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.