Home > CMC Global Ensemble Data documentation
Revisions:
- Dec 04, 2013 - CMC implements Global Ensemble Prediction System (GEPS) 3.1.0 - Click here for details
- Feb 13, 2013 - CMC implements Global Ensemble Prediction System (GEPS) 3.0.0 - Click here for details
- May 15 2012 - Added 3.2.6 - Correction to CMC GRIB2 encoding of its Freezing Rain and Ice Pellets

The Canadian Meteorological Center (CMC) ensemble dataset is the output from the Canadian Global Ensemble Prediction Sytem (GEPS) which consists of 1 control and 20 perturbed members. The CMC ensemble data is available daily for the 00Z and 12Z cycle for all ensemble members. This dataset originates from CMC and NCEP repackages the original data provided into in a format similar to that of NWS/NCEP's Global Ensemble Forecast System and Fleet Numerical Meteorology and Ocenography Center (FNMOC)'s Global Ensemble Forecast System. The disclaimer below outlines some of the differences between the original CMC ensemble grib2 dataset and NCEP's repackaged version of that dataset. The disclaimer also provides more information on the Canadian GEPS system and products as well as how to contact Environment Canada if more information on their original dataset is required.


Users of the Canadian Global Ensemble Prediction System (GEPS) data retrieved from this NCEP NOMADS server should be aware of the following information concerning this dataset.

1.0 Environment Canada (EC) is the provider of the original data which comes from its Global Ensemble Prediction System (GEPS). EC grants a free license to use its data to any user, as long as Environment Canada is credited as the source of the Canadian data in any downstream products or distribution. The data was originally produced at the Canadian Meteorological Center (CMC) offices of Environment Canada.

2.0 The Canadian GEPS system runs twice daily at CMC. Both the 00UTC and 12UTC runs produce forecasts with lead times extending from 000 hours to 384 hours. The CMC GEPS system is defined as a multi-model ensemble system which includes an unperturbed control (referred to as control member 0) along with 20 perturbed members. A description of each of the members is available at: this EC page by clicking here.

3.0 The Canadian GEPS GRIB2 data files retrieved from the NOMADS server are not the original GRIB2 files that were provided by CMC but instead are GRIB2 files of CMC GEPS data that have been re-packaged by NCEP. The meta information in the NOMADS version of the CMC GEPS data can be quite different in some areas than the meta information in the original GRIB2 files provided by CMC.

3.1 The following links can provide users with details of GRIB2 meta information from the original CMC GEPS GRIB2 data encoded at the source by CMC for the NAEFS project.

CMC GEPS Control member, lead time = 000, click here to access grib2 meta information from the original CMC GRIB2 dataset.

CMC GEPS Control member, lead time other than 000, click here to access grib2 meta information from the original CMC GRIB2 dataset.

CMC GEPS Perturbed member, lead time = 000, click here to access grib2 meta information from the original CMC GRIB2 dataset.

CMC GEPS Perturbed member, lead time other than 000, Click here to access grib2 meta information from the original CMC GRIB2 dataset.

3.2 Some of the differences between the original CMC GRIB2 files and the equivalent NOMADS dataset are:

3.2.1 NCEP has combined U and V wind parameters into one GRIB2 message instead of separate messages as per the original CMC GEPS GRIB2 files

3.2.2 NCEP has modified CMC's original four cummulative precipitation type parameters (rain, snow, freezing rain and ice pellets) to instead offer CMC precipitation type information as categorical precipitation by type for each 6 hour interval.

3.2.3 NCEP has modified CMC's original seven flux parameters (lhtfl, shtfl, dswrf, dlwrf, uswrf, ulwrf, ulwrf-olr) from cummulative amounts in the original CMC GRIB2 to average flux values for each 6 hour interval in the NOMADS grib2 files.

3.2.4 Even though NCEP presents CMC GEPS meta information in the NOMADS grib2 files as member data being [positively,negatively] perturbed, the CMC ensemble system is a multi model ensemble where members are perturbed randomly.

3.2.5 Users are strongly advised to use the information at the links in 3.1 above to get information on how CMC's GEPS GRIB2 dataset was originally encoded at the source. It is hoped that eventually, the meta information contained in the NOMADS GRIB2 version of the CMC GEPS data will correspond to the meta information from the original CMC GEPS GRIB2 files.

3.2.6 Correction CMC GRIB2 encoding of Freezing rain and Ice pellets: Starting with its May 15, 2012 12Z data, CMC encodes Freezing Rain using parameter number = 67 (prior to this date it was incorrectly encoded as #68). CMC now encodes Ice Pellets using Parameter Number = 68 (prior to this date is was incorrectly encoded as #67). This parameter number is defined in table 4.2.0.1.

4.0 There are also, on the NOMADS server, additional datasets related to the EC GEPS GRIB2 data that are also generated by and then made available by NCEP. These derived datasets were not originally provided by EC. For exemple files of the type cmc_geavg.t12Z_pgrb2af[00,06,12..] are files which contain data calculated by NCEP from CMC GEPS data.

5.0 Users wishing to access CMC GEPS data in its original GRIB2 configuration as was provided by EC can do so by using the information provided at this link. Note that this link provides access to CMC's NAEFS GEPS raw prog variables only. GRIB2 files at this link have also been bundled to contain (1 variable/all members/timestep) while the original CMC GRIB2 dataset provided to NCEP was bundled as (all variables/timestep/per member).

6.0 Information on NAEFS products produced by EC from its original datasets is available by clicking on this link

7.0 Users who wish to use Canadian GEPS data for activities other than data visualization should be aware of the differences between the original CMC GEPS GRIB2 dataset and the NOMADS version of the CMC GRIB2 data.


For questions on the NOMADS version of the CMC dataset, pleast contact the NOMADS Help Desk


For additional questions on the original CMC GRIB2 ensemble dataset, please contact Environment Canada