"This term is used throughout the Midland, Southern and Western United States. Allan A. Metcalf's 2000 book How We Talk: American Regional English Today notes "there are gully washers throughout the South and South Midlands, and this is one Southern term that is well-known in the central Midwest as well, as far north as Nebraska, Iowa, and Wisconsin, and as far west as Colorado. But there aren't any gully washers in New England or the northernmost states, and the word is rare on the Pacific coast." Wiki - "Gully washer"
So then I got ta thinkin', I bet lots of people have lots of different ways to refer to heavy downpours....
|"Rain Storm" by Cotton Valent - http://cottonvalent.deviantart.com/art/Rain-Storm-122143459|