Final answer:
A supercomputer is used for weather forecasting on a national or worldwide scale due to its ability to perform complex calculations required for accurate predictions.
Step-by-step explanation:
For weather forecasting on a national or worldwide scale, the type of computer typically used is a supercomputer. Supercomputers have the computational power necessary to perform the billions of complex calculations required for predicting weather patterns. Such forecasts are crucial for many aspects of life and economy, including agriculture, where they influence decisions such as when to plant and harvest crops.
Organizations like NASA and the National Oceanic and Atmospheric Administration (NOAA) rely on supercomputers to process large weather data sets and provide accurate weather forecasts that the public, including farmers, can access to make informed decisions. The role of supercomputers in weather prediction exemplifies how technology has evolved and significantly changed our access to and use of information.