Ontario faces greatest supercell storm threat of the year (so far)
The returning humidex will help to fuel a severe thunderstorm risk across southern and eastern Ontario on Tuesday.
A potent Colorado low will bring southern Ontario a severe thunderstorm risk on Tuesday as the region gets a taste of summer-like heat.
Temperatures are expected to soar into the mid- to high 20s for parts of the region. Temperatures could even hit the 30-degree mark in southwestern Ontario. If it happens, it will be the first 30-degree reading in Canada this year.
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However, the warmth and humidity could be the catalyst for thunderstorms, with a chance of severe weather for a sizable portion of southern Ontario. The main hazards with any severe storm that forms will be large hail, strong winds and heavy downpours, but there is a low, but non-zero risk of an isolated tornado or two with favourable, low-level shear and low cloud bases present.
Monitor the forecast on Tuesday and stay aware of potential watches and warnings in your community. Conditions can change rapidly as strong storms bubble up.
Thunderstorm season ramps up with severe potential on Tuesday
On Monday, the weather will co-operate with voters heading to the polls in the federal election. A ridge in the atmosphere crests across southern Ontario, ushering in mild temperatures that approach 20°C.
But, on Tuesday, conditions will change. The heat and a first taste of humidex will work to destabilize the atmosphere and fuel thunderstorm potential.
By Tuesday morning, a Colorado low lifts into northeastern Ontario, funnelling a very mild and moist air mass across southern Ontario. Temperatures will be upwards of 8°C-10°C above seasonal with dew points sitting near 20°C by Tuesday afternoon—-highly anomalous for April.
It will feel even a little muggy for those inland, away from the chilly lake influences.
There is the risk for showers and thunderstorms throughout the day, especially in central Ontario and areas around Georgian Bay. Some stronger storms could also develop in parts of northeastern Ontario, but the greatest risk for the worst of the storms appears to be from 3 p.m. to 8 p.m.
The strongest winds will be associated with thunderstorm activity, but a more potent gust risk emerges if storms cluster into a line into the evening hours. Some of the gusts within the storms could become damaging, reaching 100+ km/h.
Heavy, localized downpours are expected but the storms will be moving at more than 60 km/h, diminishing the risk of flooding. Although there’s a lot of moisture in the atmosphere for April, storms won’t see and dump rainfall, as they’ll sweep through quickly.
Large hail between 2-4 cm in diameter is also a concern in the most organized thunderstorms. There will be lots of cool air aloft, with the potential for building strong, sustained updrafts. We could even see hail up to the size of ping pong balls.
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.
Confidence is high that southern Ontario will be in the warm sector of a Colorado low Tuesday, increasing the threat of thunderstorms.
The warmth won't last, however, as a noticeable cooldown will happen on Wednesday.
Beyond that, cooler-than-seasonal temperatures will dominate during early May, including a threat for a frost or freeze, especially outside of the urban areas. Also, another significant low-pressure system is expected by Thursday night with widespread rain, followed by a reinforcing shot of chilly weather. However, a warmer pattern is expected as we get deeper into May.
Be sure to check back for all the latest on your forecast across Ontario.