Why do numerical weather prediction models need accurate observations of the atmosphere?

Numerical weather prediction (NWP) models rely on accurate atmospheric observations because they function by solving physics-based equations to calculate how current weather conditions will change over time. To generate a forecast, these models require a precise "initial picture"—a set of measurements including temperature, pressure, wind, and humidity—to establish the starting state of the atmosphere.12

The forecasting process is iterative: the model calculates changes for a short interval, adds those changes to the initial conditions to create a new map, and then uses that map as the starting point for the next step. Because this process is cumulative, any inaccuracies in the initial data or small errors in the calculations can grow over time. If the starting observations are not accurate, these errors accumulate rapidly, eventually rendering the forecast unreliable. Consequently, high-quality, real-time data from sources like meteorological satellites, radar, and aircraft are essential to provide the accurate initial conditions necessary for the model to produce a valid, useful prediction.132