PORTLAND, Ore. (AP) — Parts of the Pacific Northwest were under an ice storm warning through Wednesday morning, threatening to add to the damage brought by a powerful winter storm that hit the region over the weekend.

Area of southwest Washington and western Oregon — including that state’s largest cities of Portland, Salem and Eugene — were expecting to see a quarter-inch to an inch (6 to 25 millimeters) of ice, while freezing rain was forecast in the Seattle area.

Schools were closed in many places, bus service curtailed and warming shelters opened while officials warned of continued treacherous road conditions and the chance of new power outages, even as crews struggled to restore electricity to thousands who have been blacked out for days.

The forecast came as much of the United States coped with bitter weather that in some places put electricity supplies at risk. Another day of record cold temperatures swept much of the Rockies, Great Plains and Midwest on Tuesday, with wind chills below minus 30 (minus 34.4 Celsius) extending into the mid-Mississippi Valley. On the East Coast, meanwhile, New York and Philadelphia ended a drought of sorts with enough snow falling for play in both cities.

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The Tennessee Valley Authority, which provides electricity in seven states, asked customers to voluntarily cut back, citing a high demand for power because of the cold. A similar plea came from the grid operator in Texas.

In Oregon, transportation officials closed 47 miles (76 kilometers) of Interstate 84, a major east-west highway that runs from Portland through the Columbia River Gorge due the threat of ice.

In the mountains, the National Weather Service warned of heavy snow in the Cascades with winds gusting to 50 mph (80 kph), mixed with freezing rain and ice that could make travel “very difficult to impossible.” A storm warning was up through Thursday afternoon.

The Pacific Northwest is more known for rain and wasn’t set to experience such Arctic temperatures but the heavily forested region is especially prone to the danger of falling trees and power lines, particularly during ice storms.

“We’re lucky to be alive,” said Justin Brooks, as he used a chainsaw Tuesday to cut up the trunks of two massive trees that narrowly missed his home in Lake Oswego, Oregon, when they fell on Saturday.

Elsewhere in Lake Oswego on Tuesday, arborist Ryan Cafferky scaled a towering 150-foot (46-meter) tree to start the laborious process of cutting it down. The city had deemed the 120-year-old tree a threat to the public because it was at risk of falling, he said.

As of Tuesday night, about 52,000 people in Oregon still remained without power, according to the website poweroutage.us. Forecasters warned residents to prepare for more power outages.

In the Portland metropolitan area, some two dozen commuter buses had suspended service or were being detoured to avoid dangerous roads since storms walloped the area a few days ago.

Weekend weather that included snow and strong winds was blamed for at least seven deaths, including that of a man killed when a tree struck his house in Lake Oswego and a woman who died when a tree crushed a recreational vehicle in Portland, trapping her and causing a fire, authorities said.

Five people in Oregon were believed to have died of hypothermia, authorities said.

Warmer air was expected to provide some relief from the frigid weather starting later Wednesday.

However, the icy morning forecast prompted Portland Public Schools, the largest district in the state, to cancel classes for a second day on Wednesday, citing concerns about possible power problems, burst pipes and unsafe school walkways and parking lots.

Beaverton School District also canceled Wednesday classes, noting that some buildings still lacked power and heat.

Courts, libraries and parks were also closed in Portland and other parts of Multnomah County.

County officials extended a weather state of emergency until noon Wednesday and decided to keep a record 12 overnight emergency weather shelters open for an additional night. The county said 1,181 people slept in the shelters Monday night, breaking the previous night’s record of 1,136.

Officials issued an urgent call for volunteers, citing the high demand for shelter services in an area where thousands of people live outside at risk of cold exposure.

“The real limitation for us right now is staffing,” said Dan Field, director of the joint county-city homelessness office. “We have to have enough people to keep the doors open of the emergency shelters.”