Atmospheric complexity: Why is my weather forecast inaccurate?

Meteorologists use some of the world’s most powerful super-computers to produce weather forecasts. So why is my forecast inaccurate?

Super-computers incorporate a vast amount of data and perform trillions of calculations per second to help us predict how the weather will change in the coming days. Despite significant technological and scientific breakthroughs, there are still limits.

Due to the chaotic complexity of the atmosphere, detailed weather forecasts tend to only be reliable for up to five days or so. The atmosphere is changing all the time, so predictions become less reliable the further you get into the future.

Weather models have as high a resolution as 1 km, which means the computers break down the Earth into tiny 1 km-space grid points to resolve the atmospheric conditions.

While this may seem tiny across the planet, it's still gives room for error for small-scale weather events, such as localised showers.

In every case, Meteorologists apply their expertise to analyse the weather model's output, in order to provide the most accurate forecast. Even the best models in the world aren't always correct!

Being an island in the British Isles, with a maritime climate and at our latitude, this means our weather can be highly variable; unsettled weather from the west, colder air from the north, and warmer air from the south, for example.

Short-term forecasts cover a period of 24 hours up to three days. We see these on the TV every day. They are generated using synoptic meteorology – current atmospheric observations – and numerical models.

If the weather conditions are particularly complex, there can still be a degree of error even within the five-day period. High pressure is relatively predictable due to its stable nature, but low pressure is more tricky.

Medium-range forecasts cover between three and 10 days with long-term forecasts covering periods over 10 days away. Both are generated by using weather ensemble models to create a weather trend.

Long-term forecasts are becoming increasingly popular in media. Sometimes you even get explicit forecasts of temperature, rain and weather for several months in advance, though this level of detail so far out is likely to be inaccurate.

So instead, often conditions across trends are described as wetter or drier, warmer or cooler with no specific information.

Each day, we provide you with a tailored Breakfast Brief to cover the day's weather, in addition to a Weather Trend three times a week. You can also find information by searching your location inside the app, or taking a look at the WeatherRadar.