I live in the Seattle area. You d be talking about the mountins in Oregon and the answer is yes, you shoudl be prepared with winter tires and chains. The weather can be very unpredictable every year. You might have no problesm at all and the next year have many problems.
Your choke poiint on that trip is Siskiyou Pass on the OR /CA border Once you get about 50 miles past that then you re good to go all the way to San Diego....But watch out for fog as you get into SoCalI do agree with the previous poster who suggested being prepared for winter and carrying chains.Check with Caltrans or ODOT for Siskiyou Pass road conditions before headiing out
Try and get to Interstate 5 and follow it straight down. Being I-5 is a major freeway, it will be open. Just keep an eye and ear (radio) out for the weather.
Interstates are usually good, but there s nothing you can do about blizzards.
mountains even without snow = badunless speed racers driving you...