Rain can occur when there is more heat energy in the atmosphere, making it less stable, especially when the surface is warmed and there is relatively cool air above.
This is more likely in the afternoon and early evening when the sun has been shining on the earth all day.
Given the right meteorological conditions, this instability causes convection, and water vapour starts to rise. Increased moisture in the air can bring on showers and even thunderstorms. The effect is enhanced because air can hold more water when it's warmer.
It is compounded by evaporation, which typically happens during the day, taking liquid water from the soil, plants, lakes, rivers and oceans into the air.
The phenomena is more pronounced during summer, but changes during winter when rain is often heaviest overnight.
Cloud-tops lose their energy into space, making them cooler relative to the surface. They lose their ability to hold the same amount of moisture and, like wringing out a sponge, water falls to the ground as rain.
While showers are another type of rainfall, they involve slightly different processes.
Rain is commonly associated with fronts and troughs where moist air is forced upwards by convection. This is generally on a large scale, often over hundreds of kilometres, and rain comes from 'flat' stratus clouds. As a result, rain is usually steady and widespread, easily lasting hours or days.
The most well-known rain source in Australia is the Northwest Rainband, a line of cloud that extends from northern WA through to south-eastern Australia, bringing rain to inland parts of South Australia, Victoria and NSW.
Showers are also closely linked to convection, although they occur in heavier and much more patchy bursts. Showers come from cumulus and cumulonimbus clouds that extend vertically into the troposphere, and can be associated with thunderstorms. Showers will often only last a few minutes, but can last longer if they become slow-moving and can lead to flash flooding.
Showers occur at all times of the year, but tend to be heavier during summer, due to the greater amount of moisture in the air from heating.
