ONTARIO: Thunderstorm Forecast for Friday, July 21, 2023

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FORECAST DISCUSSION

The risk of non-severe thunderstorms in Eastern Ontario continues into the early morning hours of Friday as the decaying line of storms moves through the region. Additionally, we may see some pop-up storms during the early afternoon in Extreme Eastern Ontario with the highest probability east of Ottawa near the Quebec border. These storms should remain non-severe, although there is a very low chance that one or two of these storms might become marginally severe.

NORTHERN ONTARIO: Thunderstorm Forecast for Friday, July 21, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Friday.

ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023

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FORECAST DISCUSSION

A line of significant storms has developed over Central Michigan this afternoon and is currently tracking toward Southern Ontario. Based on the environment, we have upgraded our forecast to an ‘extreme’ severe risk for Deep Southwestern Ontario. This is our highest threat level and is reserved for events we believe are going to be widespread, destructive, and pose a significant risk to those in the storm's path.

Generally, this level is used in the case of tornado outbreaks or destructive wind events, which, in today's case, is the latter. While the tornado risk is present, it likely won't reach outbreak status - although that can't be ruled out completely.

 
 

The main concern will be an intense line of storms sweeping across Southwestern Ontario during the late afternoon and early evening hours, bringing widespread wind damage stretching from Georgian Bay and southward into Windsor. Additionally, localized pockets of extremely large hail up to tennis ball-sized (that isn't a typo!) are also likely today with these storms.

This line will continue into the Golden Horseshoe and Central Ontario, where the wind damage threat will be quite strong through the evening hours. Thunderstorms will reach Eastern Ontario somewhere around midnight and could bring isolated damaging wind gusts, with the tornado threat becoming less of a concern later in the night.

TIMING of the strongest risk

Southwestern Ontario: 3 - 7 PM

Central Ontario: 4 - 9 PM

Golden Horseshoe: 6 - 10 PM

Eastern Ontario: 10 - 2 AM

TORNADO RISK

The tornado risk for this event is strongest in Southwestern Ontario, from Windsor and up to the Eastern Lake Huron shoreline. This is where we expect to see at least a couple of tornadoes, with a strong long-tracked tornado not out of the question. These tornadoes may spin up quickly without warning and could be rain-wrapped, making them hard to see coming.

One or two tornadoes are possible to the east from the Niagara region and up into Central Ontario. This is mainly for the potential of isolated storms popping up ahead of the main line around Georgian Bay and Lake Simcoe later this afternoon. The tornado threat will diminish later tonight by the time the main line of storms moves through, so we will likely have just an isolated tornado threat with that.

We can’t emphasize enough how serious and dangerous it could get this afternoon into the evening across Southern Ontario. You NEED to ensure you stay aware of the weather today and have a plan in place to seek shelter if severe weather approaches. This will be a very widespread event, so almost everyone will likely see some form of severe weather today. Please stay safe!

ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023

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FORECAST DISCUSSION

Confidence is growing in what could be the strongest severe weather event we've seen thus far across Southern Ontario on Thursday. The most significant area of concern will be along the Lake Huron shoreline and into Deep Southwestern Ontario during the late afternoon into the evening.

Locations like Windsor and Chatham particularly stand out in the data, with the risk of destructive wind gusts and an isolated potential for a strong tornado. Severe potential carries eastward into the GTA and Central Ontario with a slight to isolated severe risk for storms arriving during the evening hours.

A line of strong severe storms is expected to form over Central Michigan just after the lunch hour and slowly track towards our region, reaching Lake Huron by the mid-afternoon. Ahead of this line, we are seeing the potential for isolated storms to pop up around Southwestern Ontario, which could quickly become quite severe with all severe threats possible.

As this line arrives in Southwestern Ontario, widespread destructive wind gusts are expected from Kincardine down into Windsor, with gusts reaching upwards of 90-110 km/h and pockets even higher. As a result, we have put this area in a “significant” severe threat on the map as the wind damage will be widespread.

The line could also feature embedded rotation, leading to a moderate tornado risk. We believe at least one tornado will occur on Thursday somewhere. Hail will also be a threat with locally up to golf ball-sized hail, and more widespread hail ranging from quarter to toonie-sized.

There is some uncertainty as the line tracks further into Ontario towards the evening hours. The data seems to show an environment that could sustain this storm for quite a distance, primarily posing a wind gust threat. It should reach Central Ontario into the GTA sometime around the 8 - 11 PM timeframe, but that could shift depending on the speed of the line. Localized wind gusts here could reach around 100 km/h with up to quarter-size hail, particularly around the Niagara/Hamilton region and Western GTA.

Thunderstorms will continue eastward into Eastern Ontario by the pre-dawn hours, but they should be mostly non-severe. Some models suggest some re-intensification during the morning hours, which could bring a questionable severe threat mainly for strong wind gusts. More on the Friday morning risk will be covered in our forecast for Friday.

TORNADO RISK

The highest tornado risk for this event is expected to be mainly focused on Deep Southwestern Ontario where the environment is capable of supporting rotating storms. These tornadoes may spin up quickly without warning and could be rain-wrapped, making them hard to see coming. A strong tornado can’t be ruled out somewhere in the Windsor, Leamington, Chatham, and Sarnia regions.

One or two tornadoes are possible in much of Southwestern Ontario, including London, Goderich, and Kincardine. There is an isolated tornado threat extending to the Golden Horseshoe and Central Ontario, but this is very conditional based on timing and the strength of the storms once they reach this area. The tornado threat is questionable but still worth including.

Northern Ontario

Isolated thunderstorms could develop around the Georgian Bay shoreline in Northeastern Ontario during the late afternoon and early evening on Thursday. A few of these storms could become marginally severe with threats including 90 km/h wind gusts, up to quarter-sized hail and heavy rainfall. An isolated tornado can’t be ruled out.

NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023

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FORECAST DISCUSSION

Isolated thunderstorms could develop around the Georgian Bay shoreline in Northeastern Ontario during the late afternoon and early evening on Thursday. A few of these storms could become marginally severe with threats including 90 km/h wind gusts, up to quarter-sized hail and heavy rainfall. An isolated tornado can’t be ruled out.

ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023

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FORECAST DISCUSSION

Get ready for what could be the most significant severe risk of the year (so far) in Southern Ontario on Thursday. The current data indicates a strong environment for severe weather, particularly in Southwestern Ontario during the afternoon and evening. As the day progresses, the severe potential will extend eastward into the GTA and Central Ontario, although the severity is expected to decrease the farther you are from Lake Huron.

However, there is a twist in the severe risk—storm development. While we have high confidence in the overall atmospheric conditions, it will rely on storms taking advantage of the energy. Currently, models show isolated storms initiating over Central Michigan in the afternoon and merging into a line of storms over Lake Huron by the early evening as they approach Southwestern Ontario. However, this timing may be too late for daylight heating to sustain these storms, causing them to weaken.

To heighten the severe threat on our side of the border, we need either an earlier arrival of the storm line (which is possible) or the development of isolated cells ahead of it. These storms could bring all severe hazards, including damaging wind gusts, significant hail, and the potential for one or two tornadoes. Otherwise, the later arrival would put more of a focus on damaging wind gusts with hail and tornadoes being lesser of a threat.

Although the overall environment could support a "significant" severe risk, we are currently maintaining a "strong" risk due to this uncertainty. If we gain more confidence in earlier storm development, we may upgrade the forecast. Stay tuned for further updates as we closely monitor the situation.

NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023

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FORECAST DISCUSSION

Strong to severe thunderstorms are possible in Northeastern Ontario on Thursday afternoon and evening. There is a slight risk of severe storms in the southern part of Northeastern Ontario along the Georgian Bay shoreline including Sudbury and North Bay. All severe threats including damaging wind gusts, large hail and even an isolated tornado can’t be ruled out.

ONTARIO: Thunderstorm Forecast for Wednesday, July 19, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Southern Ontario on Wednesday.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, July 19, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Wednesday.

ONTARIO: Thunderstorm Forecast for Tuesday, July 18, 2023

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FORECAST DISCUSSION

Keep an eye out for the potential development of pop-up thunderstorms in Extreme Eastern Ontario, specifically around the Ottawa Valley, during the mid to late afternoon hours on Tuesday. While there is a chance that a few of these storms may become marginally severe, it's important to note that the risk is quite uncertain due to the possibility of limited storm development in the area.

Should these storms materialize, they could bring threats such as up to quarter-sized hail, wind gusts reaching 90 km/h, and localized flash flooding. While the risk is not definite, we believe it's significant enough to warrant an isolated severe risk zone, which includes areas like Ottawa, Smiths Falls, and Cornwall.

The tornado risk remains very low, but it's important to remember that tornadoes can never be completely ruled out.

NORTHERN ONTARIO: Thunderstorm Forecast for Tuesday, July 18, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Tuesday.

ONTARIO: Thunderstorm Forecast for Monday, July 17, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Southern Ontario on Monday.

NORTHERN ONTARIO: Thunderstorm Forecast for Monday, July 17, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Monday.

ONTARIO: Thunderstorm Forecast for Sunday, July 16, 2023

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FORECAST DISCUSSION

Scattered pop-up thunderstorms are expected across Southern Ontario on Sunday, mainly during the afternoon and early evening hours.

Some of these storms have the potential to become marginally severe, with the primary threat being nickel-sized hail, wind gusts up to 90 km/h, and the risk of flash flooding due to the slow-moving nature of these storms.

The most likely area for severe weather is along a corridor stretching from London through Kitchener/Waterloo and into Central Ontario.

While the overall tornado risk is low, there is a possibility of funnel clouds forming with these storms. In rare cases, these funnel clouds may develop into landspout tornadoes.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, July 16, 2023

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FORECAST DISCUSSION

Isolated thunderstorms are expected across Northern Ontario on Sunday, excluding the Far Northwestern region along the Manitoba border. The activity is forecasted to begin during the early afternoon hours around the Thunder Bay region, with isolated storms tracking eastward throughout the day.

There is an isolated severe risk along the Quebec border, including areas such as Englehart, Chapleau, and Elliot Lake during the afternoon and evening. The main threats associated with these storms will be nickel-sized hail and wind gusts reaching speeds of up to 90 km/h.

ONTARIO: Thunderstorm Forecast for Saturday, July 15, 2023

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FORECAST DISCUSSION

Widespread pop-up thunderstorm activity is expected across Southern Ontario on Saturday. Based on the latest data, there is a questionable isolated severe risk associated with these storms, particularly in Central Ontario and the Orangeville, Kitchener/Waterloo, and Woodstock regions.

Most of the storms are anticipated to occur during the afternoon, although some activity may also occur in the morning. The primary severe risk will be during the afternoon storms, which could bring threats including quarter-sized hail, wind gusts reaching 90 km/h, and heavy rainfall.

Additionally, there is a very questionable potential for funnel clouds with these storms, which in rare cases could touch down and become landspout tornadoes.

NORTHERN ONTARIO: Thunderstorm Forecast for Saturday, July 15, 2023

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FORECAST DISCUSSION

Isolated thunderstorms are possible in Northeastern Ontario during the afternoon and evening on Saturday. A few of these storms may reach marginally severe levels with hail up to the size of quarters, 90 km/h wind gusts and heavy rainfall. The strongest risk for severe storms exists along the Quebec border and as far west as the Chapleau region.

NORTHERN ONTARIO: Thunderstorm Forecast for Friday, July 14, 2023

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FORECAST DISCUSSION

A few non-severe thunderstorms are possible around the Thunder Bay region during the afternoon and early evening on Friday.

ONTARIO: Thunderstorm Forecast for Friday, July 14, 2023

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FORECAST DISCUSSION

Scattered thunderstorms are expected to develop across Lake Huron and track into Southwestern Ontario by the late afternoon and evening on Friday. There is some question on exactly how strong these storms will be by the time they reach land as some models show them fizzling out quite fast. If the storms do hold together, they could present an isolated severe threat including 90 km/h wind gusts and quarter-sized hail. An isolated tornado can’t be ruled out but the risk is fairly low.

ONTARIO: Thunderstorm Forecast for Thursday, July 13, 2023

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FORECAST DISCUSSION

Isolated storms are expected to develop in Eastern Ontario and the Ottawa Valley, stretching along the American border on Thursday afternoon. The environment is conducive to severe storms, with all threats including tornadoes on the table.

Based on the latest data, the most significant risk lies along the border and extends into the Cornwall area, east of Ottawa. We have classified this area as a 'strong' severe risk, with the potential for hail up to the size of toonies or ping pong balls, wind gusts exceeding 115 km/h, and the possibility of tornadoes.

Moving westward, the severe risk diminishes rapidly, with Ottawa, Brockville, and Smiths Falls falling into the slight severe risk category. The severity of storms in Kingston is isolated and questionable, considering the expected development to occur just north and east of the city.

Tornado Risk

The anticipated tornado threat on Thursday will be localized to Deep Eastern Ontario, including Morrisburg, Cornwall, and Alexandria. These areas may experience one to two tornadoes, depending on the storm's track. It's important to note that the tornado threat in Eastern Ontario will be influenced by the storm's timing, as some models suggest they may occur just before crossing into Quebec. An isolated tornado threat extends from Ottawa to Gananoque.