‘Strong, damaging bursts of winds’: Severe thunderstorms could hit Toronto on Tuesday. Here’s what you need to know

Cyclists make their way through Toronto during a thunderstorm on Wednesday, June 13, 2018. THE CANADIAN PRESS/ Tijana Martin

Meteorologists say some of the most severe supercell thunderstorms of this year could rip through parts of southern and eastern Ontario on Tuesday afternoon.

Environment Canada has issued preliminary guidance about the potential for “strong, damaging bursts of winds” exceeding 110 km/h, large hail of up to four centimetres in diameter, and tornadoes barging through areas in the province, including the Greater Toronto Area, Geoff Coulson a warning preparedness meteorologist with Environment Canada told CTV News on Monday.

Toronto could potentially see the weather take a dramatic turn late afternoon on Tuesday, Coulson says, while areas east of the Georgian Bay could see as many as two rounds of thunderstorms that morning.

“Those aren’t expected to be severe, but they will still produce lightning and some locally heavy rain,” he says.

“As the afternoon wears on, a cold front will move through southern and eastern Ontario, kicking off potentially long lines of thunderstorms that could affect areas from the Ottawa Valley through the Greater Toronto Area down in towards London and Windsor and specifically to Toronto.”

When are the thunderstorms expected?

Environment Canada is forecasting a 70 per cent risk of thunderstorms in Toronto on Tuesday, and Coulson says they could start at around 5 p.m. and last until 9 p.m. After then, Coulson says the “worst of the storm activity” is expected to move down into New York.

However, that timing may change as the weather agency gets more information when these storms start to develop.

It is expected to be a one-day storm, but the factors could be subject to change.

The weather agency has not issued any weather alerts currently.

What causes thunderstorms?

“We have a lot of ingredients that are going to be coming together tomorrow,” Coulson explains. “One of the most important is a lot of heat and humidity near the surface.”

Tuesday will bring one of spring’s warmest days with a forecast of 24 C that feels like 29 C with the humidex.

Warm, humid air is one of the key ingredients for thunderstorm development, he says. If the air starts to rise, it’s going to keep rising, Coulson says, and these “rising columns of air” feed the development of thunderstorms, creating a very unstable atmosphere.

Another important ingredient is a “lifting” mechanism that makes the air rise, Coulson says.

“That’s going to be this cold front, which can be thought of as a wedge of cooler air driving into the warm moist air, making it rise significantly,” he says.

Once the cold front moves through Toronto, temperatures are expected to dip and stay at around 13 C for the rest of the week, with a sunny Wednesday and possible showers on Thursday and Friday, according to Environment Canada.

How to prepare for major thunderstorms

“It’s an opportunity for people to look around their properties and to secure loose objects,” advises Coulson.

“Some of these storms do produce very strong wind gusts or tornadoes, these types of winds can pick up loose objects cause them to be projectiles, make them dangerous to people outside, or cause even more damage when they strike buildings and trees and things of that nature.”

People who own lawn furniture and other loose objects on their property may want to secure those things or move them indoors to keep them from flying around.

Coulson says severe thunderstorm watches are issued a few hours before the storm rolls in, so he advises keeping an eye out for any alerts to know when your area could be at risk.

“As we get closer to the midafternoon time frame, some of those watches could, in fact, become warnings to say that the storms are forming or may have already formed and could be producing damage in that area,” Coulson says.

It is advisable to keep a weather app handy to access and monitor the latest weather information closely, he says.