Wild temperature swings to roll across Ontario this week
Weekend warmth gives way to a Monday cooldown. Temperatures rise again, then fall… again
Up, down, up, down. Following this week’s temperature graph across southern Ontario will look like we’re nodding in agreement that spring is one temperamental season.
An unseasonably warm and thunderous weekend will give way to a cooldown by Monday. Warmth returns by the middle of the week—only to disappear once again by the end of the week.
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Weekend warmth vanishes
Saturday night brought some southern Ontario communities low temperatures about as warm as you’d expect to see in the middle of June.
Sunday saw a renewed round of unseasonable warmth as southerly winds dragged mild air—and even some thunderstorms—north of the border.
That comfortable pattern then vanished before our eyes to start the new workweek as a sharp cold front plunges across the region.
Overnight temperatures dropped just below the freezing mark for just about everyone in southern Ontario—a far cry from Sunday’s high of 22.2°C in Port Weller, which now holds the title of Canada’s warmest temperature of 2025. Port Weller could see scattered flurries by Monday morning.
A brief warmup before the next cold front crashes the party
Back up we go by Tuesday as a warm front looks to cross over the region. The notable warmup will arrive by Wednesday as a Colorado low approaches the Great Lakes.
This system will drag plenty of mild air into southern Ontario, allowing temperatures to rise into the teens once again as far north as Parry Sound and Ottawa. Folks in far southwestern Ontario may climb into the upper teens on Wednesday afternoon.
The renewed warmth won’t be long for this world, sadly, as the Colorado low’s cold front crashes into southern Ontario by the end of the week.
Thursday night into Friday morning will get quite chilly throughout the region.
Folks in Timmins could see readings in the minus teens before the wind chill, while air temperatures in southern Ontario will dip into the minus single digits.
Stay with The Weather Network for all the latest on conditions across Ontario.