weermodel

A weermodel, or weather model, is a numerical model used to forecast atmospheric conditions by solving the equations of atmospheric dynamics and thermodynamics on a computational grid. It uses current observations to initialize the state of the atmosphere and then integrates the equations forward in time to produce forecast fields such as temperature, wind, humidity, precipitation, and pressure.

The atmosphere is represented on a three-dimensional grid or set of grid points. Global models cover the entire planet but typically have coarser resolution, while regional models focus on a smaller area and can use higher resolution. Physical parameterizations approximate subgrid-scale processes such as cloud formation, precipitation, radiation, and turbulence. Because small errors in the initial state grow over time, modern forecasting relies on data assimilation to combine observations with model forecasts and on ensemble methods that run many forecasts with slightly different initial conditions or model configurations to estimate uncertainty.

Common examples of weermodels include global models such as ECMWF’s Integrated Forecast System (IFS), NOAA’s Global Forecast System (GFS), the UK Met Office model, and Japan’s JMA model; regional models include COSMO and the Weather Research and Forecasting model (WRF). Outputs are provided as gridded fields and are used by meteorologists and weather services to produce routine forecasts and severe-weather warnings.

Limitations include finite resolution and imperfect physics, which produce forecast error and uncertainty, particularly beyond several days and in data-sparse regions. Ongoing development aims to improve cloud and convection representations, data assimilation, ensemble calibration, and the integration of new observations and physics to enhance forecast skill.