Thanks for your question! I’m usually asked when is the “best” weather on the Oregon Coast or when to plan a trip when it’s not cloudy or foggy and I have to try to explain that sunny skies are not necessarily the best and certainly are not the most typical or interesting of the climatic conditions the coast is famous for. Unfortunately, predicting fog is equally challenging and the coast experiences fog in all seasons including summer when hot inland temperatures can trap heavy marine air west of the Coast Range.
That said, I feel like the most climatically interesting times of year are generally early fall (October) and late spring (May). We have a variety of atmospheric conditions that can occur including fog, dramatic cloud formations, a hazy marine layer and varied weather systems that produce ever changing sunlit scenes with ominous skies. I think of great clouds and sunbreaks as among the top conditions for exciting photography along with fog and all of the varying denseness possibilities of the marine layer.
Average temperatures are almost identical between these two months with highs in the low 60s and lows in the mid 40s. October is slightly wetter on average and that increased chance of humidity would suggest there is an increased chance of fog on average. What I love about May in regards to landscape photography is fresh spring growth that represents all shades of green and blooming shrubs that can add color and texture to scenes.
Come prepared for whatever conditions Mother Nature presents and I hope you find the exciting light and atmospheric conditions that make your photos better and more interesting than any boring blue sky day could offer.