What does "wet weather in my soul" mean?

Question

A psychologist tells of how his 5-year-old daughter taught him something that made him change:

"The notion of a Positive Psychology movement began at a moment in time a few months after I had been elected President of the American Psychological Association. It took place in my garden while I was weeding with my five-year old daughter, Nikki. I have to confess that even though I write books about children, I'm really not all that good with them. I am goal-oriented and time-urgent and when I'm weeding in the garden, I'm actually trying to get the weeding done. Nikki, however, was throwing weeds into the air and dancing around. I yelled at her. She walked away, came back, and said, "Daddy, I want to talk to you."

"Yes, Nikki?"

"Daddy, do you remember before my fifth birthday? From the time I was three to the time I was five, I was a whiner. I whined every day. When I turned five, I decided not to whine anymore. That was the hardest thing I've ever done. And if I can stop whining, you can stop being such a grouch."

This was for me an epiphany, nothing less. I learned something about Nikki, something about raising kids, something about myself, and a great deal about my profession."

"Raising children, I realized, is more than fixing what is wrong with them. It is about identifying and nurturing their strongest qualities, what they own and are best at, and helping them find niches in which they can best live out these positive qualities.

As for my own life, Nikki hit the nail right on the head. I was a grouch. I had spent fifty years mostly enduring wet weather in my soul, and the last ten years being a nimbus cloud in a household of sunshine. Any good fortune I had was probably not due to my grouchiness, but in spite of it. In that moment, I resolved to change."

What do the boldface parts mean?

Answer 1

It's just figure of speech; wet weather (rain) is often associated with misery; also, nimbus clouds can cause large rain showers.

The speaker contrasts this to the fair weather (sunshine) in the rest of his family; sunshine is often associated with happiness.

Answer 2

A common thing to say about a rainy day with dark skies, especially in the cities in countries where there is an awful lot of rain, is that it is a gloomy day, and "gloom" is often used figuratively to express a lack of optimism and cheer. So, "wet weather", and the darkened skies it suggests, could here be a figurative allusion to depression, as it is wet weather in his soul.

A farmer, or a person living in a desert region, might have a very different attitude towards rain :)