It all depends...
Depending on how late the run is, beach temperatures, river temps, wind direction, if a thermocline is present, weather patterns, and even barometric pressure; the run can be anytime from June until September.
Usually, a few days to a week with an easternly wind will cause the warm beach water to move out with a coldwater updwelling replacing it and stage fish off the river mouths and piers. If it rains and colder air temps are present you are in business. If the water is about 55-60 deg, then most fish will come in to the shallower areas. Depending on how warm the river is, the fish will either run it the water temp is in confluence with beach temps or just stage and wait till temps are ideal. Sometimes warm water and hot summers keep fish from running until fall or even at all. This is why it can sometimes be a last minute trip to plan.
Be sure to have surf patterns and river patterns. Skamania are know to feed on insects like bees, grasshoppers and of course anything hatching on top. They also eat nymphs, baitfish, crayfish and other interesting things. In the surf, alewives patterns are best. I have many, email me for details. Sometimes fishing the surf is far more productive.
Lets plan a trip Juro, I can meet up with you if you would like?