A weather model is a computer program that simulates the future evolution of the atmosphere. It solves the equations of motion, thermodynamics, and moisture conservation on a three-dimensional grid, starting from the best estimate of the current state.

Global models cover the entire Earth at moderate resolution. Regional models focus on smaller areas with finer grids. Physics packages represent processes that occur at scales smaller than the grid, such as clouds and turbulence. Ensemble systems run many members to sample uncertainty.

Models are updated several times per day with new observations. Their output forms the backbone of modern forecasting. Continuous research improves resolution, physics, and data assimilation. No model is perfect; each has characteristic strengths and weaknesses that forecasters learn to recognize.

• Computer simulation of the atmosphere
• Solves physical equations forward in time
• Global and regional versions
• Foundation of modern forecasts