Why do falling rain and blowing snow tend to create channels about 5-10cm across?

When I see rain fall it tends to be clustered into channels about 5-10cm across. When I see snow blowing it tends to do the same, and I can see that the channels are in the same direction as the as the wind.

My best guess is that the precipitation creates a drag on the moving air and it moves into the higher velocity channels that push the precipitation into the slower channels. The high velocity channels would be like the streams of water down a window, and the channels of precipitation would be the spaces between the streams.

Is this related to the sand ripples that are created orthogonal to the motion of the water?

Would snow more precisely be called 'precipitate' rather than 'precipitation'?