http://ottawacitizen.com/news/local-news/flash-freeze-warning-ends-ottawas-brief-taste-of-spring
The brief, two-day January thaw came to a bone-chilling end Friday afternoon.
Ottawa residents who woke up to a balmy 11 C Friday morning found themselves driving home that afternoon through a mix of snow, freezing rain and ice pellets, with the temperature plunging to a low of -15 C.
Environment Canada had the area under a “flash freeze” warning Friday and by Saturday night, the mercury was predicted to be down to a polar-like -26 C.
“It’s a pretty dramatic swing in temperature,” acknowledged Environment Canada meteorologist Geoff Coulson.
After a couple of days of warm, moist air from the Gulf of Mexico, a mass of frigid Arctic air swept in “and the door slammed shut,” he said.
“We’re seeing another Arctic air mass and it’s another dominant one. We’ve got cold warnings out in the Prairies, cold warnings in northern Ontario. It’s not necessarily the depth of cold that we dealt with last week, but it’s still certainly well below normal.”
Ottawa should escape the heavier snowfall expected to the south, however. Kingston and Cornwall could see up to 20 cm of snow, whereas Coulson expects Ottawa’s accumulation will be between five and 10 cm by the time the snow ends around mid-day Saturday.
About 300 to 400 City of Ottawa plows and salters were set to hit the street Friday, their task complicated somewhat by the deep pools and puddles in many areas. City workers — and many private citizens — worked Friday to clear ice-clogged catch basins to drain the flooding.
“Today is a bit of a challenge because we have a lot of standing water on the roadways,” said Bryden Denyes, the city’s area manager for core roads. “We’re doing our best to ensure we get most of that off the road … The quick temperature drop does pose a challenge, but staff are monitoring that.”
Road salt loses its effectiveness at temperatures below -18 C. In that case, the city pre-soaks the salt which kickstarts the melting process, and adds grit to the mix that can help with traction.
Driving could be pretty rough on some smaller side streets when ridges of slush are frozen solid by the deep freeze. The city will use road graders if necessary to scrape the ridges away, Denyes said.
The thaw also has created dangerous and unstable ice conditions on waterways, warns the Rideau Valley Conservation Authority.
In some areas, the thaw has led to an ice break up, which raises the potential of downstream ice jams and flooding. In other areas, rain and meltwater has pooled on the surface, and though that will soon refreeze when the temperature plummets, it will take several days of cold weather before the ice is safe enough to walk on again, the conservation authority warns.
The rapid temperature fluctuation isn’t just hard on people and drivers. Buildings and roads take a beating, too.
Small foundation cracks can quickly widen with repeated freeze-thaw cycles, which is why it’s important to do regular maintenance and patch them, Coulson said.
“In terms of pipes freezing, we are getting into some pretty cold temperatures by Saturday night and Sunday morning. It’s certainly something to be aware of. The number of freeze-thaw cycles we’ve gone through in the last few days, we’ve got a lot of water main breaks — a lot more than we saw last year, which was a notably milder winter,” he said.
The temperature will stay low into next week, with daytime highs of around -10 C and overnight lows dipping to -16 C.
bcrawford@postmedia.com
Twitter.com/getBAC
