The fundamentals of precipitation

Learn about the fundamentals of precipitation and find out how it occurs.

Most people would rather prefer a sunny day over a gray and rainy day, but I think that we can all agree that we rely on getting some rain now and then. Follow along in this video where we will look at what precipitation is and what causes it.

A cloud consists of ice crystals and water droplets. In order for precipitation to come out of the cloud, the ice crystals must be in excess.

For that to happen, the temperature in the cloud must be at least -15 degrees Celsius. When the ice crystals become large enough, they fall as precipitation, either as rain, sleet or snow, depending on the temperature.

To understand cloud formation, one must know the difference between stable and unstable air. Air that is relatively warmer than the surface it moves over will be cooled down by the surface -  and therefore becomes heavier and more stable. Air that is cooler than the surface  - will be heated and therefore become lighter and rise into the air and therefore become unstable.

Stratiform clouds typically occur when stable warm air is forced to rise, for instance, by a mountainside.

Then there is cummuliform clouds. These will typically arise when cold air that is heated from below and becomes lighter – rises into the air and cools. Within cummuliform clouds there are different kinds, – most people being familiar with the cumulonimbus. This type of cloud is always involved when seeing tornadoes and tropical storms. Besides showers, there is a second type of precipitation. That is frontal precipitation.

Besides showers, there is a second type of precipitation. That is frontal precipitation.

When a shower typically has an estimated diameter of 500 meters to 100 kilometers, – the magnitude of the dynamic low pressure with associated fronts – is between 500 and 1,000 kilometers.

Weather fronts occur when warm and cold air meet, causing frictional resistance. We talk about warm and cold fronts – depending on who's winning. With cold fronts, the denser cold air pushes up the lighter warm air, causing the air to cool and form clouds.

On weather forecasts, these are illustrated with blue teeth.
With warm fronts, the warm air also rises and cools. But at the same time, the warm air pushes the cold air away as it slides up over the cold air. These are illustrated with a red semicircle.

The difference between the two is that the cold front is faster and more intense. Cold fronts usually bring cooler weather, clearing skies, and a sharp change in wind direction. The warm front, on the other hand, is slower and calmer.

Here, the precipitation can fall long before the front passes, – while it gets heavier as the front approaches, – followed by mild cloudy conditions between the warm and the cold front.

Course overview

Modules: 5
Completion time
Completion time: 25 minutes
Difficulty level
Difficulty level: Intermediate