The large-scale weather pattern has shifted in a way that is going to give Seattle far better weather than southern California and protect us from any Japanese radiation for a while.
What configuration can provide such a boon? Large-scale troughing on the West Coast that is going to send weather disturbances to our south.
Here are two upper-level weather maps for the 500 mb level (roughly 18,000 ft).
The airflow parallels the lines and the closer they are together the stronger the winds. A strong trough will be resident along the coast and the current of strong winds...often known as the jet stream...will be heading south into LA-LA land. Thus, while substantial rainfall will be falling over CA we will remaining generally on the dry side. In fact, this is currently a flash flood watch and wind advisory for LA! And with the flow moving south into CA any radiation-bearing particles crossing the Pacific will head south toward southern CA.
The Northwest has been sufficiently wet that even if we don't get a drop for the rest of the month, we will still have normal rainfall for March.