NAEFS data in GRIB2 format

This page describes the North American Ensemble Forecast System (NAEFS) data available in GRIB2 format on the Canadian Meteorological Centre (CMC) HTTP data server.


The data is available using the HTTP protocol and resides in a directory that is plainly accessible to a web browser. Visiting that directory with an interactive browser will yield a raw listing of links, each link being a downloadable GRIB2 file. In practice, we recommend writing your own script to automate the downloading of the desired data (using wget or equivalent). If you are unsure of how to proceed, you might like to take a look at our brief wget usage guide.

The data can be accessed at the following URLs:


File name nomenclature

The file names have the following nomenclature:


  • CMC_naefs-geps-raw: constant string indicating that the data is from the Canadian Meteorological Centre (CMC), the dataset (naefs), the model used (geps: Global Ensemble Prediction System) and the data type (raw).
  • latlon1p0x1p0: constant string indicating the data resolution.
  • Variable: Variable type included in this file. To consult a complete list, refer to the variables section.
  • LevelType: Level type. To consult a complete list, refer to the variables section.
  • Level: Level value. To consult a complete list, refer to the variables section.
  • YYYYMMDD: Year, month and day of the beginning of the forecast.
  • HH: UTC run time [00,12]
  • Phhh: P is a constant character. hhh is the forecast hour [000,006,012,..,378,384]
  • allmbrs: constant string indicating that all the members of the ensemble are inluded in this file
  • grib2: constant string indicating the GRIB2 format is used

Example of file name:

This file originates from the Canadian Meteorological Center (CMC) and contains the raw (raw) data of the Global Ensemble Prognostic System data for the North American Ensemble Forecast System (naefs-geps). The data in the file start on September 1st 2010 at 00Z (2010090100). It contains the U-component wind (UGRD) at the isobaric level 925 mb (ISBL_0925) for the forecast hour 78 (P078), for all members (allmbrs) in GRIB2 format (.grib2).


The models forming the ensembles run at the source on an uniform grid at 0.5 degree. The fields included in the series of GRIB2 data are available on the NAEFS latitude-longitude grid of 360 x 181 points, covering the Earth surface at a resolution of 1.0 x 1.0 degree, which corresponds roughly to 100 km between grid points.

This table lists details of the latitude-longitude grid used in the encoding of the GRIB variables.
Grid Parameter Value of Parameter
ni 360 points
nj 181 points
resolution 1 degree
first grid point coordinate 90° S
000° E

Models and variables description

Links in the first column below (Ensemble models (members)), provide details on each of the models in the CMC ensemble system.

Links in the second column below (Forecast hour), provide information on which variables are included in each of the CMC NAEFS GRIB2 files, along with detailed information on sections 0-6 for each of the records in these GRIB2 files.

For all models, the number of variables (or records) in the 0-hour forecast files is less than the number of variables (or records) in the non-zero forecast hours because some variables are not produced at forecast hour = 0.

This table offers links to information describing ensemble members and links to information on the available variables
Ensemble models (members) Forecast hour
Control model (member 0) 0-hour forecast
Non-zero forecast hours
Perturbed models or members 0-hour forecast
Non-zero forecast hours

What we are doing

Date modified: