The third process, that which makes the rain decide to fall, is the question which occupies mans attention the most, because of his reliance on water. I have no suggestions on this, other than if we fail to understand why the clouds stay up, we may never understand why the rain falls.
My concern is the question of what keeps the clouds up. To clarify the issue we should look at the situation of a severe storm, or hurricane. These storms can release rainfall of 900 mm over a period of 36 hours. They probably are creating more cloud as they are dropping rain, but at any one time it should be possible to calculate the mass of water in the air, consisting of both falling rain and cloud particles. Lets assume an amount of half the rainfall, say 450mm. Lets also assume an average sea level pressure under normal conditions of 1013 millibar. The sea level pressure would be around 1060 millibar if we add the mass of liquid water within the air.
As we are all well aware, storms of this nature cause, or are caused by, extremely low air pressure, probably around 870 millibar. So we really have two impossible situations. The first is that storm clouds containing probably millions of tons of liquid water can stay up in the air at all, and secondly that a barometer will clearly show that this extremely heavy, water laden air, weighs far less than the air on a clear day. The reason I use a hurricane for this discussion is because the videos or satellite images we see, clearly show the rotating nature of the storm. Indeed it is for this reason that they are called cyclones, or cyclonic conditions.
I suggest that what we have here is another example of Anomalous Gravitational Effects. A rotating ring (of air and water), with a calm clear center, with air weighing less than it should. Electrical activity in the form of thunderstorms is usually also involved.
It is interesting to note that in a clear weather situation, the air pressure is higher than average, that is, the air is heavier than air that is full of liquid water. It would seem to me that the idea of anti-gravity, which science denies, may well be a normal part of our existence, without which we could not survive.
Storm surges are also of interest here. Cyclones or Hurricanes tend to create damaging storm surges at times. The sea level can rise a few meters above the normal highest tide below the cyclone. These surges do not appear to travel at the speed of the wind, rather they move at the velocity of the storm across the planet. The spinning mass of the water in the sky creates a lift in the water below it which is far in excess of what the lowered barometric air pressure can account for. Several times I have seen eye witness reports of flying saucers hovering above water. These people describe the surface of the water rising visibly below the craft.
It appears to me that a cyclone or hurricane may be a vast, naturally occurring, antigravity machine.