NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, August 3, 2023

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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.

ONTARIO: Thunderstorm Forecast for Thursday, August 3, 2023

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Weather conditions in Southern Ontario are set to take a potentially severe turn on Thursday, with a strong threat of severe weather expected for Central and Eastern Ontario. Current model guidance suggests the development of an explosive weather environment stretching from Muskoka to the Ottawa Valley, with possible storm initiation during the afternoon and early evening.

However, uncertainties linger about the precise location and timing of these storms. While Central Ontario may experience limited storm activity, confidence is higher for the Ottawa Valley, where a few supercells could form, bringing threats of large hail, damaging wind gusts, and heavy rainfall.

Of particular concern is the tornado risk, which could be strong with these storms. Regions such as Pembroke through Renfrew and into the Ottawa area have the highest tornado risk. The potential for one or two tornadoes can't be ruled out in these areas.

Moving southward, storm activity is also possible over Lake Huron, extending into areas east of the lake, including Kincardine and Goderich. While these storms may not have as favourable environmental conditions, they could still reach marginally severe levels. An isolated tornado risk also exists in this region. We will closely monitor the evolving environment, and based on the data, we may need to expand the 'slight' risk to encompass this area.

We will issue an updated forecast late Wednesday evening once we have thoroughly assessed the latest data.

ONTARIO: Thunderstorm Forecast for Wednesday, August 2, 2023

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As Wednesday evening approaches, isolated thunderstorm activity is expected to develop over Georgian Bay and Lake Huron. The time frame for these storms is from 7 PM to 12 AM. These storms will then track across the Bruce Peninsula and into the Simcoe County and Muskoka region.

While the overall severe threat is expected to be limited due to the later timing of the storms, there is the potential for a few of them to reach marginally severe levels. Within these storms, we could experience wind gusts of up to 90 km/h, hail up to the size of nickels, and heavy rainfall.

One aspect that warrants attention is an isolated tornado risk. Though not a significant concern, models indicate that any storms developing in this area could pose a slight tornado risk.

Decoding Thunderstorm Forecasts: Threats Over Probability ⚡️🌩️

When it comes to thunderstorm forecasts, there are two distinct approaches:

  • Forecasting the probability of thunderstorms occurring based on storm development.

  • Forecasting the potential thunderstorm threats based on the environment.

Both methods have their merits, but at Instant Weather, we prioritize focusing on the threats rather than just the probability. After all, it's the possible threats that pose a real danger to you.

We achieve this by carefully evaluating the latest model data and assessing the level of threat posed by each type should storms develop in a particular region. This includes the risk of tornadoes, damaging winds, large hail, and flooding.

Our overall severe risk classification comprises 6 categories: non-severe, isolated, slight, strong, significant, and extreme. The final category is determined based on the maximum threat level among all the individual threat types.

The graphic above highlights the risk levels of each threat type and their correlation with the overall severe risk. Minor regional differences exist between Ontario and the Prairies; for example, tennis ball-sized hail is classified as a 'strong' risk in the Prairies, while in Ontario, it's considered 'significant'. This variation results from the higher frequency of large hail occurrences in the Prairies compared to Ontario.

Please note that our forecast map doesn’t focus on probabilities, so we don't guarantee storms for a specific region.

In fact, most locations within a region may not experience a single storm. The localized nature of storm development makes it challenging to predict. Instead, we aim to inform you about the potential threats IF storms develop in a given area, based on the surrounding environment.

For a comprehensive understanding of how widespread an event could be and the potential for a ‘bust’, we encourage you to read the entire forecast discussion.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, August 2, 2023

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Widespread thunderstorms are on the horizon for much of Northern Ontario on Wednesday, bringing with them the potential for severe weather. A potent environment will set the stage for any storms that develop to become severe, with threats including hail up to the size of golf balls, 100 km/h wind gusts, and flash flooding. The timeline for storms will span from the afternoon into the evening hours, with the peak intensity expected between 4 PM and 9 PM.

In the central part of Northern Ontario, just north of Thunder Bay, we have a 'strong' risk forecasted due to the threat of supercells. These supercells may produce very large hail, strong wind gusts, and the possibility of an isolated tornado. The tornado risk is strongest in Northeastern Ontario near the Quebec border, where we could see one or two tornadoes. However, the hail and wind threats in this area are somewhat lower, leading to a 'slight' risk classification.

Decoding Thunderstorm Forecasts: Threats Over Probability ⚡️🌩️

When it comes to thunderstorm forecasts, there are two distinct approaches:

  • Forecasting the probability of thunderstorms occurring based on storm development.

  • Forecasting the potential thunderstorm threats based on the environment.

Both methods have their merits, but at Instant Weather, we prioritize focusing on the threats rather than just the probability. After all, it's the possible threats that pose a real danger to you.

We achieve this by carefully evaluating the latest model data and assessing the level of threat posed by each type should storms develop in a particular region. This includes the risk of tornadoes, damaging winds, large hail, and flooding.

Our overall severe risk classification comprises 6 categories: non-severe, isolated, slight, strong, significant, and extreme. The final category is determined based on the maximum threat level among all the individual threat types.

The graphic above highlights the risk levels of each threat type and their correlation with the overall severe risk. Minor regional differences exist between Ontario and the Prairies; for example, tennis ball-sized hail is classified as a 'strong' risk in the Prairies, while in Ontario, it's considered 'significant'. This variation results from the higher frequency of large hail occurrences in the Prairies compared to Ontario.

Please note that our forecast map doesn’t focus on probabilities, so we don't guarantee storms for a specific region.

In fact, most locations within a region may not experience a single storm. The localized nature of storm development makes it challenging to predict. Instead, we aim to inform you about the potential threats IF storms develop in a given area, based on the surrounding environment.

For a comprehensive understanding of how widespread an event could be and the potential for a ‘bust’, we encourage you to read the entire forecast discussion.

ONTARIO: Thunderstorm Forecast for Tuesday, August 1, 2023

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Thunderstorms are currently not expected across Southern Ontario on Tuesday.

Decoding Thunderstorm Forecasts: Threats Over Probability ⚡️🌩️

When it comes to thunderstorm forecasts, there are two distinct approaches:

  • Forecasting the probability of thunderstorms occurring based on storm development.

  • Forecasting the potential thunderstorm threats based on the environment.

Both methods have their merits, but at Instant Weather, we prioritize focusing on the threats rather than just the probability. After all, it's the possible threats that pose a real danger to you.

We achieve this by carefully evaluating the latest model data and assessing the level of threat posed by each type should storms develop in a particular region. This includes the risk of tornadoes, damaging winds, large hail, and flooding.

Our overall severe risk classification comprises 6 categories: non-severe, isolated, slight, strong, significant, and extreme. The final category is determined based on the maximum threat level among all the individual threat types.

The graphic above highlights the risk levels of each threat type and their correlation with the overall severe risk. Minor regional differences exist between Ontario and the Prairies; for example, tennis ball-sized hail is classified as a 'strong' risk in the Prairies, while in Ontario, it's considered 'significant'. This variation results from the higher frequency of large hail occurrences in the Prairies compared to Ontario.

Please note that our forecast map doesn’t focus on probabilities, so we don't guarantee storms for a specific region.

In fact, most locations within a region may not experience a single storm. The localized nature of storm development makes it challenging to predict. Instead, we aim to inform you about the potential threats IF storms develop in a given area, based on the surrounding environment.

For a comprehensive understanding of how widespread an event could be and the potential for a ‘bust’, we encourage you to read the entire forecast discussion.

NORTHERN ONTARIO: Thunderstorm Forecast for Tuesday, August 1, 2023

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A line of strong thunderstorms is expected to develop over Manitoba during the early morning hours on Tuesday. This line will cross into Northwestern Ontario by the late morning or early afternoon. Although the environment is quite weak this early in the day, we belive the line could feature marginally severe storms. The main threats will be 90 km/h wind gusts, hail up to the size of quarters and heavy rainfall.

Storms will move south of the border by the late afternoon.

Decoding Thunderstorm Forecasts: Threats Over Probability ⚡️🌩️

When it comes to thunderstorm forecasts, there are two distinct approaches:

  • Forecasting the probability of thunderstorms occurring based on storm development.

  • Forecasting the potential thunderstorm threats based on the environment.

Both methods have their merits, but at Instant Weather, we prioritize focusing on the threats rather than just the probability. After all, it's the possible threats that pose a real danger to you.

We achieve this by carefully evaluating the latest model data and assessing the level of threat posed by each type should storms develop in a particular region. This includes the risk of tornadoes, damaging winds, large hail, and flooding.

Our overall severe risk classification comprises 6 categories: non-severe, isolated, slight, strong, significant, and extreme. The final category is determined based on the maximum threat level among all the individual threat types.

The graphic above highlights the risk levels of each threat type and their correlation with the overall severe risk. Minor regional differences exist between Ontario and the Prairies; for example, tennis ball-sized hail is classified as a 'strong' risk in the Prairies, while in Ontario, it's considered 'significant'. This variation results from the higher frequency of large hail occurrences in the Prairies compared to Ontario.

Please note that our forecast map doesn’t focus on probabilities, so we don't guarantee storms for a specific region.

In fact, most locations within a region may not experience a single storm. The localized nature of storm development makes it challenging to predict. Instead, we aim to inform you about the potential threats IF storms develop in a given area, based on the surrounding environment.

For a comprehensive understanding of how widespread an event could be and the potential for a ‘bust’, we encourage you to read the entire forecast discussion.

ONTARIO: Thunderstorm Forecast for Monday, July 31, 2023

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Thunderstorms are currently not expected across Southern Ontario on Monday.

NORTHERN ONTARIO: Thunderstorm Forecast for Monday, July 31, 2023

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Thunderstorms are currently not expected across Northern Ontario on Monday.

ONTARIO: Thunderstorm Forecast for Sunday, July 30, 2023

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Thunderstorms are currently not expected across Southern Ontario on Sunday.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, July 30, 2023

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There is an isolated risk of severe weather in Northern Ontario on Sunday afternoon into the evening hours. The risk zone stretches from Temiskaming Shores through Chapleau, Wawa and into Armstrong. Several isolated storms are expected to develop and will eventually merge into a line of storms later in the day. These storms could present severe risks including toonie-sized hail, 90 km/h wind gusts and heavy rainfall. An isolated tornado can’t be ruled out.

ONTARIO: Thunderstorm Forecast for Saturday, July 29, 2023

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Non-severe thunderstorms are possible across Southwestern Ontario and into the Golden Horseshoe on Saturday. This risk is primarily during the morning and early afternoon with it diminishing later in the day.

NORTHERN ONTARIO: Thunderstorm Forecast for Saturday, July 29, 2023

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Thunderstorms are currently not expected across Northern Ontario on Saturday.

ONTARIO: Thunderstorm Forecast for Friday, July 28, 2023

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FORECAST DISCUSSION

After a brief respite from the stormy skies on Thursday, we're closely monitoring the reemergence of severe thunderstorms for parts of Southwestern, Central and Eastern Ontario on Friday.

Central and Eastern Ontario, particularly the Ottawa Valley, will take the early spotlight as the afternoon and early evening present the perfect environment for isolated supercells. The exact location of storm initiation is unclear but could start as far west as Muskoka and Simcoe County by the early afternoon.

These storms will continue to track eastwards into Eastern Ontario where the environment is only expected to get stronger throughout the day. In light of this, we've gone with a 'significant' severe risk, encompassing Renfrew, Ottawa, and the eastern regions like Cornwall. Our main concern is the potential for an isolated strong tornado due to the potent atmospheric conditions. Additionally, large hail up to the size of golf balls and wind gusts surpassing 100 km/h are other possible threats.

Keep in mind that the risk in Central and Eastern Ontario will be very isolated. We anticipate only a few scattered storms, with most locations within our severe risk forecast likely remaining untouched. As always, the actual risk hinges on storm development taking advantage of the expected environmental factors.

Meanwhile, Southwestern Ontario remains a key area of focus, echoing the recurring pattern of strong severe thunderstorm risks over the past weeks. Models indicate the potential for yet another widespread damaging wind threat, originating from Michigan and crossing into our region. The timing, as always, holds the key to the actual risk on our side of the border.

Earlier in the evening, around dinner time, there are signs of a few isolated storms popping up over Lake Huron and southward into Sarnia and Windsor. These initial storms could present all severe hazards, ranging from hail up to ping pong ball-sized, 100 km/h wind gusts, and one or two tornadoes.

As the night progresses, a mature line of strong to severe storms is expected to impact Deep Southwestern Ontario between 10 PM to 1 AM. The strength of this squall line remains uncertain due to the event's timing, though it does appear more likely to pose a damaging wind gust threat, with localized pockets potentially reaching 110-115 km/h. Additionally, an isolated tornado can't be ruled out.

Further northward development ahead of the line could bring an isolated severe threat to areas around Kincardine and Lake Simcoe during the evening hours. As the line of storms tracks eastward along Lake Erie, it will impact the GTA with the potential for severe wind gusts lingering past midnight.

Localized flash flooding could also be an issue in both Eastern and Southwestern Ontario. This is because we expected rainfall totals could potentially exceed 100mm in localized areas that see multiple rounds of storms.

NORTHERN ONTARIO: Thunderstorm Forecast for Friday, July 28, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on Friday.

ONTARIO: Thunderstorm Forecast for Thursday, July 27, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Southern Ontario on Thursday.

NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, July 27, 2023

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FORECAST DISCUSSION

Thunderstorms are currently not expected across Northern Ontario on DAY.

ONTARIO: Thunderstorm Forecast for Wednesday, July 26, 2023

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FORECAST DISCUSSION

A striking sense of déjà vu sweeps over Southwestern Ontario as we face yet another significant severe threat on Wednesday. While this severe risk differs from last week's ‘extreme’ severe risk and will likely be a lot weaker, it could still pack a punch. The hail risk appears less prominent this time, with expected sizes ranging from toonie to ping pong balls, a departure from the baseball-sized hail we saw on Thursday. However, the tornado risk could be similar to last week with an isolated strong tornado risk. Widespread destructive wind gusts are also possible, and models suggest the potential for severe winds extending eastward into the GTA and Niagara region through the evening.

Our localized 'significant' risk target focuses on the Windsor, Leamington, and Chatham regions. An explosive environment combined with storms forming during the dinner hour heightens the danger. Yet, some model discrepancies in storm mode and timing add an air of uncertainty. If the storms appear earlier, they will have a stronger environment to work with while a later arrival would lessen the threat. It looks like a strong squall line of storms will develop over Michigan and track into Southwestern Ontario sometime between 6 - 10 PM.

It’s important to note that there are hints of a potential ‘bust’ with some models showing storms not developing at all or arriving way too late. This forecast is conditional on storm development. We can say the environment is capable to produce these storm threats but it requires a storm to realize these threats. We are hoping that storms don’t develop as this could get quite nasty if they do show up!

🔴 Significant Severe Risk for Deep Southwestern Ontario (Windsor, Leamington, Chatham):

  • 115 km/h wind gusts

  • Hail up to the size of ping pong balls

  • Isolated strong tornado risk

  • Severe threat starts as early as 5 PM and grows by the hour before peaking around 7 - 10 PM. It should diminish by midnight.

🟠 Strong Severe Risk for the Rest of Southwestern Ontario (Sarnia, London, Lake Huron shoreline):

  • 100 km/h wind gusts

  • Hail up to the size of toonies

  • One or two tornadoes

  • Severe threat starts as early as 5 PM and grows by the hour before peaking around 8 - 11 PM. It should diminish by midnight.

As with last week, the extent of storm progression into Ontario remains uncertain, contingent on timing. Nonetheless, the Kitchener-Waterloo, Greater Toronto and Hamilton Area, and Niagara region might face a severe threat later in the evening. At this point, the primary concern will be damaging wind gusts, with tornado and hail risks slightly diminished but not entirely out of the question.

Isolated storms are also possible this afternoon and evening across Central and Eastern Ontario. We have extended the isolated severe risk into this region to account for the pop-up storms possible later in the day.

Moreover, we have serious concerns over flash flooding potential. Model projections indicate some areas might encounter multiple rounds of thunderstorms within a 6-12 hour window, leading to localized rainfall totals exceeding 100mm, possibly even reaching 150-200mm. While not all areas will experience such deluge, urban centers prone to flooding could face significant issues if struck.

We continue to go over the data and will provide an updated forecast by early Wednesday afternoon in case of any last-minute data changes. Stay tuned! Remain weather-aware throughout tomorrow as we brace for potentially ‘grumpy’ conditions.

Intense storms over Central Manitoba are expected to move into Northwestern Ontario on Wednesday evening. These storms could be very severe with hail up to the size of golf balls, 100 km/h wind gusts and one or two tornadoes. The storm risk will diminish after midnight as these storms slowly weaken while tracking to the east. Isolated severe storms are also possible north of Georgian Bay around the Sudbury and North Bay region.

NORTHERN ONTARIO: Thunderstorm Forecast for Wednesday, July 26, 2023

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FORECAST DISCUSSION

Intense storms over Central Manitoba are expected to move into Northwestern Ontario on Wednesday evening. These storms could be very severe with hail up to the size of golf balls, 100 km/h wind gusts and one or two tornadoes. The storm risk will diminish after midnight as these storms slowly weaken while tracking to the east. Isolated severe storms are also possible north of Georgian Bay around the Sudbury and North Bay region.

ONTARIO: Thunderstorm Forecast for Wednesday, July 26, 2023

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FORECAST DISCUSSION

Wednesday is shaping to be a potentially active day as indications point towards a strong severe risk across Southwestern Ontario during the late afternoon and evening hours. A potent environment is expected to develop, creating favourable conditions for severe weather.

Current models are suggesting the formation of a line of intense thunderstorms during the afternoon over Lower Michigan, which will track toward Southwestern Ontario by the evening. Unfortunately, this echoes last week's significant severe weather event, and areas hardest hit then are currently at the highest risk again. The exact timing of these storms will play a crucial role in the overall severe threat on our side of the border.

Presently, we are leaning towards a strong severe risk, stretching along the Lake Huron shoreline and southward into London, Sarnia, Chatham, and Windsor. As we gain more clarity on timing, the likelihood of introducing a 'significant' severe risk in this area is quite high. The severe threat could carry as far east as the GTA and Niagara region although that is questionable.

⚠️ Potential Threats

  • Destructive Wind Gusts: Expect the potential for widespread wind damage.

  • Very Large Hail: Hailstones of considerable size may cause damage to property and vehicles.

  • Flash Flooding: A major concern with localized rainfall totals of 100-150mm possible in a few hours.

  • Tornadoes: While uncertain, the environment may support a few tornadoes which is highly dependent on timing.

🕓 Timing

  • Southwestern Ontario: 6 - 10 PM

  • GTHA/Niagara: 8 PM - 12 AM

NOTE: This is a preliminary forecast and could change as we get closer to Wednesday. The forecast should only serve as a rough idea of potential threats and timing.

ONTARIO: Thunderstorm Forecast for Tuesday, July 25, 2023

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FORECAST DISCUSSION

A few pop-up thunderstorms may develop along the Lake Ontario shoreline from Kingston and through the Golden Horseshoe on Tuesday afternoon. One or two of these storms have the potential to become marginally severe with nickel-sized hail, 90 km/h wind gusts and heavy rainfall as the main threats. The strongest severe risk is in the west end of the GTA through Hamilton and Niagara region.