GFS

This article is about GFS and is under construction

Global Forecasting System (GFS) files are packed under the GRIB protocol. There are two different types of GRIB files GRIB1 and GRIB2 files. They differ in the way and the software used to convert them into HDF5 mohid input files and normally the former can be found on the reanalysis solutions while the latter is the format used for forecast.

Reanalysis data in GRIB1 format can be collected from the NCEP FNL Operational Model Global Tropospheric Analyses, continuing from July 1999 found on this web address. To collect the data you must become a registered user http://dss.ucar.edu/datasets/ds083.2/

Forecasting data in GRIB2 format it is collected from the NOAA ftp site ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/ within this page it is located different folders, that are changing continuosly the name of the folder indicate the date and time when they were produced with the following format gfs.yyyymmddhh . In example, the folder named gfs.2009081406 indicated results produced at 6 a.m. of the 14th of August 2009. Inside each folder, It can be found different files, our interest are mainly in the files named with the following format gfs.tXXz.pgrb2bfYY that indicate that are gfs files, produced at the time XX and that correspond to the YY hour after the beginning of the simulation. Results are produced every 3 hours and the size of each file is around 40 MB.

Windows

GRIB1 files are first unpacked into ASCII or binary files with the help of WGRIB while GRIB2 are converted into ASCII, binary or NETCDF. Once our files are converted into ASCII text files they would be converted into HDF5 files through a Matlab code.

The WGRIB and WGRIB2 programs can be downloaded at the NOAA´s Climate Prediction Center website http://www.cpc.noaa.gov/products/wesley/

WGRIB2

The WRIB2.exe is executed through a Dos command-line and present a wide list of options. In order to reduce the computing space, the extracted domain has been limited through the option -small_grib. A typical command-line using this option would be:

wgrib2 20090101/gfs.t00z.pgrb2f00 -small_grib -10:11 30:45 Smallergrib00.grib

where -10:11 is the longitude interval, 30:45 is the latitude interval and Smallergrib00.grib correspond to the new grib file.

Once executed, the outputs are .dat files each containing a different property with the following correspondences:

 HR2m - Relative Humidity 2 m above ground [%].
 LAND - Land Cover (1=land, 0=sea) [Proportion]. 
 MSLP - Pressure Reduced to Mean Sea Level [Pa].
 TCDC - Total Cloud Cover [%].
 TMP2m - Temperature 2 m above ground [K].
 U - U-Component of Wind 10 m above ground [m/s].
 V - V-Component of Wind 10 m above ground [m/s].