Weather forecasting is the application of science and technology to
predict the conditions of the atmosphere for a given location and time. People
have attempted to predict the weather informally for millennia and formally
since the 19th century.
Weather forecasts are made by collecting quantitative data about the current
state of the atmosphere, land, and ocean and using meteorology to project how
the atmosphere will change at a given place.
Once calculated manually based mainly upon changes in barometric pressure,
current weather conditions, and sky conditions or cloud cover, weather
forecasting now relies on computer-based models that take many atmospheric
factors into account.