Snow in Portland

Snow sticks to the ground Monday, Dec. 5, 2016, at Mount Calvary Cemetery in the Sylvan-Highlands neighborhood of Portland.

(Stephanie Yao Long/Staff)

Though Tuesday's sunny skies were a departure from Monday's snow flurries, this week's winter weather isn't over quite yet.

Freezing fog and frost could make roads dangerous Tuesday night and Wednesday morning, National Weather Service meteorologist Colby Neuman said. Fog could limit visibility and frost could act as black ice, making roads slick, he said.

But the bigger problems are expected Wednesday night - when "an unusually strong winter storm" is set to hit the region, the weather service said. Northwest Oregon and southwest Washington are under a winter storm watch for freezing fog, snow and freezing rain, the weather service said. The watch is in place until Thursday afternoon.

The watch covers the Portland area, the Interstate 5 corridor, the lower Columbia region of southwest Washington and northwest Oregon and the Cascade foothills in north Oregon and south Washington.

The storm brings an 80 percent chance of snow to the metro area between 4 a.m. and 8 a.m. Thursday, Neuman said. That snow is expected to turn into sleet and then freezing rain Thursday afternoon and evening.

"It's a pretty good bet that this will be a bigger deal than what we saw on Monday," Neuman said.

Snow accumulations could range from 1 to 4 inches in valley areas and the coastal mountains, and 2 to 5 in the Cascade foothills. Up to a quarter inch of ice could accumulate.

The snow and ice will make roads slick and potentially dangerous, the weather service said.

It's still too early to predict many of the details of the storm, such as when snow will turn to sleet and freezing rain, Neuman said. In the meantime, people should prepare for icy conditions on their morning and evening commutes, he said.

-- Samantha Matsumoto