Portland weather forecast: Storm will start off as snow early Thursday across … – The Oregonian

1:55 p.m. UPDATE: Weather forecast gets worse: Expect ‘significant’ snow for Portland, blizzard-like conditions in Columbia River Gorge

One more day of high winds and below-freezing temperatures Wednesday will transition into what’s shaping up to be a snowy, icy mess early Thursday morning across northwest Oregon and southwest Washington.

Forecasters say precipitation from a low pressure system off the Oregon Coast will likely begin as snow for the north Willamette Valley on Thursday morning, with 1 to 4 inches of snow accumulating across the Portland metropolitan area.

Heavier snow of 2 to 6 inches is possible for parts of Washington and Yamhill counties, west of Hillsboro and McMinnville.

As is the case when cold air funnels into the region through the Columbia River Gorge and collides with a warm, moist Pacific storm, timing is everything.

View full size Hour by hour forecast temperatures and precipitation from 8 a.m. Wednesday through 8 a.m. Friday for Portland.

The latest forecast models show areas north of Salem starting to see bands of light snow move through as early as 4 a.m. Thursday, said Clinton Rockey, a forecaster for the National Weather Service in Portland.

“The first bands of moisture from this system will be light because it’s coming into really dry air,” Rockey said. “But from about 6 to 7 to 8 a.m. we could see a couple of inches in the city. It’s going to be a lovely commute.”

Rockey expects a gradual warm-up to begin about mid-morning Thursday, with snow transitioning to a mix of snow, freezing rain and sleet before turning to all rain except for locations close to the western mouth of the Columbia River Gorge: Troutdale and to the east.

The gorge, north Oregon and south Washington Cascades are under a winter storm watch, with 4 to 8 inches of snow forecast for areas close to the Columbia River, and more in the upper Hood River Valley. The Cascades could see 1 to 2 feet of snow, with the highest amounts in the south Washington Cascades.

To make matters worse, the Cascades could also see freezing rain late Thursday, with as much as a quarter inch of ice possible.

With cold air in place and high winds again Thursday, wind chills will drop below zero degrees making travel through the Columbia River Gorge and Cascade mountain passes extremely hazardous. The upper Hood River Valley will get cold and snowy and may not even see a transition as the cold air remains locked in place, forecasters say, well into the weekend.

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Rockey said precipitation will taper off from the north to the south on Friday, but there remains a chance for yet another challenging commute early Friday morning as a reinforcing shot of cold air and more precipitation rotates in over the region.

The weekend looks dry, but don’t look for an end to brisk east winds and cold temperatures pouring out of the western end of the Columbia River Gorge into the Portland metropolitan area.

Portland forecast

Wednesday: Mostly sunny, with a high near 42. Breezy, with an east wind around 23 mph, with gusts as high as 36 mph.

Wednesday night: Snow, possibly mixed with freezing rain, mainly after 4 a.m. Low around 29. East wind around 17 mph, with gusts as high as 24 mph. Chance of precipitation is 80 percent. Little or no ice accumulation expected. New snow accumulation of less than one inch possible.

Thursday: Snow, possibly mixed with freezing rain before 10am, then rain. High near 36. Southeast wind 13 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 100 percent. New ice accumulation of less than one-tenth of an inch possible. New snow accumulation of 1 to 2 inches possible.

Thursday night: Rain. Low around 35. East wind 7 to 9 mph. Chance of precipitation is 90 percent. New precipitation amounts between one-half and three-quarters of an inch possible.

Friday: Rain likely, mainly before 10 a.m. Mostly cloudy, with a high near 47. East wind 5 to 9 mph becoming south in the morning. Chance of precipitation is 60 percent. New precipitation amounts of less than one-tenth of an inch possible.

Friday night: A 20 percent chance of rain. Mostly cloudy, with a low around 31.

Saturday: A 20 percent chance of rain. Mostly sunny, with a high near 40.

Sunday: Mostly sunny, with a high near 40.

— Stuart Tomlinson