You are here

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.


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).

Offline data ordering of Global Data Assimilation System (GDAS) with the HDSS Access System (HAS) requires checking the "Bulk Request" option. While this is not enforced by the site, requests submitted without the bulk option are not supported and will not return data. Bulk datasets requests are large and cannot be subsetted, so start with small requests (one day of data) to ensure you find it usable.

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) 0.5º by 0.5º 14Jan2015 - Present 4/day: 00, 06, 12, 18UTC Anl, +00, +03, +06, +09 hours FTP HTTP HAS
GDAS ​Snow, Ice, SST, Satellite, Ship, Aircraft (GRIB and BUFR) 1º by 1º 01Jan2001 - 14Jan2015 4/day: 00, 06, 12, 18UTC Anl, +00, +03, +06, +09 hours FTP HTTP HAS

Data Usage Notes


Publication References


Miscellaneous Documentation

NCEP: GFS/GDAS Changes Since 1991

NCEP Global Model and Cycling Analysis Rerun and Retrospective Data, November 2001

NCEP Environmental Modeling Center (EMC) Mesoscale Modeling Branch Publication Listing