Severe Thunderstorm Threat Grows Across Southern Ontario with Tornado Risk Tuesday

Southern Ontario is bracing for a volatile day of weather as summer-like heat sets the stage for potentially severe thunderstorms Tuesday afternoon and evening. With all hazards possible—including damaging winds, large hail, and even a risk of tornadoes—residents are urged to stay weather-aware throughout the day.

Temperatures are expected to soar into the mid- to high-20s across much of the region, with southwestern Ontario possibly touching the 30°C mark. The combination of heat and humidity will destabilize the atmosphere, creating ideal conditions for strong thunderstorms to develop. Dew points climbing near 20°C by the afternoon—an unusually high level for April—will make it feel muggy, especially inland away from the cooler lake influences.

The main window for severe weather will open between 3 p.m. and 8 p.m., when storms are expected to become more organized ahead of an approaching cold front. Some areas may see multiple rounds of thunderstorms, particularly across the Greater Toronto Area and eastern Ontario, while southwestern Ontario faces a more isolated risk.

Severe thunderstorms that form could bring damaging wind gusts potentially exceeding 100 km/h, heavy downpours, and hailstones between 2-4 cm in diameter, with the strongest updrafts possibly producing hail the size of ping pong balls. While the storms will be capable of intense rainfall, their fast movement—at speeds over 60 km/h—should minimize widespread flooding risks.

One of the more concerning elements for today is the potential for tornadoes. Low cloud bases combined with shifting winds aloft—a condition known as wind shear—could allow storms to develop rotation. Supercell thunderstorms, the type most capable of producing tornadoes, are possible by late afternoon.

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Although the severe weather risk will dominate Tuesday, the warm and stormy conditions will not last. A noticeable cooldown is expected to arrive on Wednesday, ushering in temperatures that will dip below seasonal norms for the early part of May. Frost or freeze conditions could occur later this week, particularly in rural and suburban areas outside the urban heat zones.

Adding to the unsettled pattern, another significant low-pressure system is forecast to move in by Thursday night, bringing widespread rainfall and reinforcing the cooler weather. However, forecasters anticipate a return to warmer conditions as May progresses.

With the atmosphere primed for rapid changes, residents across southern and eastern Ontario should closely monitor forecasts, keep an eye on the sky, and be prepared for watches and warnings throughout the day.