Weather model
Models & data numerical weather model forecast model numerical weather prediction model
A weather model calculates how the atmosphere develops using physical equations. It divides Earth and the air above it into a three-dimensional computational grid.
From measurements to a forecast
The starting analysis combines observations with existing model information. A computer then calculates changes in wind, temperature, pressure and moisture at many grid points and levels. Cloud and precipitation are among the resulting quantities.
Why every street is not represented separately
A model grid has limited resolution. Buildings, individual trees and small eddies are often smaller than its cells, so their effects are simplified. A displayed decimal place therefore does not imply that level of accuracy at your front door.
Where uncertainty comes from
- Observations contain gaps and measurement errors.
- Small starting differences can become large later.
- Some physical processes require approximations.
Several calculations give a fuller picture
Models such as ICON restart regularly with new data. Different models and ensemble members may show different developments. Those differences help reveal which details remain uncertain.
A weather model is a reasoned calculation, not a photograph of the future. Comparing it with current observations, other runs and an ensemble makes its output easier to interpret.