Watching NOAA put up information out in the links above the drop puzzled me so I went and dug up a couple of old friends who know way more than I do about such things. Bottom line is despite all the rain the Chehalis Basin is still recovering from the drought. While for us the ground is soaked it is at the surface area. Deeper into the ground the ground is still drinking water as the drought dried things out much more & deeper than normal. Also the shallow aquafers are still filling which is normal as some ( well many ) such as the one that feeds Dry Bed Creek do not flow at a continuous volume until the aquafer is full.

So the rapid stream flow drop as rain stops is normal. The huge drops forecasted should and will disappear once the ground water & ground itself get fully charged. Evidently the drought effected things much more than many thought. Think of it this way. The low summer flows really impact fish particularly Coho. If the ground got as low as it appears then most of the small creeks and over summering areas took a hit for Coho production. Time will tell but I doubt words like small, minimal, minor will be used to describe it.
Dazed and confused.............the fog is closing in