The boating term "restricted visibility" means: Any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.
And the more you boat, chances are you will be caught in an element that will restrict your visibility.
However, if you want to better your chances of not being caught in a rainstorm, hail, snow, fog, etc. - check your local marine forecast before and while you're on the water.