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Am receiving Oregon traffic on 154.935 in Port Townsend. I vote for the fog helping rather than VHF ducting. I haven't checked VHF low

-m

This seems to be a fairly good article
http://www.ham-shack.com/propagation.html
I'm a 'weather nut'. The main cause is said to be the inversion layer. Some of the effects of inversions are fog and the trapping of pollutants in the lower atmosphere. Fog basically occurs when the dewpoint temperature and the drybulb temperature are very close to each other, thus the air mass of fog is fully saturated or near or at 100% humidity. There are frequencies at which a saturated air mass, like rain, fog, snow and the like, obscure or block electromagnetic radiation, such as light and the lower-frequency radio waves.