Rain, possible thunderstorms move in after warm start to Friday

Gary Archibald has the latest forecast for southwestern Ontario

Unseasonably warm weather will continue through Friday before a cold front brings showers and a return to more seasonal conditions across southwestern Ontario, meteorologist Gary Archibald says.

Archibald said the day began with blue skies and fair-weather clouds, but rain is expected later this afternoon and into the evening.

“It is still warm and an above-seasonal day,” he said. “Rain is the story for later this afternoon and through the evening, and this stretch of several degrees above seasonal daytime temperatures comes to an end tomorrow.”

Friday’s high is expected to reach 18 C, well above the seasonal norm of 14 C. Morning temperatures held around 9 C, with readings climbing into the mid-teens early in the afternoon in London, Ont. Warmer air has also pushed into parts of southwestern Ontario, including Sarnia and Goderich, where temperatures remain higher due to a pocket of warm air drifting east from Michigan.

Wind speeds have been variable through the afternoon, with gusts expected between 25 and 40 kilometres an hour. Archibald said winds could strengthen as the cold front moves through, triggering showers and the potential for thunderstorms later in the day.

“That cold front is the trigger for showers and thunderstorms,” he said, noting the risk increases around 4 or 5 p.m.

Archibald said the broader weather system shows a classic comma-shaped low-pressure pattern over North America, with colder air wrapped around the system and warmer air pooled over the lower Great Lakes. He said Michigan and southern Ontario have been among the warmest areas in the region over the past couple of days.

While the worst weather is expected to remain south of the border, Archibald said pockets of thunderstorms and heavier rainfall are possible locally this evening, particularly near Sarnia, Goderich and Grand Bend around the supper hour. Showers are expected to linger into the evening and overnight as the front moves west to east across southern Ontario.

Rainfall totals are forecast to range between five and 15 millimetres.

“We need the rain though,” Archibald said. “It is spring after all.”

Showers and thunderstorms remain possible between about 6 and 10 p.m., with lingering showers overnight. The chance of precipitation is estimated between 60 and 80 per cent.

Cooler conditions are expected Saturday, with a rainy morning followed by cloudier but drier conditions in the afternoon. Archibald said sunnier and warmer weather returns Sunday and Monday, with highs between 16 and 18 degrees, before temperatures trend cooler and more unsettled conditions return midweek.