system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does rain fall in storms and not a little throughout a day?

Why does rain seem to fall all at once in storms and not just slowly drip down a few drops at the time throughout a day?
gpt
Warm air can hold the moisture indefinitely, but when it collides with a mass of cold air the moisture falls as rain.

Some places do have a near-constant mixture of warm humid air and cold dry air that will produce long, slow rain systems.

Most of the rest of the world will only experience this periodically - you’ll either be under the humid air or under the cold air, not directly under the boundary where the storms are.

These boundaries can persist for days and sweep across entire continents as one air mass overpowers another, but they’ll only be over any particular location for a few hours.