up to the size of quarters and an isolated tornado threat can’t be ruled out.

There is some disagreement on exactly where this line will develop, which is associated with a cold front cutting across the region and bringing an end to the warmer temperatures. When this front arrives will be key to the overall storm threat. While storms could develop ahead of the line, the bulk of the severe threat will be concentrated with the squall line setup stretching from Lake Superior down into Michigan.

The latest data suggests that this line could form earlier in the day and start to cross over Lake Huron by the late afternoon or around the dinner hour. If it does end up arriving this early, the storms will be moving into a strong environment, allowing the squall line to potentially bring widespread damaging wind gusts as it tracks into Southwestern Ontario.

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On the other hand, a later arrival in the evening would likely lead to the line of storms being weaker than expected and may only reach marginally severe levels. We do expect some gradual weakening in the line throughout the evening as it tracks into Central and Eastern Ontario by the mid to late evening hours. Non-severe thunderstorms could continue overnight and into early Thursday morning for Eastern Ontario.

As mentioned, we could see a few isolated cells pop up in Southwestern Ontario and maybe even around Lake Simcoe and Georgian Bay during the late afternoon ahead of the main line. If these storms can establish themselves, they could bring all severe hazards, including damaging wind gusts and up to toonie-sized hail. A tornado can’t be ruled out as these storms will have all the environment to themselves.

It should be noted that confidence in the isolated storms ahead of the line is questionable in Southern Ontario but could be more of a problem as we look at Northern Ontario.

For Northeastern Ontario, the confidence in isolated storms is much higher as we could see several cells develop along the Sudbury to Geraldton corridor during the afternoon and early evening. Similarly to Southern Ontario, these storms could bring damaging wind gusts and large hail, and the tornado risk is a little more elevated here due to a stronger environment.

This is also in addition to the squall line that will cross into the region from Lake Superior sometime around the dinner hour. At this point, the main threat will be damaging wind gusts up to 100 km/h, but we could still see some marginally severe hail and an isolated tornado. The squall line will gradually weaken as it tracks towards Quebec by the midnight hour.

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There is a slight risk for severe storms stretching from Manitoulin Island through Elliot Lake and into Geraldton and Armstrong. This also includes the Lake Superior shoreline between Sault Ste. Marie and Marathon. The rest of Northeastern Ontario has a marginal severe risk.

For Northwestern Ontario, there could be a few pop-up storms during the afternoon and evening with a marginal risk around Thunder Bay. This risk will quickly diminish after sunset, which is providing the fuel to the pop-up cells.

Strong Severe Risk With Tornadoes Possible on Monday in Eastern Ontario Including Ottawa & Kingston

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The severe weather season is certainly off to a busy start across Southern Ontario as we enter the final week of May. Just last week, we had our first 'strong' severe weather risk of the season, and this week, we're facing our second strong severe weather threat for Monday afternoon.

While last week's risk predominantly affected Central and Southwestern Ontario, the strongest risk for Monday will shift to Eastern Ontario, including the Ottawa Valley. Multiple rounds of storms starting late Monday morning and continuing throughout the afternoon could bring damaging wind gusts and large hail. A few tornadoes are also possible, with the environment potentially being the strongest we've seen this season.

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Further to the south and west, there's an expansive risk for marginally severe storms during the morning and early afternoon hours. This is mainly due to the flooding threat, as models indicate multiple rounds of storms could impact the Golden Horseshoe region into Central Ontario. Some areas may approach 75 to 100mm of rain, with the bulk of that coming in just a few hours. Nickel-sized hail and 90km/h wind gusts are also possible.

As of Sunday night, a decaying line of non-severe thunderstorms is tracking across Southern Ontario and is expected to continue into Central and Eastern Ontario during the predawn hours. Just after sunrise on Monday, another cluster of storms is expected to cross over Lake Erie and track toward the Golden Horseshoe.

These storms should be predominantly non-severe, especially given the early morning timing. However, some models indicate an environment building toward the late morning hours that may support storm intensification to marginally severe levels.

This includes the Greater Toronto Area and Central Ontario around Lake Simcoe. Again, flooding would be the main concern, especially with the heaviest rain potentially targeting the urban core of the GTA. The tornado risk should be fairly low at this point in the day, with the main focus being hail and strong wind gusts.

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This same complex of storms will track into Eastern Ontario by the early afternoon. The arrival of this line will be critical. If it arrives too early, it could wipe out the environment needed for severe storms for the day. But if it arrives much earlier, like during the morning hours and clears out before noon, the environment will have lots of time to recover with more isolated storms later in the day.

Currently, the consensus is this line arriving around 1-3 PM with additional storms forming ahead of the main line. The actual line may also further intensify as it approaches Eastern Ontario, with potentially destructive winds developing from Kingston to Ottawa and tracking to the northeast.

If we get isolated storm development ahead of the line, they could pose all types of severe hazards, including large hail up to the size of toonies or even ping-pong balls, damaging wind gusts, and potentially tornadoes.

The tornado threat is highest with the isolated storms, but we could also see some embedded rotation within the main line. The main line will feature mostly destructive wind gust threats, with gusts potentially reaching 100-120 km/h, although localized large hail can't be ruled out.

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We currently expect the most severe weather to occur between 1 to 5 PM for Eastern Ontario, ending later the further east you are. Depending on timing, we may see additional storm development behind the early afternoon line of storms if the environment recovers quickly enough before the sun goes down.

This includes Southwestern Ontario and Central Ontario, which could see pop-up storms during the late afternoon or early evening. It's questionable if they will have enough fuel to reach severe levels and may just fizzle out. However, a few of these storms could become marginally severe. This is very preliminary and subject to change once we see how the morning and early afternoon storms affect the environment.

The storm threat will end by the early evening hours across Southern Ontario, but more rain is expected to continue overnight into Tuesday morning. We could see some embedded non-severe thunderstorms overnight as well.

Widespread Strong Severe Thunderstorm & Tornado Risk for Southern Ontario on Wednesday

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The multi-day severe weather threat continues in Southern Ontario for Wednesday, with what could be the strongest risk of the year so far. Several rounds of storms are expected this afternoon and early evening throughout Central and Eastern Ontario, along with the Golden Horseshoe.

The biggest concern is currently focused on an area stretching from Lake Simcoe northeast into Muskoka and Algonquin Park. All the latest data points to a very potent environment developing early this afternoon, which would be favourable for storms to quickly become severe with large hail, destructive wind gusts, and tornadoes.

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As a result, our forecast includes the first ‘strong’ (level 3) severe risk of the season in Ontario. This is primarily due to the wind threat, which could be quite widespread and intense as we see multiple lines of storms. One or two tornadoes are also possible within the ‘strong’ and ‘slight’ severe risk zones, which encompass almost all of Southern Ontario except for Southwestern Ontario.

The ‘strong’ severe risk includes Kitchener, Orangeville, Barrie, Orillia, Collingwood, Midland, Bracebridge, Parry Sound, Huntsville, Sundridge, Bancroft, Algonquin Park, Deep River And Pembroke.

The tornado threat is highest across Central Ontario, where isolated severe supercells could develop. However, tornadoes could occur anywhere within the severe risk zones, so remain vigilant regardless of your location.

Timing is tricky to nail down as we are looking at multiple rounds of storms, and models are not in full agreement on when and where these storms will occur. Here is a rough estimate of each round of storms, though this may shift throughout the day.

Current indications show isolated storms developing between Lake Huron and Georgian Bay along the Goderich to Parry Sound corridor. This could happen as early as 12-1 PM as the environment builds ahead of these storms.

They are expected to track into Simcoe County and regions east of Georgian Bay by early afternoon. At this point, they will likely become severe, tracking into the Muskoka, Parry Sound, and Sundridge regions.

All severe threats are possible as they track northeast towards Algonquin Park, Bancroft, and eventually the Quebec border. Large hail and tornadoes are possible within these clusters of storms, especially early in their lifespan before they begin to bow out and become more of a wind gust threat.

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For those who see this first line of storms, don’t be caught off guard! More storm development is expected across Georgian Bay and to the south around Lake Simcoe throughout the afternoon hours.

Another cluster of storms in the late afternoon may follow a similar track as the earlier storms through Simcoe County, Kawartha Lakes, Muskoka, and Bancroft. This line of storms will continue across Central Ontario and potentially into the Ottawa Valley by dinner time.

Some isolated storms may also form over Lake Erie and potentially track into the Niagara region during the afternoon. Additionally, we are seeing some indications of a few isolated storms forming just before sunset around 6 to 8 PM between Orangeville and Kitchener, tracking into parts of the Greater Toronto Area.

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This is a concern because the environment at this time may be stronger than anything we’ve seen earlier in the day. While storm development is more questionable, if it does happen, these storms could certainly pose a tornado threat.

The severe threat will continue into Eastern Ontario during the evening hours as the second round of storms moves into the area. At this point, it will likely be mainly a wind risk, however, an isolated tornado can’t be ruled out—even after sunset. The storm risk should diminish by midnight as the line of storms moves into Quebec.

Severe Storm Threat Shifts to Eastern Ontario on Tuesday With Tornado Risk for the Ottawa Valley

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Southern Ontario is currently enjoying an unusually warm stretch of late May weather, expected to continue for a few more days. With this heat, the risk of thunderstorm activity also remains present, particularly on Tuesday.

While storm activity was primarily concentrated in Southwestern Ontario and parts of the Golden Horseshoe on Victoria Day, the focus will shift eastward for Tuesday afternoon and evening. Isolated storms have already started to develop east of Georgian Bay and are expected to strengthen as they move into Central and Eastern Ontario during the afternoon.

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A broad area, from the Ottawa Valley southwest toward Lake Simcoe, is under a slight risk of severe weather today. Although not everyone will experience a storm, those that do could face severe weather threats, including hail up to the size of toonies, wind gusts of 100 km/h, and possibly an isolated tornado. Areas potentially impacted include Peterborough, Bancroft, Pembroke, Renfrew, Smiths Falls, Ottawa, and Cornwall.

The primary risk period is slated for the late afternoon to early evening. The Ottawa region could see storm activity around the dinner hour. Most storm activity is expected to wane between 8 and 9 PM as the sun sets and the heating that fuels these storms diminishes.

In addition to Eastern Ontario, there's a questionable storm threat in Deep Southwestern Ontario along the Michigan border. There are indications that an isolated storm or two could cross the border, potentially bringing marginally severe threats such as quarter-sized hail and 90 km/h wind gusts. While the risk of a tornado is low, it cannot be completely discounted.

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Looking ahead to Wednesday, the storm threat across Southern Ontario appears quite potent. Models currently disagree on storm development; some predict limited activity while others forecast an intense line of storms during the afternoon and evening. The environment is expected to be conducive to severe weather if storms do develop. We will provide more details in an upcoming forecast.

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Isolated Severe Thunderstorms Could Impact Victoria Day Celebrations in Southern Ontario

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Southern Ontario has enjoyed stellar weather conditions throughout the long weekend, with temperatures reaching 30°C in some locations on Sunday! However, it looks like this hot weather will cause the long weekend to end with a bang—and not the kind of bang you see with fireworks.

The hot, humid air across Southern Ontario will provide the perfect fuel for isolated pop-up storms to develop later on Monday afternoon and continue into the evening. Although these storms will be small and very isolated, they could still pack a punch with up to quarter-sized hail, 90 km/h wind gusts, and potential flooding due to their slow-moving nature.

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The primary risk for this storm activity is around the Lake Simcoe shoreline and southwest near Lake Huron. It’s important to note that not everyone will experience a storm today, and there’s a good chance that most areas will remain dry. If you do encounter a storm, it could certainly have the potential to bring severe weather.

At this point, the tornado threat is relatively low, but a brief spin-up or even a landspout (non-supercell) tornado can't be ruled out with these pulse storms. The pop-up storm threat will diminish after sunset as the daylight heating fueling these storms disappears.

In addition to the severe threat during the day, we are closely monitoring the expected arrival of a decaying line of storms from Michigan overnight. This should be mostly non-severe as it crosses over Lake Huron and Georgian Bay early Tuesday morning. However, we may see some marginally severe wind gusts and perhaps some small hail as it tracks through Central Ontario and into Eastern Ontario by late morning.

Tuesday morning's convection will be crucial for setting the stage for a potentially severe threat later on in the afternoon. Current indications suggest a fairly potent environment across parts of Eastern Ontario, especially the Ottawa Valley and along the Quebec border.

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If storms develop, we could see the risk of large hail, damaging wind gusts, and maybe even one or two tornadoes. It’s currently looking like a slight (level 2) risk, but we may have to introduce a localized strong (level 3) risk zone if models increase in intensity. A full forecast will be issued later today or early tomorrow.

Wednesday continues to appear as the most intense day for potential severe weather this week, with almost all of Southern Ontario potentially in the bullseye. However, it’s unclear if storms will actually be able to develop and take advantage of the prime environment over Southern Ontario. We will continue to monitor the situation and provide more details soon.

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Elevated Severe Thunderstorm Risk in Parts of Southern Ontario on Monday

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After a damp and somewhat chilly weekend across Southern Ontario, the heat has returned to kick off the week. Many areas in Southwestern Ontario, extending into the Golden Horseshoe and Central Ontario, are expecting daytime highs in the mid-20s on Monday. There's even a slight chance that those in Deep Southwestern Ontario, including Windsor and Chatham, could hit 30°C for the first time this year!

However, this heat will also provide the fuel for some thunderstorm activity during the afternoon and evening hours. Some of these storms have the potential to become severe, with the main threat being large hail up to the size of toonies or ping-pong balls. Marginally severe wind gusts around 90 km/h are also possible, and an isolated tornado cannot be ruled out.

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The threat for severe weather stretches from the Lake Huron shoreline, eastward through the Greater Toronto Area and around the Lake Simcoe area. There could also be some severe storms in Eastern Ontario, especially around the Peterborough, Bancroft, and Tweed regions.

We expect storms will begin to fire sometime between 3 to 6 PM along a line extending from Lake Huron to Bancroft. Keep in mind that these cells will be extremely localized, and most areas may not even see a storm today. However, based on the expected environment, any storms that develop will have the potential to quickly become severe and will likely start producing severe hail, which is the main concern with these pulse-like storms.

Current indications suggest two main clusters of storms will develop, with the first cluster located over Lake Huron and tracking through Huron, Grey, Bruce, Dufferin, and Wellington counties. The other cluster will be located around Kawartha Lake, Halliburton, Peterborough, and Bancroft. These storms will likely weaken as they track further into Eastern Ontario where the environment is less favorable to support severe weather.

By the early evening hours, the cluster of storms east of Lake Huron will continue to mature with all severe threats on the table including very large hail, strong wind gusts, and maybe even an isolated tornado. They are expected to track into Simcoe County and York Region around Lake Simcoe by 6 to 8 PM.

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By the mid to late evening, daylight will begin to fade, reducing the daylight heating that is fueling these storms. They are expected to track into Central Ontario, including Kawartha Lakes and Halliburton, as they gradually weaken once nightfall occurs. We could still see some small hail and strong wind gusts with these storms throughout Eastern Ontario until around midnight.

Non-severe thunderstorms are expected to continue along that same corridor throughout the overnight hours. While we don’t expect any severe threats overnight, flooding could become an issue as multiple rounds of storms train over a particular region.

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Severe Storms Could Bring Golf Ball-Sized Hail & Isolated Tornado Risk to Parts of Southwestern Ontario Late Tuesday

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Are Tornado Tuesdays making a comeback this year in Southern Ontario? It seems that the first full week of May will begin on a stormy note, with a looming severe thunderstorm risk starting Tuesday evening in Deep Southwestern Ontario.

However, the severe threat will be very localized, focusing on Windsor, Amherstburg, Pelee Island, and Leamington. Based on the latest data, the environment in these areas could support the development of storms capable of producing large hail.

Severe wind gusts are also possible, but the main concern is hail, as these storms are expected to be fairly elevated. The hail could be quite large, potentially reaching the size of ping-pong balls or even golf balls.

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Regarding the tornado threat, the elevated nature of these storms should limit the potential for any rotation to reach the surface and produce a tornado.

However, there is a fairly strong environment stateside that could support tornadic activity, and we can’t completely rule out a rogue storm. This is especially true around Leamington and Pelee Island, where the environment is strongest.

Isolated storms are expected to begin popping up over Indiana, Michigan, and Ohio sometime during the late afternoon and early evening. This is where the severe risk will be the strongest, likely leading to several tornadoes and very large hail.

As these storms mature later in the evening, they will track towards Deep Southwestern Ontario around 8 to 11 PM. There is some uncertainty about how well these storms will maintain their strength due to the lack of daylight heating and the cold waters of Lake Erie, which prevent the environment from extending too far north into our region. If the storms arrive earlier than expected, the severe threat could increase, as daylight heating will still be in effect and help fuel the storms.

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Widespread non-severe thunderstorm activity is expected to spread across Southwestern Ontario and into parts of the Golden Horseshoe around midnight. At this point, the storms are not expected to pose any severe threats, but small hail and strong wind gusts cannot be completely ruled out.

Those around Georgian Bay and into Northeastern Ontario, including Sudbury and North Bay, could be awakened by some noisy storms early Wednesday morning. These storms are also expected to remain non-severe.

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Severe Thunderstorm Risk to Kick Off the Week in Southwestern Ontario on Monday

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It has been quite an active few days when it comes to severe weather across the U.S., with a multi-day tornado outbreak leading to devastating scenes in Nebraska, Iowa, and Oklahoma.

Now, the severe weather threat shifts northeast, including the potential for strong storms in Southwestern Ontario starting Monday afternoon and continuing into the evening hours.

Thankfully, the threat here doesn’t appear to be as severe as what was experienced over the weekend in the U.S. However, we could still see damaging wind gusts of 90 to 100 km/h, hail up to the size of quarters, and there's a low chance of an isolated tornado.

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Storms have already started popping up over Michigan as of the early afternoon, and the latest data suggests that the environment is favourable for continued strengthening as they track northeast.

These storms are expected to cross over Lake Huron sometime between 2 to 5 PM and make landfall between Grand Bend and Kincardine. Strong wind gusts and an isolated tornado risk are the main threats with this cluster of storms.

Further south, there may be a second cluster of storms moving into the Windsor area sometime in the early to mid-evening hours. Some models suggest this won’t occur until after sunset, which would lead to a lower severe threat as the effects of daylight heating diminish.

If the storms arrive earlier than expected, the environment would be capable of supporting storms with damaging wind gusts and small hail as the main threats. Again, the tornado risk is low, but we can’t completely rule out a brief spin-up.

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Non-severe thunderstorms will continue throughout the overnight hours into Tuesday morning. This risk extends from Southwestern Ontario through the Golden Horseshoe and into Eastern Ontario along the Lake Ontario shoreline.

Severe Thunderstorms Target Parts of Southwestern Ontario on Wednesday With Tornado Threat

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The saying "April showers bring May flowers" certainly holds true this year in Southern Ontario, where continuous heavy rainfall over the past few weeks has led to flood watches in various parts of Central and Eastern Ontario due to rising water levels.

Even more rain is expected in the coming days. Rainfall totals over the next few days are predicted to range between 10-20mm, potentially reaching 20-40mm in areas affected by thunderstorms.

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This impending rainfall also carries a risk of severe thunderstorms, particularly on Wednesday in Southwestern Ontario, driven by a surge of warm air that could push temperatures into the 20s in some locales.

This increase in temperature will play a crucial role in the development of severe weather conditions starting Wednesday afternoon. However, this will be primarily localized to Deep Southwestern Ontario, including Windsor, Chatham, and Sarnia, limiting the severe threat to these areas. In contrast, temperatures in Central and Eastern Ontario are expected to struggle to reach double digits.

A line of storms has already started forming in Western Michigan, extending from Grand Rapids to Kalamazoo. This line is anticipated to continue its eastward movement, reaching the Canadian border between 3 to 5 PM.

According to the latest data, conditions seem favourable for these storms to potentially become severe, featuring wind gusts over 100 km/h and large hail, possibly the size of ping-pong balls. The chance of a brief tornado cannot be entirely dismissed.

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Environment Canada has issued a severe thunderstorm watch that notably includes potential tornado risks for the following areas:

  • Chatham-Kent

  • Eastern Lambton County

  • Essex County

  • Komoka

  • Leamington

  • Petrolia

  • Pinery Park

  • Rodney

  • Rondeau Park

  • Sarnia

  • Shedden

  • Strathroy

  • Watford

  • Western Elgin County

  • Western Lambton County

  • Western Middlesex County

  • Windsor

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As the storm line advances towards London and subsequently the Niagara region by early evening, the severe weather threat is expected to wane due to diminishing environmental support. Nevertheless, isolated wind gusts still could reach 90+ km/h, and small to quarter-sized hail remains a possibility.

While Southwestern Ontario and the Greater Toronto Area might experience a few storms later tonight into early Thursday morning, these are likely to be non-severe.

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Flood Watches in Effect for Parts of Central and Eastern Ontario

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The Ministry of Natural Resources and Forestry (MNRF), in collaboration with local conservation authorities, has issued flood watches across various regions in Central and Eastern Ontario this week.

This precaution comes in the wake of recent heavy rainfall and the typical runoff from melting snowpacks in Northern Ontario, which have markedly increased runoff into the area's lakes and rivers.

FLOOD WATCH: potential for flooding exists within specific watercourses and municipalities.

FLOOD WARNING: flooding is imminent or occurring within specific watercourses and municipalities.

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Further rainfall is forecasted for later this week, and according to the MNRF, it may cause water levels in lakes and river flows in some areas to reach or even surpass flood levels.

Areas known to be prone to flooding, especially lower-lying regions, may experience varying degrees of impact as lake and river levels continue to rise following the recent rains. It is advised that residents and visitors remain vigilant when near water bodies and ensure children and pets are closely supervised.

The MNRF also urges extreme caution on forest access roads used for outdoor activities, as these may become temporarily flooded, are susceptible to washouts, and could be impassable due to localized flooding.

Residents in areas historically affected by high water conditions should continue to protect and secure vulnerable properties near watercourses, monitor evolving conditions closely, and stay updated with the latest advisories.

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For more local details, please consult the flood watch for your region:

Information for Northern Ontario and other waterways can be found here.

Late Friday Wind Storm to Give Way to a Snowy Start to the Weekend in Parts of Ontario With Up to 10cm of Snow

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The weather across Southern Ontario has been largely characterized by spring-like conditions, with temperatures soaring into the 20s and the season’s first widespread severe weather event occurring on Tuesday. This pattern continued into Thursday and Friday with heavy rainfall, but a change is on the horizon for the weekend.

Persistent rain across Southern and Northern Ontario on Friday is expected to transition to snow overnight into Saturday morning. For most areas, the snow should melt upon contact, with limited accumulation. However, higher elevations around Georgian Bay and into Northeastern Ontario could see snow accumulations of 5-10cm by Saturday afternoon.

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Before the snow arrives, strong wind gusts are anticipated to develop by Friday afternoon, continuing overnight into Saturday morning.

The strongest gusts, possibly exceeding 90 km/h, are expected along the Lake Huron shoreline and the southeastern shoreline of Georgian Bay.

The hardest hit regions include Kincardine, Goderich, Grand Bend, and Collingwood which could experience wind strong enough to potentially cause damage, including power outages.

In Southwestern Ontario and the Golden Horseshoe, wind gusts are predicted to range from 70 to 90 km/h. Eastern Ontario will see less impact, with wind gusts expected to stay below 70 km/h. The wind is expected to subside by sunrise on Saturday.

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Northeastern Ontario will also experience strong gusts from Friday afternoon into the evening, with the areas directly north of Georgian Bay like Elliot Lake, Manitoulin Island, and Sudbury seeing the strongest gusts, approaching 80-90 km/h.

Widespread gusts of 70-80 km/h are expected in the rest of Northeastern Ontario, with lower gusts further north and west.

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As colder air sweeps into the region overnight, temperatures across Central Ontario and the Dundalk Highlands are likely to hover around the freezing mark into Saturday morning. This will cause the existing rain to transition into wet snow or flurries starting Friday evening.

With temperatures near freezing and recent rainfall, it’s questionable if the snow will stick or accumulate. The best chance for accumulation is in higher elevations such as Shelburne, Orangeville, and the Blue Mountains, where up to 5-10cm of snow could accumulate by Saturday morning.

Surrounding areas extending into Central Ontario, including Barrie, Orillia, Muskoka, and the Kawartha Lakes, might see minor accumulations of 2 to 5cm. This will vary based on local conditions, which could impact the snow's ability to accumulate. Regardless, the area is likely to experience sloppy conditions and icy roads as near-freezing temperatures cause existing rain on roads to freeze and create black ice.

The rest of Southern Ontario will see less than 2cm of snow or no snow at all, as will be the case in Deep Southwestern Ontario, the Golden Horseshoe, and Eastern Ontario.

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Colder temperatures in parts of Northeastern Ontario will allow for better snow accumulation, with areas like Timmins and Cochrane expecting up to 10cm of snow. The rest of Northeastern Ontario, except for regions north of the Georgian Bay shoreline, could see between 5-10cm of snow by Saturday afternoon. Less than 5cm is expected near the Georgian Bay shoreline due to warmer temperatures.

Snowfall is expected to cease across all parts of Ontario by early Saturday afternoon. The weekend will remain chilly for most areas, with temperatures stuck in the single digits on Saturday and Sunday, except in Deep Southwestern Ontario.

Windsor and Chatham may experience a pocket of warmer air, especially on Sunday, with temperatures potentially reaching the 20s and a risk of thunderstorms. The rest of Southern Ontario will see daytime highs in the mid to upper single digits on Sunday.