How do you deal with a boss who is always in a bad mood?

My boss is a nice person but he is always in a bad mood. Most days he comes into the office already in a bad mood. On a rare occasion he will be in a good mood at the start of the day but goes from zero to sour pretty quick.

My work environment is very fast moving and high stress. He hasn’t been here as long as me and I think part of the problem is that he inherited a lot of stuff that he wasn’t really expecting. I have offered to help him but that usually doesn’t get anywhere and if I ask him about specific things he snaps at me.

I am not really sure how to deal with this because I feel like it gets worse every day and it really makes me not want to be here anymore. What do I do? Who should I talk to and how is the best way to approach my concern.