Today is a good example. Here are precipitation measurements over the 24-h ending 9 PM Sunday evening. On the southern and southeastern sides of the Olympics they got hit by 2 to 3 inches of rain, while virtually nothing fell on much Lopez and San Juan Island. Not much more on northern Whidbey. In fact, the rain shadow extended as far a Bellingham! There is some variability in the downstream extent of Olympic rainshadows and this is on the big side.
Another view of the rainshadow is the "storm total" precipitation (roughly the last two days) from the Camano Is. radar (see below). The rain shadow...a roughly circular region downstream of the Olympics...is clear evident, as is the heavy precipitation southeast of the Olympics
For the next 24-h it looks like the heaviest rain will hit SW Washington, the southern WA Cascades, and NW Oregon (see graphic), although it will be respectably wet everywhere.