Severe Thunderstorm Risk and Heavy Rain to Kick Off the Weekend Across Southern Ontario

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It has certainly been a rollercoaster month for the weather in Southern Ontario! Last week, we experienced near-record-breaking temperatures, giving us a taste of summer. This week, reality hit with chillier temperatures and accumulating snow in some areas. As we approach the weekend, warmer air will return with daytime highs in the upper teens and low 20s on Friday. However, this warmer air brings a risk of thunderstorms and heavy rainfall over the weekend.

The warmth comes from tropical air being pumped into our region from the Gulf of Mexico, but it also carries the threat of rainfall over the next 36 hours across Southern Ontario. Pop-up showers have already begun developing over Michigan and Southwestern Ontario, with rain expected to expand eastward throughout the afternoon and evening, reaching the Golden Horseshoe by dinner time and Eastern Ontario by late evening.

We're also monitoring the risk of a few embedded thunderstorms developing later this afternoon and early evening in advance of this system. The environment is favourable for these storms to become marginally severe, primarily around the Hamilton and Niagara region, extending across the GTA and into Kingston later in the day. Our main concern is large hail up to quarter to loonie size and wind gusts near 90 km/h.

Models consistently show the Niagara region at the highest risk of these storms, so we've given them a slight risk of severe storms. However, this risk is questionable, and we were on the fence between isolated or slight risk zones. We don't expect much of a tornado risk with these storms, but as always, it can't be completely ruled out with any severe thunderstorm.

There's also a questionable risk of a severe thunderstorm on Saturday in parts of Eastern Ontario. At this point, it looks like an isolated risk, and storm development may not even happen. We will be watching and will issue a forecast tonight or early Saturday based on the latest data should severe storms still look possible.

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Aside from the severe risk, this weekend is shaping up to be quite wet across Southern Ontario. Rainfall totals across a wide swath of our region, including London, K/W, Toronto, Barrie, and Muskoka, will range from 15 to 30mm by Sunday morning. This could worsen the flooding experienced in some parts of the province, as is typical during this time of year.

Deep Southwestern Ontario and Eastern Ontario can expect slightly less, with 10 to 20mm of rain anticipated. Scattered showers may linger into Sunday, adding a few additional millimeters of rain in some areas. Remember that with the risk of thunderstorms, localized regions may exceed the forecasted rain and approach 30-40mm.

Another Week, Another Season; Accumulating Snow Returns to Parts of Southern Ontario for Monday and Tuesday

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Reality is setting in across Southern Ontario, reminding us that it isn't done with us just yet, despite the unseasonably warm weather we've enjoyed last week and into the weekend. We're in for a rollercoaster ride as temperatures drop from the 20s and even lower 30s a few days ago to daytime highs struggling to reach double digits in the coming days. The colder air will also bring back a sight we thought was behind us - snowflakes falling from the sky!

Indeed, we are looking at the risk of flurries and wet snow over the next couple of days across much of Southern Ontario. We've already seen some flakes in parts of Deep Southwestern Ontario early this afternoon. The potential for snow will encompass much of Southern Ontario by later tonight and into the overnight hours as temperatures drop to near the freezing mark. We aren't expecting significant accumulation, and with the ground still somewhat warm from last week's heat, much of what falls will likely melt on contact.

However, we do see the chance of minor accumulation east of Lake Huron and Georgian Bay, where lake effect snow could boost snow totals in those regions. Some higher elevations east of Lake Huron through parts of Huron, Bruce, Grey, and Perth counties could see up to 4-8cm of accumulation! Surrounding regions, including Central Ontario, may see a light dusting of snow, especially during the overnight hours when temperatures will be cold enough to allow for accumulation.

Scattered flurries will continue throughout the day on Tuesday, with the heaviest snow found east of Lake Huron and Georgian Bay. It appears Eastern Ontario will mostly escape the snow, as this will be mainly a lake-driven event. However, they could see a few flakes later in the day on Tuesday and Wednesday mornings as the moisture associated with this system moves out of the region.

Keep in mind, actual accumulation may vary due to temperatures being very close to the freezing mark. As such, totals may be lower than forecasted, given the potential for some snow to melt on contact with the ground. It will come down to how cold the temperature can get during the overnight hours, which will dictate how much snow will stick to the ground.

Be sure to take your time on the roads if you need to travel, as many have likely already switched from winter to summer tires. While this won't be a high-impact event, it could cause some delays since drivers haven't had to deal with wintry weather in a while. Stay safe!

Possible Severe Thunderstorms on Sunday to End Off a Stretch of Summer-Like Weather Across Southern Ontario This Week

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As the saying goes, 'All good things must come to an end,' and that will become apparent on Sunday as we cap off what has been a stellar week when it comes to the weather. We saw temperatures well into the 20s for multiple days this weekend, which is rare in April. A cold front is expected to slide across the region during the afternoon and evening on Sunday, ushering in much colder air. In addition to providing a sharp drop in temperatures, the front will also spark off another common summer weather phenomenon - thunderstorms!

A line of rain is expected to develop ahead of the front and track across Southwestern Ontario and into the Golden Horseshoe starting just after the lunch hour and continuing throughout the evening. This line will likely have embedded thunderstorms which should remain non-severe for the most part. However, the environment is strong enough to allow an isolated storm to briefly become severe, with the main threat being 90km/h wind gusts and up to pea-sized hail.

The risk zone for the isolated storm includes all of Deep Southwestern Ontario and into the Hamilton/Niagara region. Remember, this is only an isolated risk, and any strong storms will be very localized. Not everyone will see a severe storm tomorrow. Outside of the severe threat, non-severe thunderstorms could deliver heavy rainfall and frequent lightning strikes across much of Southern Ontario. Eastern Ontario could see a few lightning strikes later overnight and pre-dawn Monday, but we didn't include them in the map as this is for Sunday only.

We will continue to monitor the latest data and may update this forecast by early Sunday afternoon if needed. Stay safe!

First "Elevated" Severe Thunderstorm Risk of 2023 Incoming to Southern Ontario (Wed, Apr 5, 2023)

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A line of severe thunderstorms is possible across Southwestern Ontario on Wednesday and the risk will extend into isolated parts of Central, Niagara and the GTHA. The morning will bring heavy rain, hail and thunderstorms but the afternoon and evening will bring the strongest risk for damaging wind gusts (120km/h+), large hail (2-4cm), isolated flooding (50mm+) and frequent lightning. While the strongest risk remains stateside, the possibility of intense storms crossing continues to increase with each model run.

We’ve also identified an isolated tornado risk for much of Southwestern Ontario, stretching into parts of the GTHA and Niagara. There is a slightly more enhanced risk in deep southwestern Ontario closer to the US border and Lake Erie as well. However, we’ve seen models suggesting the risk could be a bit more widespread and further to the north. We may upgrade this risk but for now, we feel an isolated tornado region covers the chance of isolated tornado spin-ups tomorrow.

Be sure to stay informed and monitor weather updates as this potent storm system approaches. The impact of freezing rain, heavy rainfall, and possible severe thunderstorms, combined with significant ice accretion and potential power outages, could cause some disruptions to daily routines and travel plans.