Read this phrase in a blog. I think the basic meaning of the phrase 雨よ雪に変わってくれ is "The rain is changing into snow." But I don't understand the usage of よ in this case. Is it a particle? Or is it a typo?
It's a vocative particle, like the English vocative "O" in the following example:
O Rain! Please change into snow!
It sounds poetic or literary.
It's defined as 係助詞「よ」 in 集英社国語辞典:
I bolded the meaning, which is basically vocative.