What are the signs before it rains?

Frogs chirping, swallows flying low, etc. They are all signs before the rain, and the accuracy is quite high. There are several others:

Ants crossing the road-ants digging holes in the ground think that the holes will be flooded when it rains, that is, they will run away before it rains. Earthworms come out of the hole-the ground is wet and soft, and earthworms will climb out of the ground, which indicates that it will rain. Before the rain, there were signs of mosquitoes swarming, rain ants swarming and cats washing their faces.

general situation

When it rains, how do these small water droplets increase their volume to more than 1 10,000 times? Mainly by two means: one is condensation, and the other is the increase of cloud droplet collision. In the initial stage of raindrop formation, cloud droplets mainly condense and condense themselves by constantly absorbing water vapor around the cloud.

If the water vapor in the cloud can be constantly replenished and replenished, so that the surface of the cloud droplets is often in a state of supersaturation, then this condensation process will continue, making the cloud droplets grow and become raindrops. However, sometimes the water vapor content in the cloud is limited, and in the same cloud, the water vapor is often in short supply, so it is impossible to make every cloud droplet grow into a larger raindrop, and some smaller cloud droplets have to be merged into a larger cloud droplet. If there are water droplets and ice crystals in the cloud, the process of condensation and sublimation will be greatly accelerated.