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Global Data Assimilation System (GDAS)

A plot of GDAS output showing the amount of water in snow covering the ground on February 1st, 2012 at 00UTC. This image was produced by visualizing GDAS output data with NASA’s Panoply visualization tool.

The Global Data Assimilation System (GDAS) is the system used by the National Center for Environmental Prediction (NCEP) Global Forecast System (GFS) model to place observations into a gridded model space for the purpose of starting, or initializing, weather forecasts with observed data. GDAS adds the following types of observations to a gridded, 3-D, model space: surface observations, balloon data, wind profiler data, aircraft reports, buoy observations, radar observations, and satellite observations.

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GDAS data are available through NCEI's NOAA National Operational Model Archive and Distribution System (NOMADS) as both input observations to GDAS and gridded output fields from GDAS. Gridded GDAS output data can be used to start the GFS model. Due to the diverse nature of the assimilated data types, input data are available in a variety of data formats, primarily Binary Universal Form for the Representation of meteorological data (BUFR) and Institute of Electrical and Electronics Engineers (IEEE) binary. The GDAS output is World Meteorological Organization (WMO) Gridded Binary (GRIB).

Product Types

Product	Grid/Scale	Period of Record	Model Cycle	Output Timestep	Data Access Links
GDAS Snow, Ice, SST, Satellite, Ship, Aircraft (GRIB and BUFR)	1° by 1°, 0.5° by 0.5°, 0.25° by 0.25°	05Jun2020–Present (approx. one year to present online)	4/day: 00, 06, 12, 18UTC	Anl, +00, +03, +06, +09 hours	HTTPS
GDAS Snow, Ice, SST, Satellite, Ship, Aircraft (GRIB and BUFR), Historical	1° by 1°, 0.5° by 0.5°, 0.25° by 0.25°	21Apr2019–11May2020	4/day: 00, 06, 12, 18UTC	Anl, +00, +03, +06, +09 hours	HTTPS
GDAS - Daily Tar Files	1° by 1°	01Jan2001–21Feb2012	4/day: 00, 06, 12, 18UTC	Anl, +00, +03, +06, +09 hours	HAS
GDAS - Hourly Tar Files	1° by 1°, 0.5° by 0.5°, 0.25° by 0.25°	13Feb2012–Present	4/day: 00, 06, 12, 18UTC	4/day: 00, 06, 12, 18UTC	HAS
GDAS - Daily BUFR Files	1° by 1°, 0.5° by 0.5°, 0.25° by 0.25°	13Feb2012–Present	4/day: 00, 06, 12, 18UTC	Anl, +00, +03, +06, +09 hours	HAS