This week, Southern Ontario will experience a big change in weather. A powerful storm system known as a Colorado low is heading toward the region. It will bring summer-like temperatures along with a strong chance of severe thunderstorms.

Temperatures Could Reach 30°C

On Tuesday, much of Southern Ontario will feel like it's summer. Daytime highs are likely to climb into the mid or even upper 20s. In some parts of Southwestern Ontario, the mercury may reach 30°C. If that happens, it would be Canada’s first 30°C day of the year.

Summer Warmth Brings Storm Dangers

This early burst of summer warmth comes with potential risks. According to The Weather Network’s Forecast Centre, “the main hazards with any severe storm that forms will be large hail, strong winds and heavy downpours.” They also mentioned that “a low, but non-zero risk of an isolated tornado or two with favourable, low-level shear and low cloud bases” exists.

Because of this, people are advised to “monitor the forecast on Tuesday and stay aware of potential watches and warnings in your community.”

Monday Will Be Calm and Comfortable

Before the stormy weather arrives, Ontarians will get to enjoy a calm and mild Monday. A high-pressure system will keep the skies mostly clear, and temperatures will hover around 20°C. This peaceful weather will make it easier for voters to head to the polls during the federal election.

Storms Expected to Arrive Tuesday Morning

By Tuesday morning, the Colorado low will move into northeastern Ontario. This system will draw in warmer and wetter air from the south. Temperatures in Southern Ontario are forecast to be 8°C to 10°C warmer than normal for this time of year. Dew points are also expected to be high, near 20°C, which adds to the sticky and stormy conditions.

Rain showers and thunderstorms may occur throughout the day. Central Ontario and areas near Georgian Bay are likely to see some of this activity. Meanwhile, northeastern Ontario also has a chance of stronger storms developing. Meteorologists say the most dangerous weather will likely happen between 3 p.m. and 8 p.m.

Strong Winds, Large Hail, and Quick Storms

Wind gusts could exceed 100 km/h in the worst-case scenarios. While the storms will bring heavy rain, they will also move quickly—likely under 60 km/h—which could help reduce the risk of major flooding.

Because the air higher up in the sky will be cold, and the storm systems may have powerful upward motion, forecasters believe hail could grow large—up to 2 to 4 cm wide, about the size of ping pong balls.

Slight Tornado Risk Still Exists

Experts are also warning about the slight possibility of tornadoes. They said, “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.”