Global Forecast System

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An example of a forecast product from the GFS, in this case a 96-hour forecast of 850 mb geopotential height and temperature
An example of a forecast product from the GFS, in this case a 96-hour forecast of 850 mb geopotential height and temperature

The Global Forecast System (GFS) is global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up 16 days in advance, but with decreasing spatial and temporal resolution over time (it is widely accepted that beyond 7 days the forecast is little better than guesswork).

The model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour.

This is the only global model for which all output is available, for free, over the internet (as a result of U.S. law), and as such is the basis for most web based forecast services, e.g., Weather Underground, AccuWeather, The Weather Channel, MetCheck, Weatheronline, TheWeatherOutlook. and Weather.com.au

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