GFS Reforecast V2 Grib File Downloader

This is a small package to download version 2 reforecasts from the global forecast system (GFS). The data can be accessed via the NOAA CDC data server (National Oceanographic and Atmospheric Agency). The package provides a handy way to access and download a specific subset across all reforecasts.

The GFSV2 python package provides a set of functions and two executables called GFSV2_get and GFSV2_bulk for convenient data processing.

Some more details about the most recent changes can be found in the CHANGELOG.md file.

Update (I blamed my script but it was the the HDD)

For those who came across this package in September 2017: I've written a warning that there are some unknown problems. Everyhing looks fine! The problem was caused by the hard drive where my scripts were running. Due to serious segfaults the downloader crashed relatively randomly arrr.

While (trying to) bucktrack this issue I've added some additional settings in the curl section in the config files (optional), see lisa.conf or config/default.conf files, section curl. Furthermore, an overall sleep time (see section [main] sleeptime has been added (optional). These options should help to avoid getting blacklisted if several dozens of requests are made. However, as the rules are unknown (ftp.cdc.noaa.gov) you might see what works for you (depending on internet speed, number of requests, ...).

• [curl] curllog: string, logfile. If given, pycurl drops some download logs there.
• [curl] timeout: integer. Custom pycurl timeout.
• [curl] retries: integer. 0 (only one shot), else number of retries if download fails.
• [curl] sleeptime: time in seconds to sleep if download failed (before try to download again, only has an effect if retries > 0).
• [main] sleeptime: time in seconds to sleep after each download (each file which has to be downloaded; not the time to wait between two retries).

Installation

The github repository contains the small python package which should be ready for installation. You can simply install the package by calling:

• pip install git+https://github.com/retostauffer/PyGFSV2.git

The setup.py script should automatically take care of the dependencies except wgrib2 which is used for subsetting (if configuration files with subset settings are used in GFSV2_bulk; see below). After installation you can try the installation (no subsetting) by calling:

• GFSV2_get --step 12 24 --level 700 850 --param tmp_pres --date 2005-01-01

Requirements

Requires the following python packages:

• pycurl (and standard libs like datetime, ConfigParser, argparse,logging)
• If subsetting is used (see GFSV2_bulk) the wgrib2 executable has to be callable (see CPC wgrib2 readme).

GFSV2_get executable:

The GFSV2_get executable can be used to download specific manually defined subsets of the reforecast. This can be handy during the development/specification process. However, if you would like to download larger amounts of data please have a look at the GFSV2_bulk description below!

Basic usage (shows usage help):

• GFSV2_get or GFSV2_get -h

There are two required input arguments to GFSV2_get. One is the -p/--param input, the other one is the -d/--date input. Both can contain one or more values. --param specifies which parameters or variables you would like to download, --date the dates of the model initialization. A list/description of all available parameters can be found here. The --date arguments have to be of type YYYY-mm-dd. As an example let's download tmax_2m for January 1 2014:

• GFSV2_get --param tmax_2m --date 2014-01-01
• GFSV2_get -p tmax_2m -d 2014-01-01

In addition, a -s/--steps argument can be given. The steps are the forecast lead times (e.g., 24 for the forecast 24 hours after initialization). Several steps can be defined:

• GFSV2_get -p tmax_2m -d 2014-02-01 -s 24 48

By default only mean and sprd files (ensemble mean and ensemble spread) will be downloaded. If the individual members and the control run are required (10+1) the -m/--members flag has to be set:

• GFSV2_get -p tmax_2m -d 2014-02-05 -s 24 -m

Downloading two different parameters for two different dates, only +24h forecast:

• ``GFSV2_get -p tmax_2m cape_sfc -d 2014-02-01 2014-02-02 -s 24

For pressure level variables (e.g, ugrd_pres, vgrd_pres, tmp_pres, hgt_pres and spfh_pres (see here, Table 1) the level can be given in advance to download specific levels only. Level specification in millibars or hecto pascal. An example:

• GFSV2_get -p tmp_pres -l 500 -d 2014-03-10

NOTE: The download will be skipped if the output grib file already exists! This can be crucial if you download a data set, re-specify the settings and try to run the script again. As the file already exists (even if containing different subset of data) the data won't be downloaded again. In this case simply delete the local grib files in data/YYYY/mm and re-run the job.

GFSV2_bulk executable

This is the bulk download version of the GFSV2_get executable explained above. Rather than providing a set of input arguments only one argument is allowed and required: -c/--config. -c/--config is the path to a config file. All specifications can be set in this config file. The config file allows to specify:

• Specific ouptut path/file name.
• Date range for which data should be downloaded (from to).
• Additional only flag (download data for date range if and only if the date is in month only) .
• The steps to download.
• A spatial subset (required wgrib2 installed). Data will be subsetted after downloading with respect to the specification (lonmin, lonmax, latmin and latmax).
• Parameters which have to be downloaded (each one can have it's own level/members specification).

The default config file (used by GFSV2_get) can be found here and can be used as a template to specify the data set you need. A second template config can be found in the repository called lisa.conf. After you have made a copy and changed the config specification simply call:

• GFSV2_bulk --config your_config_file.conf