Creating forecasts — First Steps

Before we can make a weather forecast, observations must first be collected from all over the globe so that we can make a good estimate of the current atmospheric conditions. Then, by applying our understanding of the atmosphere, oceans and land surface, we can predict how those atmospheric conditions will change with time. We do this by running complex simulations on a supercomputer.

Observations

Observations are vital to the process of creating forecasts. Data sources are always changing and improving and now include observations of the atmosphere taken from over 36,000 kilometres above the Earth, and of the ocean taken from 2,000 metres below sea level. Currently the main sources of observations are:

• weather satellites
• balloon profiles
• surface data
• marine data
• aircraft observations

The Met Office is responsible for maintaining the observation network over the United Kingdom and contributes to the funding of weather satellites and buoys. Observations made 24 hours a day, all across the globe, are passed to the world's major weather forecasting centres.

Each day, the Met Office receives and uses around half a million observations of temperature, pressure, wind speed and direction, humidity and many other properties to provide the starting conditions of our weather forecast model.

Assimilation - accurately estimating the current weather conditions

The process of ingesting the raw observational data into a numerical representation of the atmosphere in the forecast model is known as assimilation. Since even tiny changes in the atmospheric conditions can lead to drastically different weather patterns after only a short time it is vital that the current state of the atmosphere is represented as accurately as possible. This process is highly mathematical and today it takes the supercomputer longer to accurately estimate the current atmospheric state than it does to actually make the forecast.

Creating a numerical model of the atmosphere using scientific understanding of the environment

Our research scientists are continually working to improve our understanding of atmospheric processes, so that these can be better simulated in our forecast model, the Unified Model, and ultimately, lead to more accurate forecasts. This is done through a combination of making and studying new observations (such as from our research aircraft FAAM) and advanced numerical simulations.

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.