Southern Ontario braces for sleepless night as intense thunderstorms roll in, heatwave follows

Stormy skies tonight, sunshine tomorrow
Families across Southern Ontario are keeping one eye on the skies and the other on the radar as a fast-moving line of severe thunderstorms heads eastward overnight. With damaging wind gusts and intense rainfall expected, Thursday night, May 15, is shaping up to be one of disruption before Friday, May 16 flips the weather script.

CTV London meteorologist Julie Atchison issued a warning Thursday evening, noting that while the system will arrive fast, it will also be gone by morning. “The main threats are damaging wind gusts and torrential downpours,” Atchison explained. “This line of storms is set to push through southern Ontario after midnight into London … the line will continue to move eastward.”


Also read: Midnight tornado watch stuns Southeast Michigan as storms rip through state

Communities along the storm path could see anywhere from 10 to 15 millimetres of rainfall, though Atchison cautioned the totals could rise depending on how the cells develop. Thunderstorms are expected to begin late in the evening and will taper off before dawn, allowing Friday to usher in a dramatic change.

Thunderstorms overnight, then a blast of heat
Once the storm system clears, southern Ontario will be waking up to a very different scene. Atchison says that by morning, “the system is history.” In its place? Clear skies, sunshine, and a dose of heat and humidity that will make it feel like summer has arrived early.

Friday’s forecast calls for a high of 27 degrees Celsius with a humidex of 31. Winds from the southwest will sweep across the region by midday, adding to the warm and sunny conditions. It will be the kind of day that makes you forget about the previous night’s chaos, unless, of course, the storms leave damage behind.

The severe thunderstorms, damaging winds, and risk of heavy rainfall are all part of a shifting early spring pattern that has left southern Ontario toggling between mild spring days and more dramatic weather events. The combination of storm threats and sudden heat makes this a key weekend for residents to stay alert and weather-aware.

Also read: Ottawa is heating up fast, find out how hot it’s getting this week

Cooling down for the long weekend
After Friday’s summer-like weather, the region will ease back into more seasonable conditions for the long weekend. Saturday will be mostly cloudy with a 40 per cent chance of showers and a high of 20 degrees. Sunday is expected to remain cloudy with a cooler high of 16.

By Monday, the sun returns just in time for holiday plans, offering a high of 17 and clear skies. Tuesday brings a mix of sun and cloud with a high near 18, marking a return to the kind of mid-May weather that’s a little less dramatic, and a lot more predictable.

Southern Ontario’s forecast at a glance:
Thursday Night: Increasing cloudiness, 30 per cent chance of early showers, with heavier showers or thunderstorms beginning late evening and ending overnight. Low of 16 degrees.

Friday: Clear skies with sunshine and heat, high of 27 degrees, humidex of 31.

Saturday: Cloudy with a 40 percent chance of showers, high of 20.

Sunday: Overcast skies, high of 16.

Monday: Sunny and pleasant, high of 17.

Tuesday: A mix of sun and cloud, high of 18.