NORTHERN ONTARIO: Thunderstorm Forecast for Thursday, May 11, 2023

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Thunderstorms are possible across Northern Ontario in the morning and later in the day. The first round of storms will come just after midnight in Northwestern Ontario as a line of storms tracks into the region from Manitoba. These storms will slowly decay as they move eastward throughout Thursday's overnight and early morning hours.

A more potent storm threat is expected to materialize by the afternoon in Northeastern Ontario. Isolated severe storms will develop somewhere around Chapleau and Timmins and track to the east/southeast during the late afternoon and early evening. The strongest threat is right along the Quebec border with up to 3cm size hail and wind gusts in excess of 100km/h.

An isolated tornado can’t be ruled out in locations including Timmins, Cochrane, Englehart and Kapuskasing (as shown below).

TORNADO RISK

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ONTARIO: Thunderstorm Forecast for Sunday, May 7, 2023

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On Sunday, there continues to be the risk of isolated thunderstorms coming in two waves for parts of Southwestern and Central/Eastern Ontario. The first round will come Sunday morning in Deep Southwestern Ontario with a decaying line of thunderstorms crossing the border from Michigan.

Later in the day, we expect to see an area of rain move across Georgian Bay and across parts of Central and Eastern Ontario. Some embedded thunderstorms are possible within this rainfall during the afternoon and early evening hours.

Despite earlier indications, all storms are expected to remain non-severe on Sunday. The isolated severe risk for Southwestern Ontario is looking less probable due to the morning precipitation taking longer to move out. This slow-moving precipitation will lead to reduced daylight heating which is required for the storms to develop. As such, we have dropped the severe risk zone in our updated forecast.

NORTHERN ONTARIO: Thunderstorm Forecast for Sunday, May 7, 2023

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Rain, heavy at times is expected to affect southern portions of Northeastern Ontario to the north of Georgian Bay starting pre-dawn on Sunday. This cluster of heavy rain may have a few embedded non-severe thunderstorms around Sault Ste. Marie, Elliot Lake, Manitoulin Island, Sudbury and North Bay. The highest probability for thunderstorms will be during the late morning to early afternoon hours with the risk diminishing later in the day.

ONTARIO: Thunderstorm Forecast for Sunday, May 7, 2023

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Heavy rain is expected to work its way across Southern Ontario starting Sunday morning and continue throughout the day. Within this area of rainfall, there is the potential for a few non-severe thunderstorms to produce isolated lighting strikes, strong wind gusts and small hail.

In addition to this, there appears to be a pocket of instability that will build into Southwestern Ontario towards the later part of Sunday. This may allow for an isolated severe risk if we see storm development take advantage of this energy. However, models are suggesting that the morning rainfall may linger into the early afternoon which would make storm development unlikely.

We are going with an isolated severe risk for this area based on the potential for localized wind gusts up to 90km/h and nickel-sized hail. This may need to be downgraded in the Saturday update if storm development is looking less likely.

STORM TIMELINE

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As for timing, the primary risk will be during the afternoon and early evening hours. The severe threat will be mainly between 2-6 PM for Southwestern Ontario, but these storms will be very isolated (if they even develop) so not everyone will see storm activity.

The non-severe risk will be more widespread during the late afternoon and early evening hours across Central Ontario and the Golden Horseshoe. For Eastern Ontario, the thunderstorm threat will begin by the dinner hour and continue through much of the evening.

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!