Santa Cruz lighthouse in pencil

It's been a while since I have painted due to crazy schedules, so with some free time, I find myself at the beach.  The only time I painted a seascape was a couple of years ages with a Watercolor of Sea and Sky and that was from a photo. As I am sitting on the beach, I decide that a pencil sketch is going to work better than a watercolor due to the sand getting all over everything.
 The morning sun was shining from behind the lighthouse, just starting to burn through the marine layer. The waves are a particular challenge, and how can I differentiate between blue sky and grey clouds when I just have a pencil? I will need to redo this in watercolor...