How does the humidity factor into rain?
Humidity is a measure of the amount of water vapor in the air, not the total amount of vapor and liquid (rain). For clouds to form, and rain to start, the air does have to reach 100% relative humidity, but only where the clouds are forming or where the rain is coming from. This normally happens when the air rises and cools. Here’s a bit of trivia for you, often rain will be falling from clouds where the humidity is 100% into air with a lower humidity. Some water from the rain evaporates into the air it’s falling through, increasing the humidity, but usually not enough to bring the humidity up to 100%.
