Winter weather will continue to hang ominously over Southern Oregon as Thanksgiving approaches.

Winter weather will continue to hang ominously over Southern Oregon as Thanksgiving approaches.

The National Weather Service office in Medford has issued a variety of statements and advisories warning of snow and extreme cold this week.

The possibility of snow and ice prompted Butte Falls School District officials to postpone classes for two hours this morning to keep buses off icy roads.

A fast-moving, upper-level system was expected to bring another round of snow to the region overnight, the weather service warned Monday afternoon. A winter weather advisory was issued for elevations below 2,000 feet in Jackson and Josephine counties, while a more serious winter weather warning was issued for higher elevations.

The advisory noted that snow levels could dip as low as 500 feet overnight. Up to 3 inches of snow was expected below 2,000 feet, with 3 to 6 inches stacking up in the mountains. The heaviest snow — up to a foot — was predicted in the Kalmiopsis Wilderness, southwest of Grants Pass.

As the storm moves out today, it will clear the way for another winter weather hazard, a special weather statement said.

An Arctic air mass will slip into place behind the cold front. The cold air combined with clearing skies and fresh snowfall will make tonight extraordinarily cold over Southern Oregon and Northern California, the statement said. Temperatures around Medford and Ashland will dip into the teens, nearing record lows, the weather service reported.

Even the coast is expected to see freezing temperatures by Wednesday morning, with forecast lows in the upper 20s in Brookings and the Coos Bay area. East of the Cascades, temperatures likely will plunge below zero.

The weather service advises people to make sure pipes are protected and irrigation systems drained. The colder-than-typical temperatures could be frigid enough to harm sensitive plants even in protected areas.

"If commercial interests have (plant) starts in barns or greenhouses, they will have to get heat to them," National Weather Service meteorologist Jay Stockton said. "The cold could damage even those protected plants."

In Ashland, a cold-weather shelter will be open tonight at First Presbyterian Church, on the corner of Siskiyou Boulevard and Walker Avenue. The shelter is open between 8 p.m. and 8 a.m.

On Wednesday, the Presbyterian Church hosts a dinner, so the shelter will move to the United Church of Christ, 717 Siskiyou Blvd., organizers said.

Stockton said temperatures will moderate a bit, but remain fairly cold Thursday and into Friday, when the next storm moves into the region. Early precipitation on Friday could fall as snow in some areas, he said.