Other forms: rainstorms
When clouds roll in and drops of water start to pour from the sky, it's a rainstorm. If the weather report predicts a rainstorm, you'd better grab your umbrella!
You could also call a rainstorm a downpour or a cloudburst — it's a weather event involving heavier rain than a rain shower or drizzle. Certain unstable air conditions sometimes cause a rainstorm to turn into a thunderstorm. A farmer in the midst of a dry, hot summer is likely hoping for a rainstorm, but if you're excited about an outdoor family reunion next weekend, a rainstorm in the forecast will be very disappointing.