Ontario supercell storm: Tornadoes, large hail possible tomorrow – What you need to know

Temperatures in Southern Ontario may reach 30°C, the first of the year, as thunderstorms loom, bringing potential hazards including hail and strong winds.

Southern Ontario is in for a huge weather shift this week as a powerful Colorado low barrels in, bringing with it a taste of summer—and the threat of severe thunderstorms.

(Representational Image) Southern Ontario braces for summer-like temperatures and severe thunderstorms as a Colorado low moves in, with risks of hail, strong winds, and isolated tornadoes. (Pexel)

On Tuesday, temperatures are expected to surge into the mid- to high 20s across much of the region. If that happens, Southwestern Ontario could even see the thermometer hit 30°C, marking Canada's first 30-degree day of the year.

Early Canadian summer heat won't come without its risks

Forecast Centre The Weather Network stated, “the main hazards with any severe storm that forms will be large hail, strong winds and heavy downpours,” but there's also “a low, but non-zero risk of an isolated tornado or two with favourable, low-level shear and low cloud bases present.”

Residents are urged to “monitor the forecast on Tuesday and stay aware of potential watches and warnings in your community.”

Though, Monday will offer relatively calm weather, helping voters across Ontario as they head to the polls for the federal election. Thanks to a ridge of high pressure, temperatures will hover near 20°C with plenty of mild, pleasant conditions.

But by Tuesday morning, a Colorado low will lift into northeastern Ontario, pulling in an unusually mild and moist air mass over southern parts of the province. Temperatures are expected to run 8°C to 10°C above seasonal norms, with dew points climbing near 20°C.

Showers and thunderstorms could occur at any point during the day, especially over central Ontario and Georgian Bay. Strong storm development is also possible in northeastern Ontario. Still, forecasters say the severe weather will hit between 3 p.m. and 8 p.m.

Gusts over 100 km/h aren't out of the question. While there will be heavy downpours, the storms will move quickly, as they typically do, and so will be below 60 km per hour, helping to prevent too much flooding.

With lots of cool air aloft and the potential for strong, sustained updrafts, hailstones could grow to between 2-4 cm in diameter, roughly the size of ping pong balls.

Forecasters also caution that “there is also a non-zero, tornadic threat, especially if storms remain isolated. The cloud bases are forecast to be low, and the winds change direction as you move aloft in the atmosphere.”