The forecast for some areas affected by the storm called for temperatures above the freezing mark as well as powerful wind gusts through the weekend.
Utilities warn that's slowing repairs and even causing new outages as ice breaks off of trees and other structures onto power lines below.
Toronto — hardest hit by the storm — had 16,000 hydro customers still waiting for the lights and heat to be restored on Saturday night, seven days after the power went out.
But that's less than half the figure from a day before, while in the rest of the province about 7,000 homes and businesses are without power. In New Brunswick, thousands more were back on the hydro grid, leaving 8,400 waiting for power.
Meanwhile, the fluctuating weather resulted in see-saw progress in Quebec, where about 11,900 customers were in the same cold, dark, boat as of Saturday night.
Amid rising anger and frustration from those trying to survive without power, utility companies are pleading for patience, saying crews are working around the clock and that nothing else can be done to speed things up in what has become something akin to a war of attrition.
Toronto Hydro CEO Anthony Haines called the restoration effort "a story of ups and downs" as power is returned to one area while another is freshly knocked off-line by falling ice or wind.
"The monumental effort continues and we will not stop until every customer's power is restored," Haines said.
Toronto Mayor Rob Ford took a bolder stance, saying there is now "light at the end of the tunnel" and that he believes the repair job will be wrapped up in time for New Year's Day.
"Hopefully by worst-case scenario maybe Tuesday all the power will be restored," he told reporters.
But Haines said that while he shares the mayor's optimism that things will be over soon, the weather curveball means there's no saying just when the weeklong outages will be repaired.
"It's very uncertain as to the amount of time ahead because a job that is predictable in terms of its process is not predictable under these current conditions."
"It's just an absolutely impossible task to be able to say that, yes, on 2 o'clock on Tuesday at this pace we expect to be done," he said.
NB Power President Gaetan Thomas said it's hoped most customers will be reconnected by the end of Tuesday, but that could change depending on how a storm overnight Sunday impacts ice-laden trees in New Brunswick.
Hydro crews in Toronto — their ranks bolstered by hundreds of bucket trucks dispatched from other jurisdictions — are continuing to winnow down the number of those still in the dark.
Haines said that crews have been restoring power to about 18,000 customers each day. Some 300,000 homes and business were affected at the peak of the outages earlier this week.
— With files from Aly Thomson in Halifax
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