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The numerical weather prediction (NWP) process involves assimilation of observations to provide the starting conditions for a numerical weather forecast model. The model is essentially a computer simulation of the processes in the Earth's atmosphere, land surface and oceans which affect the weather. Once current weather conditions are known, the changes in the weather are predicted by the model.
The model starts from a snapshot of the current atmospheric conditions in the area of interest — from the surface to the upper atmosphere — at points on a three-dimensional grid. The wind speed, temperature, pressure, moisture and cloud in each grid box are then stored in a computer. A set of equations, which describe all of the relevant atmospheric processes, are solved for each grid box to predict the values at that point several minutes later.
This process is repeated many times, producing a forecast, whether that is a weather forecast for the next few days or a climate prediction of the coming 100 years.
The flagship numerical model developed and used at the Met Office is called the Unified Model (UM), as, unlike most other NWP centres, different configurations of the same model are used for both weather and climate prediction.Find out more about the Unified Model
Producing even a short-range numerical weather forecast requires billions of calculations. This is a time-consuming process, therefore powerful supercomputers are needed in order to produce forecasts in a time period that is useful.Find out more about the operational NWP system
During World War I, mathematician Lewis Fry Richardson made the first numerical weather prediction. It took him months to produce a six-hour forecast — and it was wrong.
The first successful numerical weather forecast was made by a team of scientists at Princeton University, led by Jules Charney, in 1950.
The Met Office has been using the numerical weather prediction technique operationally since 1965.