Some conifers, like pines and arborvitae, often lose their inner needles in the fall. It's called seasonal needle drop. However, Douglas Fir does not usually do this. It's possible you have a needle cast fungal disease on the tree. Unfortunately, the only way to positively diagnose this is by getting a magnified look at the underside of the needles. It would be best seen on a needle that is just turning yellow. For Swiss needle cast, if you can, use your camera to focus in on the underside and take a look for the presence of black spots on either side of the needles' rib. See photo below. http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=1&SubCatId=3&PlantDefId=11&ProblemId=362  Another fungal disease, Rhabdocline needle cast disease, looks very similar until seen much closer. http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=1&SubCatId=3&PlantDefId=11&ProblemId=359 Again, see the photo below. The needles will be mottled with rust colored areas.

It is possible that something environmental is the cause of the tree's problems. It's impossible to tell without looking at the needles. Does your phone camera take good magnified views? If so, you could try to send more photos. Otherwise, I suggest you contact your county's Extension service. Skamania County Extension will diagnose your plant or pest problem for free.