Fair weather friends means something that can only be used in good weather.
Have you ever had such friends?---Yes,once. She was my best friend, but tuned a fair weather friends.
And, to her, I also tuned a fair weather friend from her best one.
She was my friend when we were junior high school students.
We talked a lot about boys we liked, teachers we didn't like, parents we hated.
But when we became adults we had a quarrel.
She had cheated with some other boys though she had a good boy friend.
I scolded her to stop that but she was annoyed with that.
She said, "OK, enough."
And-- we had broke up since then.
Nowadays, I sometimes meet her with our mutual friend.
But I feel we'll go back to be friends we used to.