Hope this helps:
I would advise you to come up 101 from the bay area, little chance of any snow this way. (Avoiding Grants pass, I-5).
This is "normal" weather in Washington in March.
It can be sunny and 60 degrees, for a week straight, it can rain sideways and be 50 degrees for a week straight, or it can rain one day, be nice the next for a week straight.
Just depends what week(s) you are here.
There is a chance of frosty mornings, but not
"freezing, gotta worry" type cold.
The closer you are to the ocean, the more moderate the temps as the ocean keeps it from getting too cold here.
It can freeze in Seattle but be 40 degrees at the ocean in the morning.
The east side the state can be really cold that time of year, Oregon and Wash both.
2001 Monaco Windsor 40 PBD