Last year, weren't we all talking about planting onions in October? All I can find is info on planting them in the spring. Only the ones I planted last year have gotten any size so far, though hopefully our summer heat isn't over yet.
Steve Solomon has a book, Growing Vegetables West of the Cascades, that is a wealth of information. Your library might very likely have it since it's such a classic. He addresses the idea of growing overwintering onions as follows: "Short-day varieties for the North are sown in late summer, overwinter, and mature in June...are the easiest of all bulbing types to grow, though care has to be taken to obtain good germination when sowing onion seed in the heat of August..." He writes. " Territorial Seed is very interested in overwintering bulb onions...West Coast also..avoid varieties bred for southern latitudes, often called Grano or Granex."
I haven't tried it but have often considered it. Please post your experiences with this if you try it because it'll be great info.
Steve Solomon's info should be especially well suited for you. His original 5 acres in Oregon was in Lorane, just 25 miles from you. He was my neighbor for a couple of years.