Hi, I got this reply from a very nice person on Booksleuth
"Right after asking you for more details a name popped into my head! In the fifties British Sci Fi writers were big on end of the world books and although I no longer have it in my collection, years ago, I had a copy of "White August " by John Boland.As much as I can recall it was an "end of the world when an attempt at weather control goes wrong" book and snow starts falling and will not stop.I had a quick run around the web on Google but as this book was published in 1955 I could not find any book reviews to check the " green sky and snow " part but maybe someone out there who owns a copy will mail in.Anyway I may have given you the book you're after so fingers crossed. "