Story updated at 5:30 p.m. Wednesday, Nov. 30
Light snow is expected late Wednesday night and Thursday morning down into Willamette Valley cities from Eugene to Portland, the National Weather Service in Portland said.
"Snow will be spotty in nature, and will be combined with rain through most locations," the agency said. "Some areas, especially those above 500 feet, may see minor accumulations while others will see no snow. While accumulation may not be heavy, be sure to travel with care as roads may still be slick in spots."
In the hills and higher elevations in the Coast Range and Cascade Foothills, in towns such as Mill City and Sweet Home, and other elevations around 1,000 feet, 2 to 5 inches of snow is possible, while elevations above 2,000 could see 5 to 8 inches.
In the higher mountain roads, another foot of snow is forecast.
Snow won't be in question at Oregon's Cascade Range pass levels, with places such as Santiam and Willamette passes, along with the Government Camp area on Mount Hood, getting anywhere from 1 to 3 feet of snow across the week.
Here’s what the week is expected to bring, according to National Weather Service meteorologist Colby Neuman.
Freezing temperatures are expected in the Willamette Valley Tuesday morning, and if there is any precipitation, it could turn to snow.
The stitch is that the rain isn’t expected to arrive until later in the day Tuesday, after temperatures have warmed enough that precipitation is expected to fall as rain instead of snow.
“It’s possible we get enough precipitation to get light snowfall in the valley, but it’s a pretty low probability at this point,” Neuman said. “It should just be cold in the morning and with some showers in the afternoon.”
Just up the road, however, in the Coast Range and Cascade Foothills, snow will be more likely Tuesday afternoon. In the Coast Range, a winter weather advisory has been issued above 2,000 feet from 1 p.m. into the evening, making driving to the Coast a challenge.
In the Cascade Foothills, towns such as Mill City, Oakridge and Detroit, are more likely to see some snow, though not too much, on Tuesday afternoon.
The heaviest rain of the week in the valley, and the heaviest snow on the Cascade Range passes, is forecast to arrive Wednesday.
A half to three-quarters of an inch of rain is forecast in Salem and Eugene as snow levels rise to about 3,500 feet. All of that rain is expected to fall as snow on Santiam Pass (Highway 20), Willamette Pass (Highway 58) and the Government Camp-Mount Hood area, likely bringing challenging travel conditions.
The snow level is expected to drop to 2,500 to 3,000 feet by Wednesday night.
“The worst time to travel would be midday Wednesday or Wednesday night,” Neuman said. “It should be dumping snow on all the Cascade passes.”
A winter storm watch for 1 to 2 feet of snow has been issued for the Cascade passes from late Tuesday night to Thursday morning.
Colder temperatures return Thursday, bringing another low-probability chance for valley snow.
“Right now, odds for one inch of snow in Salem and Eugene are around 10% and maybe up to 15% in Portland,” Neuman said.
The odds for an inch of snow in Oakridge, Mill City and Detroit are higher, at about 50%, he said.
Either way, snow is expected in the Cascade Foothills and the Coast Range Thursday and into Friday, continuing into the weekend.
Zach Urness has been an outdoors reporter in Oregon for 15 years and is host of the Explore Oregon Podcast. To support his work, subscribe to the Statesman Journal. Urness is the author of “Best Hikes with Kids: Oregon” and “Hiking Southern Oregon.” He can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on Twitter at @ZachsORoutdoors.
This article originally appeared on Salem Statesman Journal: UPDATE: Light snow probable in Willamette Valley Thursday morning