Something told me that I should go to the Grand Forest Hilltop and look at the Olympics this afternoon. I didn’t expect to see this cloud formation, but when I saw it it was no mystery why it is there, while the rest of the sky is cloudless under dry high pressure.
Were having cold outflow winds this week. As the dry interior air from the BC interior exits the Fraser Valley and crosses the Salish Sea, it picks up moisture from the relatively warm (about 50 °F) salt water. When that wind hits the Olympic Mountains, some of it is forced to rise and cool, causing the moisture to condense and form that cloud. Sometimes the effect is profound enough to cause an area of snow to fall on that region.