snow is an issue. I think it snowed on the valley floor in March, but I can't find any data, but I do know that the first three months of 2017 were very poor weather condition months. But another issue is congestion and don't plan on a hour by hour drive schedule from Washington /oregon Border to Eugene Oregon. If you hit portland between 11:00 am and 1:30 pm, then there should be no problem. Portland traffic is only dependable between those two and half hours, after that or before that it is a mess. And once you are south of Salem, there is way too much traffic for that two lane freeway. And if it is raining, than that is compounded. so if you don't like snow, then there is the coast hwy for an extra day of travel, though if it is storming in the passess, then it is pounding rain on the coast.