"First one has to love nature with all ones heart and soul, and be able to study and admire it for hours on end. Everything is in nature. A plant, a leaf, a blade of grass, should be the subjects of infinite and fruitful meditations; for the artist, a cloud floating in the sky has form, and the form affords him joy, helps him think." William Bouguereau
Below is a link to a short explanation on cloud formations that may help you in landscape painting.
It is better to know what you are painting then to always guess at what could be happening. I do that a lot, but I've bumped up against a wall on some new projects so I'm having to go back and study cloud formations so I can invent some landscapes in the back of paintings I'm working on.