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Damaging Winds Possible as Severe Thunderstorms Target Southern Ontario

We are watching the risk for our first round of severe thunderstorms across Southern Ontario this season as a cold front is expected to swing across the region Friday morning.

Thunderstorm Forecast, for Southern Ontario. Issued March 20th, 2020.
Thunderstorm Forecast, for Southern Ontario. Issued March 20th, 2020.

Areas in green and marked with a '2' can expect a low risk for severe thunderstorms. This includes a large portion of Southern Ontario.

We are expecting scattered showers from the early morning warm front to linger across Eastern Ontario in the morning hours between 6 and 10am while the cold front will begin to push through the region. The warm front will bring widespread winds of 50-70km/h with gusts between 80-100km/h over the Niagara and Prince Edward County regions.

As this cold front pushes across Southern Ontario, starting near Lake Huron between 7am and 9am, scattered thunderstorms may develop along the front. These thunderstorms will be fast-moving, possibly over 100km/h. Isolated severe wind gusts at the surface level may surpass 90km/h alongside some small hail in the strongest cells. Currently, we expect the thunderstorms to develop in a line from Sarnia and Lake Huron through to Brussels/Wingham and Durham/Markdale.

This line will move south with additional thunderstorms developing along the front. We expect intensity will begin to strengthen into Middlesex and Perth County through to Barrie. There are some indications that some stronger storms are possible towards Haliburton and Orillia, although these may remain sub-severe.


It is questionable whether or not these thunderstorms will develop through to Windsor and Essex County.

As the line moves southeast towards Woodstock, Niagara, Toronto, and Kingston, isolated severe wind gusts in a few of the stronger cells will be possible. Brief severe thunderstorm-related alerts from Environment Canada are possible. Into Eastern Ontario between Ottawa and Montreal/New York Border, isolated clusters of thunderstorms, some severe will be possible into the early afternoon.

The main threat with all thunderstorms will be wind gusts near 90km/h, although some storms may produce small hail. Rainfall totals from the event will likely range between 5 and 15mm across most of the region with some areas, more frequent to storms, pushing totals up and over 30mm. This is most likely towards Brantford and Niagara.

Although much of the region is highlighted under this low threat, the severe thunderstorms will be isolated with only a few places seeing the severe criteria.

Areas in blue and marked with a '1' can expect mainly non-severe thunderstorms. It is questioned whether or not the cold front will start producing storms further north than the severe region, therefore, the minor risk is shown above the green 'low' region.


Following these thunderstorms and spring temperatures (in the early morning), a rapid drop in the temperature into the low negative single digits, possible reaching towards the negative double digits and brief lake-effect off of Lake Huron will be possible. Areas to the east of Lake Huron could pick up a trace to 2cm, mainly towards the north like Owen Sound.

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