If it's possible to avoid something, you can describe it as evitable. Unless you live in Antarctica or some deserts, rain is definitely not evitable.
The antonym of this word, inevitable, is far more common, and etymologists are fairly certain it came first. Today, it's rare to hear something described as evitable, but feel free to use it for anything that can be dodged or averted. Meeting your exact look-alike is probably evitable, unless you're an identical twin. Some people would say the only things that aren't evitable are death and taxes.