It's okay to set up the mood/scene a little but, and it's a big but, you are dealing with people who have an extremely short attention span. You also have a verly limited amount of space, so it's not good to waste it.
Also you have to think that they may not be able to recreate what you have, same with physical descriptions of people, they may not be able to match it, so it's better to capture the essence of the character rather than physical looks.
A quick and dirty example of an opening scene that would capture both your mountains and sky and still cut right to the chase.
EXT. MOUTAINS - DAWN Sets the scene
A hiker in full gear, mid 30's, treks up the side of the mountain, a carved walking stick as his companion. Who's in the scene.
Action.
A rustling in a large bush draws his attention, he investigates, dropping his pack to the ground.
He reaches for the bush--
A bear jumps out, roaring at the intruder.
It knocks the unsuspecting hiker to the ground, pinning him against a walk.
The anxious hiker crawls a bit. The bear, matted and nasty looking, brings down his heavy paw with one big swipe finishing off the hiker.
It surveys the area, then grabs the hiker and retreats back into the bush to enjoy its sinful meal unseen.
Hope it helps.