Mountains and clouds in one frame are a test for any camera: expose for the land and the sky burns out, expose for the sky and the land goes dark (sample tutorial).
Make a sky mask, then pull its highlights down and its whites a little lower. Because the mask covers only the sky, the mountains do not change.
Finish with a light Punch look on the whole photo, and check the reflection in the lake: it should be a little darker than the sky above it.