The Network Weather Service is a distributed system that periodically monitors and dynamically forecasts the performance various network and computational resources can deliver over a given time interval. The service operates a distributed set of performance sensors (network monitors, CPU monitors, etc.) from which it gathers readings of the instantaneous conditions. It then uses numerical models to generate forecasts of what the conditions will be for a given time frame. We think of this functionality as being analogous to weather forecasting, and as such, the system inherits its name.