system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does heavy rain come down in "sheets"?

Here in NC watching the rain come down from Florence (I'm safe), and I'm curious about what causes the wave-like pattern of alternating heavy and lighter rain that comes in semi-regular intervals of a few seconds or less apart. We've all seen this phenomenon, especially at night on concrete under artificial light, where they travel in very regular waves like ripples in a bathtub.
gpt
The sheets of rain are following the pattern of the guessing wind.

As a gust passes through, it will move around the droplets of rain falling - blowing some ahead of it, and slowing down the fall of some by blowing them upwards into the air again. Once the first has passed the rain 'caught' by it will then all fall at once in a slightly heavier sheet.