ONTARIO: Thunderstorm Forecast for Thursday, August 10, 2023

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As we look ahead to Thursday, there's a growing risk of severe thunderstorms, and we have made some important changes to our forecast. Here's what you need to know:

We've updated our thunderstorm risk forecast to include a 'strong' chance of severe storms, covering a large area from Lake Huron through Lake Simcoe and extending into parts of the Ottawa Valley. Also, Central and Eastern Ontario, including the Greater Toronto Area (GTA), are now under a 'slight' risk. This means we're seeing the potential for stronger storms than previously thought, especially in those areas.

The timing of storm development has shifted a bit. We expect isolated storms to kick off sometime between 11 am and 2 pm. These storms are likely to pop up around Owen Sound and Georgian Bay before moving inland during the early afternoon.

The environment is favourable for some of these storms to become supercells around Lake Simcoe and south of Georgian Bay. These storms have the potential to bring threats including hail up to the size of golf balls and damaging wind gusts reaching up to 110 km/h. We could also see one or two tornadoes if these storms manage to get rotating which the environment could support.

As the day goes on, the focus of the storm threat will shift eastward. Isolated storms will come together to form a line of storms. We may even see a few isolated supercells ahead of the main line throughout the Ottawa Valley which would present a buffet of storm threats including large hail, destructive wind gusts and tornadoes. Throughout this line of storms, the main worry is strong winds that could cause damage. But, we can't ignore the possibility of large hail and a few isolated tornadoes either.

We're also keeping an eye on Southwestern Ontario, where we could see isolated storms forming off Lake Huron. This might affect places like Goderich and Kitchener-Waterloo, but it's a bit uncertain at the moment.

By the late afternoon, the severe weather risk should start to decrease from west to east.

NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, August 10, 2023

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Thunderstorms are currently not expected across Northern Ontario on Thursday.

ONTARIO: Thunderstorm Forecast for Thursday, August 10, 2023

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Prepare for a resurgence of thunderstorm activity across Southern Ontario on Thursday. This will be accompanied by an isolated severe threat spanning from Southwestern Ontario through the Golden Horseshoe and extending into Eastern Ontario. Our attention is focused on two distinct areas of storm development in Southern Ontario.

Firstly, storms are anticipated to originate over Lake Huron, tracking into the Greater Toronto Area (GTA) and Niagara region. Simultaneously, another zone of storm development is anticipated, ranging from Lake Simcoe up to Renfrew. These storms are projected to commence during the early afternoon hours and advance eastward throughout the day.

While these storms are not expected to be widespread, they possess the potential to reach marginally severe levels, accompanied by wind gusts of up to 90 km/h, hail reaching the size of quarters, and substantial rainfall. Additionally, there exists a chance of isolated tornado activity.

The precise timing of these storm formations introduces an element of uncertainty that could influence the overall storm threat. Delayed storm initiation would elevate the severity threat, as increased daylight heating would contribute to heightened energy levels. Conversely, some models indicate the potential for initiation further east, possibly even outside of Ontario.

Currently, we are sticking with an isolated severe threat. It is crucial to note that not all regions within the severe risk area will experience storm activity on Thursday. Any storm occurrence will be localized, impacting a limited area.

In our upcoming Wednesday evening update, we might consider introducing a more localized 'slight' severe risk zone if the environmental conditions indicate a stronger potential than initially anticipated.

ONTARIO: Thunderstorm Forecast for Wednesday, August 9, 2023

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Thunderstorms are currently not expected across Southern Ontario on Wednesday.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, August 9, 2023

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Expect scattered thunderstorms to impact much of Northeastern Ontario during the afternoon and early evening on Wednesday. The atmospheric conditions are conducive for a few of these storms to escalate to severe levels, with a particular focus on the area around Elliot Lake and Sault Ste. Marie.

Current indications point towards the possibility of one or two discrete supercells forming within this region between 1-4 PM. These storms could carry slight severe threats, including hail up to the size of ping pong balls, wind gusts reaching speeds of 100 km/h, and a potential for an isolated tornado.

Moving further across Northeastern Ontario, extending along the Quebec border, there is an isolated risk of severe weather. While some storms might only reach marginally severe levels, it's important to note that we can't entirely dismiss the possibility of stronger storms, including the potential for tornadoes, anywhere in Northeastern Ontario.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, August 9, 2023

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Thunderstorm activity is expected to develop in Northeastern Ontario during the day on Wednesday. It appears that the environment will be favourable for some of these storms to approach marginally severe levels, especially along the Quebec border. All severe threats including an isolated tornado risk are on the table. We will have a more detailed forecast on Tuesday evening.

ONTARIO: Thunderstorm Forecast for Tuesday, August 8, 2023

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Thunderstorms are currently not expected across Southern Ontario on Tuesday.

NORTHERN ONTARIO: Thunderstorm Forecast for Tuesday, August 8, 2023

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There is a slight risk of severe thunderstorms in Northwestern Ontario during the afternoon and early evening on Tuesday. Isolated storms are expected to develop stretching from Fort Frances through Dryden and into Far Northwestern Ontario. These discreet cells will have the potential to bring severe threats including hail up to the size of ping pong balls, 100 km/h wind gusts and heavy rainfall. An isolated tornado can’t be ruled out.

ONTARIO: Thunderstorm Forecast for Monday, August 7, 2023

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Starting early Monday afternoon, scattered thunderstorm activity could bring the risk of severe weather to parts of Southern Ontario. The Golden Horseshoe and Eastern Ontario regions are particularly susceptible to storm development, with potential threats including heavy rainfall, strong wind gusts, and small hail.

A slight risk of severe weather is in place for the Niagara region, extending into Eastern Ontario along the Lake Ontario shoreline, including areas like Peterborough and Kingston. The primary concerns in these areas are hail up to the size of quarters and wind gusts reaching 90-100 km/h. Additionally, although unlikely, an isolated tornado can't be entirely ruled out.

For the rest of Eastern Ontario and along the Golden Horseshoe, there is an isolated severe threat. However, storm development further to the west is more questionable, potentially limiting the actual impact in these areas.

Moreover, heavy rainfall will be a significant concern with these storms, potentially leading to localized flooding. For more detailed information on the flooding threat, please refer to our dedicated rainfall forecast available here:

NORTHERN ONTARIO: Thunderstorm Forecast for Monday, August 7, 2023

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Thunderstorms are currently not expected across Northern Ontario on Monday.

Multiple Waves of Heavy Rainfall in Southern Ontario With Up to 40–80mm of Rain Possible by Tuesday

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The start of August has been marked by a wet trend in parts of Southern Ontario, and it looks like the pattern will persist as we enter the first full week of the month. Some of the heaviest rainfall totals are expected to affect the same areas that saw flash flooding last week. Those in the Lindsay area saw rainfall totals approaching 100mm!

And we are currently forecasting an additional 30-60mm of rain over the next few days for the same area. Anticipate several waves of precipitation moving across Southern Ontario starting Sunday afternoon and extending through Monday into Tuesday. The heavy rainfall will be accompanied by embedded thunderstorm activity, intensifying the overall rainfall totals.

The first wave has already begun to sweep through Southwestern Ontario as of Sunday mid-afternoon, expected to persist through the evening and overnight. The most substantial and prolonged rainfall will be centred off-shore over Lake Huron, but areas close to the shoreline and the Bruce Peninsula may also be affected.

Residents in the Golden Horseshoe should anticipate on-and-off rain beginning around the dinner hour on Sunday, with the intensity increasing after midnight, bringing the possibility of isolated non-severe thunderstorms. By early Monday morning, this precipitation will move into Central and Eastern Ontario.

There will be a temporary break in the rain for Southwestern Ontario by morning and for Eastern Ontario around noon on Monday. The timing of this lull between the two waves is crucial, as it will determine the potential for severe weather risk later in the day.

Some indications suggest the development of an environment conducive to supporting marginally severe storms during Monday afternoon and evening. The Golden Horseshoe and Eastern Ontario regions are particularly favourable for storm development, posing threats of heavy rainfall, strong wind gusts, and small hail.

A primary concern lies in the potential for flash flooding, as these storms may persist and bring extensive rainfall totals exceeding 100mm. Additionally, hail up to the size of nickels and wind gusts reaching 80-90 km/h are possible threats. Although the tornado risk is expected to be minimal, it can't be entirely ruled out.

Based on the latest data, we are also considering the possibility of adding a slight risk zone stretching from Lake Simcoe to Kingston, as we gain confidence in the potential for wind gusts of up to 100 km/h within these storms. An updated thunderstorm forecast will be posted late Sunday evening after reviewing the evening model data.

This storm risk will contribute to additional rainfall over the next 48 hours, with heavy rain expected late Monday and continuing into the early part of Tuesday in Eastern Ontario. The precipitation should finally clear out by the afternoon on Tuesday.

Overall, widespread rainfall totals over the next two days are projected to range from 20 to 60mm, with higher amounts in Eastern and Central Ontario due to the thunderstorm threat. Some models even suggest that a localized pocket around the Kingston region could receive in excess of 100mm by Tuesday afternoon.

Multiple Waves of Heavy Rainfall in Southern Ontario With Up to 40–80mm of Rain Possible by Tuesday

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The start of August has been marked by a wet trend in parts of Southern Ontario, and it looks like the pattern will persist as we enter the first full week of the month. Some of the heaviest rainfall totals are expected to affect the same areas that saw flash flooding last week. Those in the Lindsay area saw rainfall totals approaching 100mm!

And we are currently forecasting an additional 30-60mm of rain over the next few days for the same area. Anticipate several waves of precipitation moving across Southern Ontario starting Sunday afternoon and extending through Monday into Tuesday. The heavy rainfall will be accompanied by embedded thunderstorm activity, intensifying the overall rainfall totals.

The first wave has already begun to sweep through Southwestern Ontario as of Sunday mid-afternoon, expected to persist through the evening and overnight. The most substantial and prolonged rainfall will be centred off-shore over Lake Huron, but areas close to the shoreline and the Bruce Peninsula may also be affected.

Residents in the Golden Horseshoe should anticipate on-and-off rain beginning around the dinner hour on Sunday, with the intensity increasing after midnight, bringing the possibility of isolated non-severe thunderstorms. By early Monday morning, this precipitation will move into Central and Eastern Ontario.

There will be a temporary break in the rain for Southwestern Ontario by morning and for Eastern Ontario around noon on Monday. The timing of this lull between the two waves is crucial, as it will determine the potential for severe weather risk later in the day.

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ONTARIO: Thunderstorm Forecast for Friday, September 1, 2023
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This storm risk will contribute to additional rainfall over the next 48 hours, with heavy rain expected late Monday and continuing into the early part of Tuesday in Eastern Ontario. The precipitation should finally clear out by the afternoon on Tuesday.

Overall, widespread rainfall totals over the next two days are projected to range from 20 to 60mm, with higher amounts in Eastern and Central Ontario due to the thunderstorm threat. Some models even suggest that a localized pocket around the Kingston region could receive in excess of 100mm by Tuesday afternoon.

ONTARIO: Thunderstorm Forecast for Monday, August 7, 2023

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Beginning early Monday morning and persisting throughout the day, Southern Ontario is expected to be impacted by heavy rainfall. The rainfall could be accompanied by embedded thunderstorms, with most of these storms likely to remain non-severe. However, there are indications that a few of these storms could escalate to marginally severe levels during the afternoon and evening.

The Golden Horseshoe and Eastern Ontario regions are particularly favourable for storm development that could result in heavy rainfall, strong wind gusts, and small hail. The primary concern lies in the potential for flash flooding, as these storms may be persistent and bring extensive rainfall totals exceeding 100mm. Additionally, hail up to the size of nickels and wind gusts reaching 80-90 km/h are also possible threats. Although the tornado risk is expected to be minimal, it can't be entirely ruled out.

The forecast does come with some uncertainty regarding storm development later in the day, which will significantly influence the actual threat to our region. Therefore, it's essential to keep a close eye on our updated forecast, which will be released Sunday evening.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, August 6, 2023

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Thunderstorms are currently not expected across Northern Ontario on Sunday.

ONTARIO: Thunderstorm Forecast for Sunday, August 6, 2023

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Thunderstorms are currently not expected across Southern Ontario on Sunday.

ONTARIO: Thunderstorm Forecast for Saturday, August 5, 2023

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Thunderstorms are currently not expected across Southern Ontario on Saturday.

NORTHERN ONTARIO: Thunderstorm Forecast for Saturday, August 5, 2023

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Thunderstorms are currently not expected across Northern Ontario on Saturday.

ONTARIO: Thunderstorm Forecast for Friday, August 4, 2023

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Thunderstorms are currently not expected across Southern Ontario on Friday.

NORTHERN ONTARIO: Thunderstorm Forecast for Friday, August 4, 2023

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Thunderstorms are currently not expected across Northern Ontario on Friday.

ONTARIO: Thunderstorm Forecast for Thursday, August 3, 2023

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Central and Eastern Ontario are in the bullseye for a strong risk of severe weather on Thursday. Isolated supercells are anticipated to develop somewhere in the vicinity of North Bay, extending into Algonquin Park during the early afternoon. These storms are projected to track southeastward, impacting regions such as Bancroft, Pembroke, Renfrew, and the Ottawa Valley later in the afternoon and early evening.

As time progresses, a transition from discrete storms to a more consolidated cluster is expected. Storm threats will include hail up to the size of golf balls and destructive wind gusts, potentially reaching 110 km/h. With the environment favouring rotating storms, there is a possibility of one or two tornadoes occurring.

The storm threat will persist as it reaches the Brockville and Kingston region, with the mature line of storms expected to affect these areas around 8-10 PM. During this time, the primary concern will shift to strong wind gusts, though tornadoes will still be possible.

Another risk zone has our focus around the Lake Huron shoreline, where isolated storms may develop over the lake during the late afternoon. These storms could subsequently track onshore, carrying the risk of severe weather, including hail up to the size of ping pong balls, 100 km/h wind gusts, and the potential for one or two tornadoes. However, this area has a lower level of confidence in its forecast, as storm development may not occur or may happen later than expected.

In the extreme southern portion of Northeastern Ontario, including North Bay, a strong severe risk is in place. Storms are projected to initiate here before tracking into Eastern Ontario during the early afternoon hours. A slight severe risk also extends into Sudbury and along the Georgian Bay shoreline, where a line of storms may form before traversing over Lake Huron. Both of these areas carry a favourable environment for large hail, strong wind gusts, and the possibility of an isolated tornado.