idiom which means rain heavily
Solution 1:
"And then mother nature became furious. The sky turned gray and it started lashing down."
"lash down" - (Of rain) to fall very heavily.
- "torrential rain was lashing down"
- "It's been lashing down for the last hour or so."
- "It's dry at the moment, but with how dark those clouds are it looks like it could lash down at any moment."