On a commute, I'll watch the radar "movie" and try to time a 45 minute gap for my 45 minute ride. Usually works, although sometimes it'll rain.


If I'm on a longer, but still informal, ride, I like to leave a 30 minute window after getting home before the rain hits.


On a formal ride (century, brevet, or the like), unless it's going to be too bad to ride, break out the raincoat and make sure there's something to wipe my glasses with in a dry bag for when it stops.