What kind of weather conditions must artificial rainfall have in drought?

The first is the water vapor condition.

The second condition is that there must be upward movement, which is equivalent to the machining process. Because the upward movement brings water vapor to high altitude and condenses to form clouds, it can produce precipitation, so the upward movement is essential.

The third condition is an appropriate amount of condensation nuclei, because the condensation of water vapor requires an adherent. Without condensation nuclei, water vapor cannot condense effectively. If there are not enough ice crystals in this cloud in nature, because the water droplets in the cloud are so small that they can't fall down in the air for a long time, then there will be only clouds without rain. At this time, if silver iodide particles are sown in this cloud, many ice crystals can be produced. The water on the water droplets in the cloud is quickly transformed into these artificial ice crystals through evaporation and condensation, which makes the ice crystals grow rapidly and produce snowfall. If the ground temperature is high, the snow will melt and merge into water droplets during the falling process, and eventually become rain. This is artificial precipitation enhancement.