Before we can make a weather forecast there are number of steps we have to take, including collecting and assimilating data.
Observations are vital to the process of creating forecasts. Every day we receive around 500,000 observations recording the atmospheric conditions around the world. The Met Office is responsible for maintaining the observation network over the UK and contributes to the funding of weather satellites and buoys. Observations made 24 hours a day - across the globe - are passed to the world's major weather forecasting centres, including us.
Data sources are always changing and improving. They now include observations of the atmosphere taken from more than 36,000 km above the Earth, and of the ocean taken from 2,000 m below sea-level.
Each day, we receive and use around half a million observations of temperature; pressure; wind speed and direction; humidity, and many others which we use for the starting conditions of our weather forecast model.
Even with the many observations we receive we do not have enough information to tell us what the atmosphere is doing at all points on and above the Earth's surface.
There are large areas of ocean, inaccessible regions on land and remote levels in the atmosphere where we have very few, or no, observations. To fill in the 'gaps' we can combine what observations we do have with forecasts of what we expect the conditions in the atmosphere to be. This is a process called data assimilation and gives us our best estimate of the current state of the atmosphere - the first step in producing a weather forecast.
Without data assimilation, any attempt to produce reliable forecasts is almost certain to end in failure.
Numerical model of the atmosphere
Even tiny changes in the atmospheric conditions can lead to drastically different weather patterns after only a short time, so it is vital that the current state of the atmosphere is represented as accurately as possible. This process is highly mathematical and takes the supercomputer longer to accurately estimate the current atmospheric state than it does to actually make the forecast.
Our scientists are continually working to improve our understanding of atmospheric processes, so they can be better simulated in our forecast model, the Unified Model, and ultimately, lead to more accurate forecasts.
Met Office supercomputers
Each numerical weather prediction produced involves billions of mathematical calculations. Powerful supercomputers are required to be able to do these calculations as quickly as possible.