Thank you for your question, Lorna.  Without close up, clear photos of both the needles and the entire tree, we cannot diagnose whether it might be a blight (https://hortsense.cahnrs.wsu.edu/fact-sheet/true-cedar-cedrus-needle-blight/) or whether the drop is a response to our changing climate, together with heat, water (too much or too little), or something else.  You can attach photos to a response, or take them, as well as a branch showing the drop, to either the Washington County (https://extension.oregonstate.edu/washington) or Clackamas County Extension office (https://extension.oregonstate.edu/clackamas), when Master Gardeners are there to examine them.  I hope this is helpful.