Why is rainfall uniform even though clouds exist in lumps? Since clouds exist in lumps and are non-uniformly distributed, one would expect rainfall to be non-uniform as well. But as far as I can tell, rainfall is more or less uniform over a large region.
I suspect that turbulence might be at play here and cause the dispersal of raindrops, but I'm not really sure.
EDIT: I agree that rainfall is non-uniform as well but the non-uniformity of cloud distribution doesn't seem to commensurate with the rainfall. In other words, the cloud distribution appears to be much more uneven than the rainfall, but maybe that's just an illusion. Perhaps a better question might be, "is rainfall as non-uniform as the cloud distribution? If not, then why?".
 A: Rainfall uniformity is dependent on the cloud structure that gives rise to it. For cold fronts and thunderstorms, the rain-causing regions are squeezed together and you get extremely dense rain in one area and almost nothing right nearby. Highly nonuniform.
For warm fronts, the rain clouds are spread out over a far greater area and the resulting rainfall densities are much more uniform.
A: Clouds move with the wind. It can be a little like your sprinkler watering a moving spot, and eventually covering the whole yard.
A: When my region gets days of slow, steady rain from a broad layer of stratus clouds, there isn't much variation: everybody gets days of rain.
But in the summertime, most of my rain comes from cumulus clouds.  These "fair weather" clouds happen when a humid layer of air near the ground heats up faster than the air at higher altitudes.  Eventually the warm air breaks into the cool layer and starts to rise, making puffy clouds, thunderheads, or tornado-bearing storms, depending on ... well, depending on the weather.  Our topography here isn't very complicated, so the locations of these storms can't really be predicted until they've started to happen.  Once they start they can be very localized.  It's not uncommon for me to get caught in a storm so hard that I have to pull off of the road and wait, then drive two or three miles and find that the roads are completely dry.  Two weeks ago I drove fifteen miles to go on a hike, and drove through such a storm: sunny and dry at my house, dark and rainy partway there, sunny and dry at the trailhead.  I did get rained on while I was walking, about an hour later, but I think my house stayed dry.
Many years ago I was driving across the New Mexico desert on a bright summer day, and crested a hill where I could see many miles in every direction. The sky was full of regularly-spaced puffy cumulus clouds, hundreds of them. Exactly one had a grey tail of rain underneath it.  I can't say how intense it was at the ground, because it never rained on the highway.
Rainfall may be uniform on average, but rainstorms have as much variation as clouds do.
