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.

NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, July 13, 2023

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FORECAST DISCUSSION

Isolated thunderstorms are possible in Northwestern Ontario during the afternoon and evening on Thursday. Some of these storms could reach marginally severe levels including damaging wind gusts, large hail and heavy rainfall. An isolated tornado can’t be ruled out.

Nocturnal Severe Thunderstorm & Tornado Threat for Southwestern Ontario Late Wednesday

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THUNDERSTORM RISK

Confidence is increasing in the potential for an active and stormy night across Deep Southwestern Ontario on Wednesday. A complex of strong to severe storms is expected to develop over Illinois and Michigan in the late afternoon and evening. These storms carry a significant tornado threat, with the Storm Prediction Center in the US placing the Chicago area under a rare 10% significant tornado threat for today.

The environment appears favourable to support the strong cluster of storms as they track across lower Michigan and reach Deep Southwestern Ontario late in the evening. There may even be some isolated storm development ahead of the main line between 8 - 11 PM around Windsor and Chatham.

Both the isolated storms and the complex of storms later in the evening could bring strong severe threats, including large hail up to the size of ping pong balls, wind gusts of 100-120 km/h, and intense rainfall. The Windsor-Essex region faces the strongest tornado risk.

The severe threat will continue into the early overnight hours after midnight, with an isolated severe risk as far north as Goderich and Kitchener, mainly due to the wind threat. Non-severe nocturnal thunderstorm potential will extend northeastward into the Golden Horseshoe and Central Ontario throughout the overnight hours.

tornado RISK

The window of maximum tornado risk is expected to be between 8 PM and 12 AM, spanning Windsor, Essex, and Leamington. If storms arrive before midnight, there is potential for one or two tornadoes, as even a small trigger could result in a spin-up. Conversely, the tornado risk is lower if storms arrive after midnight.

There is an isolated tornado threat from Sarnia through Strathroy, extending into the London region, primarily during the late evening into the early overnight hours.

fLOODING RISK

Apart from Deep Southwestern Ontario, the main concern associated with these storms will be the potential for flooding overnight and into Thursday morning. Current model data suggests a widespread area from Windsor through London, around Lake Simcoe, and the Petawawa region could receive between 50 to 100mm of rain. Localized areas may even exceed 100mm due to thunderstorm activity.

The flooding risk will be isolated and dependent on the track of this cluster of storms. The provided map gives a rough indication of where the heaviest rainfall is anticipated, but the exact track may shift west or east, affecting overall rainfall totals. It is important to be prepared for significant overnight rainfall occurring within a short timeframe.

ONTARIO: Thunderstorm Forecast for Wednesday, July 12, 2023

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FORECAST DISCUSSION

Strong to severe thunderstorms are anticipated to develop over Central Michigan on Wednesday, potentially impacting Deep Southwestern Ontario during the late evening hours.

Although the storms are expected to weaken as they approach the border between 9-11 PM, there remains a possibility for isolated storms to reach marginal severe levels, especially in the Windsor and Chatham regions. The primary threat would be strong wind gusts. Additionally, there is a questionable isolated tornado risk associated with these storms.

Non-severe nocturnal thunderstorm potential will carry eastward into the rest of Southwestern Ontario and into the Golden Horseshoe throughout the overnight hours.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, July 12, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Wednesday.

ONTARIO: Thunderstorm Forecast for Tuesday, July 11, 2023

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FORECAST DISCUSSION

A widespread risk of thunderstorms is expected across Southern Ontario on Tuesday. This includes a slight risk of severe storms along the Lake Huron shoreline and into the Collingwood/Barrie region during the mid to late afternoon hours. Storm development is anticipated after the lunch hour, with isolated storms originating from Lake Huron and tracking into Southwestern and Central Ontario.

The primary concern lies along the Kincardine, Collingwood, and Barrie corridor. As these storms move through the region, there is a potential for a brief tornado. Large hail and strong wind gusts are also possible with these storms.

Further south, strong storm development is expected over Lake Huron in the mid-afternoon (2-4 PM) as they make landfall from Sarnia through Grand Bend and into Goderich. The environment these storms will encounter has the potential for significant hail, up to the size of toonies or even golf balls, along with wind gusts of 100 km/h. There is also a tornado risk, particularly as these storms reach their peak strength upon landfall.

By the later afternoon, the previously isolated storms are expected to merge into a long line of storms extending from Barrie southward to London. This line will primarily bring a threat of damaging wind gusts ranging from 90-100 km/h, with quarter-sized hail and a risk of flash flooding. Isolated pop-up storms are also possible throughout Central Ontario and into the Ottawa Valley, although no organized activity is expected. These storms could still produce large hail and damaging wind gusts.

TORNADO RISK

The focus of the tornado risk will be along the Lake Huron and southern Georgian Bay shorelines. Given the environment and timing, there is a decent chance of seeing at least one tornado somewhere in the Sarnia, Grand Bend, Goderich, and Kincardine region. Timing is crucial, as these events have previously started earlier than expected before daylight heating fully primes the environment for maximum severe potential.

An isolated tornado risk extends from southwestern Ontario through much of Central Ontario and into the Ottawa Valley. While the Golden Horseshoe may experience marginally severe storms, the line of storms is expected to have less energy upon reaching the area. Therefore, the primary threat will be damaging winds, with minimal risk of tornadoes.

NORTHERN ONTARIO: Thunderstorm Forecast for Tuesday, July 11, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Tuesday.

ONTARIO: Thunderstorm Forecast for Tuesday, July 11, 2023

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FORECAST DISCUSSION

Widespread thunderstorm activity is expected across Southern Ontario during the afternoon on Tuesday. Some of these storms may become severe with all threat types possible (hail, wind, flooding and tornado). Confidence is low in the exact severity and location so we’re sticking with an isolated risk for now. An upgrade to a ‘slight’ or even ‘strong’ risk isn’t out of the question once we get closer to Tuesday. An updated forecast will be issued sometime on Monday.

ONTARIO: Thunderstorm Forecast for Monday, July 10, 2023

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FORECAST DISCUSSION

Heavy rain associated with a slow-moving system along the Northeastern US is expected to affect Deep Eastern Ontario throughout the day on Monday. The main threat will be heavy rainfall with localized totals between 25-50mm possible. Additionally, there is the risk of non-severe thunderstorms embedded within this area of precipitation.

NORTHERN ONTARIO: Thunderstorm Forecast for Monday, July 10, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Monday.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, July 9, 2023

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FORECAST DISCUSSION

Widespread thunderstorm activity is expected across Northwestern Ontario during the afternoon and early evening on Sunday. Based on the latest data, we believe the environment will be favourable for these storms to become quite strong with threats including up to golf ball-sized hail and wind gusts in excess of 100km/h. One or two tornadoes are also possible with the strongest risk around the Dryden, Sioux Lookout and Armstrong region.

ONTARIO: Thunderstorm Forecast for Sunday, July 9, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Southern Ontario on Sunday.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, July 9, 2023

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FORECAST DISCUSSION

Widespread thunderstorm activity is expected across Northwestern Ontario during the afternoon and early evening on Sunday. A few of these storms may reach severe levels with up to quarter-sized hail, 90 km/h wind gusts and heavy rainfall. An isolated tornado can’t be ruled out.

ONTARIO: Thunderstorm Forecast for Saturday, July 8, 2023

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FORECAST DISCUSSION

There is the risk of non-severe thunderstorms in Deep Southwestern Ontario extending into regions east of Lake Huron. Thunderstorms are expected to develop over Michigan and may cross into Ontario sometime during the afternoon and early evening on Saturday. These storms should be fairly weak, however, there is a very questionable risk for strong storms toward the Windsor, Sarnia and Chatham regions.

The strongest environment for severe activity is expected to remain south of the border, but it isn’t out of the question that one of these storms sneak across the border. Although the confidence is too low for us to introduce an isolated severe risk.

NORTHERN ONTARIO: Thunderstorm Forecast for Saturday, July 8, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Saturday.

ONTARIO: Thunderstorm Forecast for Friday, July 7, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Southern Ontario on Friday.