I'll wait out a hail storm or a thunderstorm. These things usually only come in the afternoons around here. In the morning, I'll ride regardless of the forecast and just be prepared.

A little rain never hurt anyone. Thunder and hail can potentially hurt, but they're usually gone in 20-30 minutes, so I'll find a nice place to just wait the storms out. If it gets real bad, I can throw the bike on a bus.