gullywasher
Definitions
A heavy, drenching rainstorm capable of causing significant runoff.
A sudden, intense downpour that creates gullies in the ground.
Examples
We had to pull our car over to the side of the road because the sudden gullywasher made it impossible to see through the windshield.
The dry creek bed filled up in minutes after the afternoon gullywasher swept through the valley.