PREDICTING THE WEATHER

To take an umbrella or not? How we get those all-important forecasts

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The weather is unpredictable. So how is it that we can gather information and make predictions about what conditions on Earth will be like? Most weather phenomena occur as a result of the movement of warm and cold air masses. The borders between these bodies of air are known as 'fronts', and it's here that the most exciting weather, including precipitation and wind, occurs.

As a body of air passes across different types of terrain – such as over the oceans, low-lying areas or even mountainous regions – air temperature and moisture levels can change dramatically. When two air masses at different temperatures meet, the less dense, warmer of the two masses rises up and over the colder. Rising warm air creates an area of low pressure called a depression, which is associated with unsettled conditions like wind and rain.

We know how a frontal weather system will behave and which conditions it will produce down on the ground. Norwegian meteorologist Vilhelm Bjerknes first brought the idea of frontal weather systems to the fore in the early 20th century. Through his constant observation of weather conditions at frontal boundaries, he discovered that numerical calculations could be used to predict the weather. This model is still used today.