A good day

The sun came out today after two or three days of rain and grey.

And it's a good day.  I feel good today.  I feel like I can get things done. 

I don't get it.  Why is that?

Why is the equation - sunny day = good day.  Cloudy day != not as good day.  Perhaps it's also November.

I know every day is a good day - I just don't get it.  Maybe I need to move to Arizona/New Mexico/Southern California.