Global Forecast System
Encyclopedia
Numerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
computer model run by NOAA. This mathematical model
Mathematical model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
is run four times a day and produces forecasts
Weather forecasting
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location. Human beings have attempted to predict the weather informally for millennia, and formally since the nineteenth century...
up to 16 days in advance, but with decreasing spatial and temporal resolution over time. It is widely accepted that beyond 7 days the forecast is very general and not very accurate, and most nongovernmental agencies rarely use any of the model's results beyond 10 days (mainly because there is no other 16-day model with which to compare). Along with the ECMWF
European Centre for Medium-Range Weather Forecasts
The European Centre for Medium-Range Weather Forecasts is an independent intergovernmental organisation supported by 19 European Member States and 15 Co-operating States...
's Integrated Forecast System
Integrated Forecast System
The Integrated Forecast System is an operational global meteorological forecasting model. IFS is developed and maintained by the European Centre for Medium-Range Weather Forecasts based in Reading, England...
(IFS) and the Canadian Global Environmental Multiscale Model
Global Environmental Multiscale Model
The Global Environmental Multiscale Model is an integrated forecasting and data assimilation system developed in the Recherche en Prévision Numérique , Meteorological Research Branch , and the Canadian Meteorological Centre ....
(GEM), both of which run out 10 days, it is one of the three predominant synoptic scale
Synoptic scale meteorology
The synoptic scale in meteorology is a horizontal length scale of the order of 1000 kilometres or more. This corresponds to a horizontal scale typical of mid-latitude depressions...
medium-range models in general use.
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. The GFS is also used to produce model output statistics
Model output statistics
Model Output Statistics is an omnipresent statistical technique that forms the backbone of modern weather forecasting. The technique pioneered in the 1960s and early 1970s is used to post-process output from numerical weather forecast models...
, both in a short range (every 3 hours, out to 72 hours) and in an extended range (every 12 hours, out to 8 days).
In addition to the main model, the GFS is also the basis of a 20-member (22, counting the control
Scientific control
Scientific control allows for comparisons of concepts. It is a part of the scientific method. Scientific control is often used in discussion of natural experiments. For instance, during drug testing, scientists will try to control two groups to keep them as identical and normal as possible, then...
and operational members) ensemble
Ensemble forecasting
Ensemble forecasting is a numerical prediction method that is used to attempt to generate a representative sample of the possible future states of a dynamical system...
that runs concurrent with the operational GFS and is available on the same time scales. This is variously referred to as a "Global Ensemble Forecast System" (GEFS or GENS) or the "Medium Range Forecast" (MRF). Ensemble model output statistics are also available out to 8 days.
This is the only global model for which all output is available, for free in the public domain
Public domain
Works are in the public domain if the intellectual property rights have expired, if the intellectual property rights are forfeited, or if they are not covered by intellectual property rights at all...
, over the internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
(as a result of U.S. law), and as such is the basis for non-state weather companies, e.g., Weather Underground
Weather Underground (weather service)
Weather Underground is a commercial weather service that provides real-time weather information via the Internet. Weather Underground provides weather reports for most major cities across the world on its Web site, as well as local weather reports for newspapers and Web sites...
, AccuWeather
AccuWeather
AccuWeather is an American media company that provides for-profit weather forecasting services worldwide.AccuWeather was founded in 1962 by Joel N. Myers, then a Penn State graduate student working on degrees in meteorology. His first customer was a gas company in Pennsylvania. While running the...
, The Weather Channel and MeteoGroup
MeteoGroup
MeteoGroup is Europe’s largest private sector weather business with forecasting offices in ten European countries and the US, sales representatives in the Far East and Middle East, and customers worldwide....
. (The IFS only has a limited amount of its output available for free, and all of the GEM's content remains under copyright.)