Definition
A computer-based weather prediction model run by the U.S. National Weather Service that produces forecasts of atmospheric conditions worldwide. It uses observations from satellites, weather balloons, aircraft, and surface stations as inputs, then applies physics-based equations to predict temperature, wind, pressure, humidity, and precipitation out to about 16 days ahead. Forecast products are issued four times daily and form the backbone of many aviation weather products pilots rely on.
Plain English
A worldwide weather forecasting computer model that predicts what the atmosphere will do over the next two weeks. Many of the weather products pilots use are built from its output.
Context Anchor
Seen in aviation weather discussions, forecast tools, and weather briefings that use model-based forecast data.
Why Pilots Care
Supplies the wind, temperature, and weather data that pilots use to select altitudes, calculate fuel, and anticipate turbulence or icing.
Analogy
Think of it like a very large weather calculator. It takes the weather information available now and works forward to estimate what conditions may be later.
Intuition Check
Do not read Global Forecast System as a finished pilot weather briefing. It is a forecast model that helps create weather guidance and products.
Example Sentence 1
The winds-aloft forecast for tomorrow's cross-country was generated from the latest Global Forecast System run.
Example Sentence 2
Changes in the Global Forecast System output prompted an earlier departure to avoid an approaching line of thunderstorms.