A typical raindrop is about 2 mm in diameter. They rarely exceed 5 mm because large drops become deformed as they fall through the air, and ultimately disintegrate into a number of smaller ones, which puts an upper limit on the drop size.
Moreover, the "tearshaped" drop so beloved of artists and cartoonists does not exist in nature; very small drizzle drops are spherical, while the larger raindrops take on a shape rather like a plum pudding or a bun-burger, flattened at the bottom because the air pressure is greater there than on the sides.
But have you ever wondered why rain should fall from certain clouds, and not from others? Clearly something happens to a cloud to make it suddenly decide to empty itself upon us at the moment of greatest inconvenience.
And again the answer lies in the size of the drops of water, this time the tiny droplets that make up the cloud. If they are so small and light that the air around them offers great resistance to their movement, they "float" in the atmosphere rather than drifting down to earth, supported by the gentle upward currents common in the vicinity of cloud. But if they are big, they fall as rain.
There are two ways in which clouds manage to produce the bigger and heavier drops that must succumb to gravity. The first is called the coalescence process, and comes about as the tiny droplets of water collide with each other, and merge to form larger ones.
As the drops get bigger they drift downwards, and since those of different sizes fall at different speeds, the tendency for collision increases. The result is larger and larger drops, and if the cloud is thick enough the drops become sufficiently big to fall as rain. The other way in which raindrops are formed is called the ice-crystal process, and it occurs in clouds where the temperature is below freezing point. When ice-crystals and water droplets coexist in a cloud, then, by one of nature's wonderful tricks, the ice-crystals grow at the expense of the water droplets by attracting their moisture from them.
As the ice-crystals grow in this way, they begin to fall through the cloud and collide with other ice-crystals to form snowflakes. When the temperature at ground level is less than about 4 C, the flakes survive in their crystalline form and drift slowly down to earth as snow. On the other hand, if it is relatively warm at ground level - as it usually is in Ireland - the snowflakes melt and fall as rain.