what makes the rain start?

Answer 1

Almost all the air around us is moist. That means that it contains water in the form of vapour. You can't see it because water vapour is a gas, but it's still water. Water can exist in three states; liquid (water), solid(ice) and gas(water vapour). Obviously, you can see and touch water and ice, but water vapour has no smell, you can't pick it up, and it's invisible. That doesn't mean that you can't feel it though.

Perhaps you can remember a hot and sticky day in summer, or a cold foggy day in winter, or even being in a hot shower full of steam? In each of those situations you will have felt water vapour all around you. If you stopped at really looked at that fog or steam you would have spotted millions and millions of tiny water droplets floating in the air. What you saw was the same process that makes clouds - millions of tiny water droplets condensing out of the air to form liquid water.

We've all seen fog and steam, but why does water condense out of air and become visible? Well, warm air can hold more water vapour than cool air, so if warm air starts to cool, it can no longer hold as much water vapour. The extra water vapour has to go somewhere, so it condenses out as water. So... cooling the air reduces it's ability to hold water vapour, and triggers the formation of water droplets. Remember that bit, 'cos it's very important.

Go outside and stare up at a cloud (not one right next to the Sun though - you don't want to go blind!). Watch that cloud for a while, especially it's edges. As you watch it, the edges will change, either growing larger or getting smaller. What you are seeing is cloud formation in action. As the cloud grows you are seeing more of those water droplets condensing out of the air, and as it shrinks, you are witnessing the droplets evaporating - changing from visible liquid water into invisible water vapour.

Now, it doesn't take a genius to point out that the clouds are usually a long way up, and not every cloud has rain pouring out of it. So, how does the formation of a cloud lead to actual rain?

To get rain, the water condensing in the clouds has to become heavy enough to fall to Earth. The tiny droplets just aren't heavy enough to fall. Just like fog or in the shower, they go whichever way the wind and eddy currents blow them, or they just hang there, suspended in the air.

To become heavier, the droplets need to grow into drops. To do this they have to acquire more water and become larger. Some will collide with other droplets and become larger, and others will grow as water condenses out the air directly into the droplet. Others will grow by both methods. It's a bit like watching drops of rain water on a window - small drops fall, they join with other small drops, become larger drops, and so on. In the right clouds, this process will be happening to millions of tiny droplets, all growing at the same time, but at different speeds.

Eventually, if the droplets keep growing, they will reach a mass where they can't stay floating in the cloud because they are too heavy - and will start to fall. Some may get caught in upward blowing winds and get blown back into the clouds for a while, but once they are heavy enough to overcome the force of the wind, they will fall to earth - as rain! It will keep raining as long as the conditions are right to make the clouds and let the water droplets grow heavy enough to fall.

So, there you go - now you know what a cloud is, and how it creates rain.

Answer 2

The evaporation which rises , collects in the clouds. When the weight is too much, It must return to earth in the form of rain. To have the condensation come back to earth in the form of rain, the barometer must fall.

Answer 3

It all comes from the water cycle. First, water eveporates into the sky from mountains, rivers, streams or even ground water. Thats why we have that mist or fogg sometimes. Then the water vapor gets carried to the clouds and if its too heavy in one of the clouds it finally rains.

Answer 4

I think what does it is that the clouds get over-saturated with water vapors that eventually condense due to the temperature difference between them and the air bellow them

Answer 5

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Answer 6

Hanging out the washing.

Answer 7

The guard waves his flag, or is that a train?

Answer 8

the clouds get heavy

Answer 9

when the clouds are full of water

Answer 10

condensation in clouds.