On the Pacific Coast it is mild all winter, but you want to be protected from storms coming off the ocean. The rest of Western Oregon below about 500 feet of elevation will go below freezing about every third night on average, with very rare nights below 25 degrees. During the day the temperatures will be from the mid-30s into the 50s. It will also be wet much of the winter. Eastern Oregon is much colder, you will see nights below freezing and snow.

My brother and I were born and raised in sunny southern California. He married a girl whose parents moved to Oregon. He and wife followed several years later. After 3 months he called me upset... he said " I haven't seen the sun for 3 months."

The coldest I have ever been was near Salem Oregon during a cold and windy rain storm. I was wearing a heavy wool coat (lumberjack style) and blue jeans...it felt like the wind was going right through me, it chilled me to the bone.

Much depends on where specifically in Oregon. Coast has the advantage of the ocean keeping temps moderated, but as Bill says, eastern Oregon is much different.

I agree with the others. I have lived in the Eugene/Springfield area for 50+ years. it is an area that is called the Willamette Valley. It will depend on what part of the state that you are going to be working in. On the coast and in the valley we have pretty mild winters. It can freeze but not that often and more rarely anything down in the 20's or less. Portland which is on the north end of the state can get a little colder temps probably due to the Columbia River and The Gorge. We can get a lot of rain off and on here. That and you can have one week in the 50's or 60's and the next week in the 30's all mixed with rain, cloudy days, or sunny days.