Yes, September before they close the season. The season is usually closed by quota, meaning the combined sport and commercial catch. In most years this does not make it thru September but this year is so heavy of a return that they are going by calendar date. If Ryan's sources are good (and they should be based on his major at UW) then we should be able to go by calendar year again next year.
Even still, I would be prepared to beat the quota just to be safe. Short answer - first two weeks in Sept.
This happens to co-incide with great steelhead fishing as well, there are dozens of rivers to choose from.
If we got a fair number of parties interested then splitting a rental car would be cheap enough too.
I hope this comes together!