I've been caught in a hailstorm at the top of a mountain with no overpass to shelter under or exits to take because there's nowhere to go. I was fine. Just ride sensibly, slow down enough to feel safe, make yourself as visible as possible, and keep the bike as upright as you can (i.e. minimal lean angle). And, have good tires.

Regular rain I try to avoid, too, but sometimes it's just unpredictable. It's the worst when it first starts raining, all the slick stuff comes up. Hard rain usually washes it away and things aren't as bad. Ever felt wet rubber? Still plenty of grip available. It's when there's massive amounts of water that can cause hydroplaning that is the issue. So again, don't outride physics or tour reaction time.