Flash freeze possible in Ottawa after 10-20 mm of rain

A messy storm bringing warmer air before cool weather to the nation’s capital is causing well-above-seasonal temperatures for this time of year.

According to Environment Canada, the city can expect rainfall amounts of 10 to 20 millimetres on Friday, followed by rapidly plummeting temperatures, causing a possible flash freeze.

Wind gusts will pick up to 60 to 80 kilometres per hour.

“Rain will overspread the area tonight before changing over to flurries from west to east through the day on Friday as temperatures rapidly fall below the freezing mark. This will be the result of a strong cold front passing through the area,” it said.

Temperatures are hovering around 4 C and sunny on Thursday.

Friday the high should be around 7 C, the weather agency said, well above the -4 C maximum normal for December. The warmest it’s ever been on Dec. 19 was in 1957 when temperatures climbed to 9.4 C at the Ottawa International Airport.

Rapidly plummeting temperatures are expected over the weekend, with overnight temperatures feeling closer to -11 on Friday and an anticipated -14 C on Sunday night.

Potholes expected to develop

The freeze-thaw cycle not only provides opportunities for icy conditions but is a prime condition for potholes, CityNews chief meteorologist Natasha Ramsahai said. 

She said milder temperatures soften up the road base and create small puddles of water. The water freezes and pushes up the concrete.

“It adds extra stress, tires go over it, and once you get into drier weather, it leaves this hole underneath the concrete,” said Ramsahai. “Then you get the weight of the tires coming through, causing the hole to collapse, and you are left with a good old-fashioned pothole.”

The Rideau Canal Skateway remains closed, especially as temperatures rise, the National Capital Commission reminded people. However, crews were able to start flooding the canal earlier this week.