Numerical weather prediction
Numerical weather prediction is the way weather forecasts are made.  This is done using computer models of the atmosphere. Such models describe the current weather conditions, and how they change over time using equations. Using the current weather conditions, the equations can be solved, or approximated to tell what the weather will be like in the near future. The relevant physical parameters, such as pressure, temperature, the direction and the speed of the wind are taken to be functions of time. These are modelled with a system of partial differential equations. This is a dynamic system that is solved numerically. Most of these equations are implemented using FORTRAN. The equations are approximated. Since the number of calculations is huge, supercomputers usually do them, to finish before it's too late.