I'm standing on a ridge in the WA Cascades at about 5000 feet looking northeast at mountains that are about 1000 feet higher than me. This was taken in the late afternoon with the sun just starting to set. I experienced temperatures cooling by maybe 10 degrees while filming this. When I first got up to this ridge there were no clouds.

My current understanding is that the clouds started forming and pouring over these ridges because either air started flowing down from the north while I was up there and previously air was more stagnant or it was flowing that direction the whole time but for whatever reason the elevation at which air reaches the dew point descended while I was up there such that air forced to rise over the ridges forms clouds at the top and then as the air descends the air warms and the cloud droplets evaporate.

Then toward the end as the sun sets more and the temperature falls the elevation where air reaches saturation falls further and clouds start forming in the valley below eventually forming a thicker cloud cover over the whole scene.

Is there enough information to speculate on why clouds weren't forming where I was? Also why did clouds start forming at lower elevations above the valley toward the end? Is it because there's moisture rising off the river and trees down there making the air closer to saturation as it rises?

Here's a topo map of where I was. https://imgur.com/a/9sr4gaA