Olympia Wa. to Phoenix Az. In Dec.

I recommend bypassing 101 that time of year. Too much wind, rain and morning fog (usually).

I-5 is your best bet. The highest point is the pass at the Oregon-California's border (Siskiyou Pass). In my 40+ years of travelling that area as a salesman I was only delayed ONE time for about three hours when I was heading home (north).

Just watch the weather reports and plan accordingly. If you do chain up you can put chains on the outside tires. Or both. Your choice.

Safe travels!

Oregon Chain Law

Oregon's chain law applies to all highways throughout the state. When you drive in winter conditions, you may see signs telling you to carry chains or traction tires and when you are required to use them. In some areas, lighted message signs also will advise you about chaining up. Traction tires may be used in place of chains on vehicles rated at 10,000 pounds gross vehicle weight or less and that are not towing or being towed.

Studded tires are legal in Oregon from November 1 through March 31. Because of the damage caused by studded tires, the Department of Transportation encourages motorists to use studded tires only when necessary. Delaying putting on studded tires or using other traction tires is helpful to the condition of the highways.

For placement of chains or traction tires go to Minimum Chain Requirements. For information on traction tires go to Traction Tires.

101 is definitely doable. But, be aware where you might not have snow, and even that is no guarantee, you will encounter lots of rain and wind. That can make for some really ugly driving.

Washington, Oregon and many other states have the same or very similar chain placement.
WA chain placement
There is no way on trip to go without going over passes that require you to carry or install chains. WA & OR require chains to be installed on vehicles over 10,000 pounds when traction tires are required on autos.
Going south on I-5 is about the best choice. Yes, watching weather is necessary.
Are you going single or pulling trailer? If pulling trailer you need a set of chains for the farthest rear braking axle as well.

I-5 typically can be rainy and foggy in the winter with the exception of Siskiyou Summit south of Medford, OR. Time your trip. Once in awhile there is a cold front in the PNW and they can get some snow. It is usually cleared off I-5 quickly.
If you have 4wd you will almost never need chains. It is still a good idea to carry them in winter. If you need chains on a 4WD vehicle the Highway Patrol will close the roads in most states.
You can get by with a pair of chains on the outside rear wheels. Towing a trailer in snow is almost always a bad idea.

donn0128 wrote:
Carry chains for sure. Stop at any Les Schwab tire store and buy a set. They have a no use free return policy just to be safe. BTW, Oregon does have a law, chains or traction devices required for winter travel. They also say to carry in mountains. You may only need them from just north of Redding to Myrtle Creek, possibly as far north as Eugene.

Thanks for the info. considering the 101 down the coast.

Carry chains for sure. Stop at any Les Schwab tire store and buy a set. They have a no use free return policy just to be safe. BTW, Oregon does have a law, chains or traction devices required for winter travel. They also say to carry in mountains. You may only need them from just north of Redding to Myrtle Creek, possibly as far north as Eugene.