Question: Let's say you're on top of the Grand -- or anything else for that matter -- and you realize that you're above something like that. Do you descend through it or try and ride the top for a while and descend after it has passed... maybe? And with darkness coming on? Or do those clouds just say foggy and chilly? Rookie wants to know.
It depends. It is rare that the weather on top of a mountain is clearer (or better) than down low. When it does happen (I've experienced this most often on a Pacific NW volcano) it often indicates the weather is pretty good in general and there is only some low level drizzle or fog. In that case you can either stay on top and enjoy the view, or descend into the fog, no rush.
During stormy weather, a sudden clearing may also occur when you are on top of any peak. Often this is not a cause for celebration, it just means you are about to be swallowed by an approaching cloud and should descend ASAP.