The top image above shows migrants arriving this morning and as time progresses the image returns become more faint as birds land. This is the exact opposite progression of the liftoff we see in the evening.
Ann Nightingale of Victoria, B.C. mentioned on BIRDBAND another radar image source for that region that looks really good. It is from the University of Washington. Again, the top image shows birds arriving and the second shows the image fading as birds land. For west coast birders I've also seen this pattern in the central valley of California.
Here are those images:
I'm going to go watch the White-throated Sparrows under my feeder for a while...