A balmy Halloween for Ontario, Quebec as October temperature records broken

A warm puffer jacket has ruined many a Halloween costume in Canada, as chilly late-fall temperatures often get in the way of the perfectly curated look. 

But record-breaking temperatures are making many places in Ontario and Quebec feel more like summer. Toronto, Montreal, Ottawa, London and a swath of other cities in the region are forecast to hit record highs for Oct. 31.

• CBC Climate Dashboard: See how the weather in your city compares to historical trends

The hot temperatures stem from a large area of high pressure over the southeastern U.S., which is bringing much warmer than normal air all the way up to southern Ontario, according to Environment and Climate Change Canada warning preparedness meteorologist Geoff Coulson.

"Many people would be forgiven going outside on a day like today and thinking it was more like late August or early September as opposed to late October," Coulson said.

That pattern, he says, will end later in the day on Oct. 31. A cold front is expected to sweep through, causing some rain or even thunderstorms in Ontario. 

"Those showers and thunderstorms will likely occur around the time the kids are out trick-or-treating," Coulson warned.

WATCH | Trick-or-treaters see Ottawa's warmest Halloween on record:

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Ottawa’s Halloween forecast sits at 23 C — 1.5 degrees above the record set in 1989. The CBC’s Natalia Goodwin spoke to kids and parents about what that means for this year’s trick-or-treating.

Warmest Halloween on record

Toronto is forecast to hit a high of 24 C, the warmest Oct. 31 on record for the city and 13 degrees above average. The previous day, Toronto hit a record-breaking 22 C. 

Montreal is seeing similar conditions, forecast to hit 22 C on Oct. 31 — 12 degrees above average.

The unusual temperatures have come for a large part of the U.S as well, with higher-than-normal temperatures from Texas to Michigan and the northeast. New York City is expected to hit a balmy 25.5 C on Oct. 31, according to the U.S. National Weather Service, some 10 degrees above normal.

Coulson said temperatures will start to get more seasonal by Friday and into the weekend. 

2024 could be warmest year

The temperatures come after a series of record-setting hot months, caused by climate change and the El Niño weather pattern. 

This summer was the hottest on record, according to the Copernicus Climate Change Service, a research institution of the European Union. August 2024 was 1.51 C above pre-industrial levels, while average global temperatures were 1.64 C above pre-industrial levels for the 12 months from September 2023 to August 2024, raising alarm bells ahead of the UN climate change conference in Azerbaijan next month.

Copernicus says it is "almost certain" that 2024 will be the warmest year on record.

Environment and Climate Change Canada, meanwhile, studied 37 of the worst heatwaves across the country from June to September this year. All were made more likely by human-caused climate change.

What's in store for winter

Scientists are now waiting for the La Niña weather pattern, which usually follows an El Niño and brings cooler temperatures to the U.S. and Canada. Coulson said there are signs that La Niña is developing, although it may be a weak one.

"When it does develop, the La Niña phenomenon itself tends to impact more the winter months in southern Ontario, and the impacts tend to be more related to precipitation than temperature."

He added that the long range weather model suggests that overall, the winter is expected to a little warmer than normal in southern Ontario.