STFM

Tutorials

GFS Guide

How to download GFS wind forecast data directly from the source, without using the built-in Downloader.

Use the Downloader and Converter first. They fetch and prepare GFS winds automatically, with no manual file hunting. If you're not getting good results with them, you can get this data manually by following the guide below. See the Downloader Guide and Converter Guide first.

Overview

GFS (Global Forecast System) provides the atmospheric wind data STFM uses to add wind-driven drift and intensify evaporation. Historical GFS data is archived by NSF NCAR's Geoscience Data Exchange (GDEX), dataset d084001, and served as individual GRIB2 files through the Open Science Data Federation (OSDF) a plain directory listing, not a request form like HYCOM's.

This is a bare file browser: click a folder to open it, click a filename to download it immediately there's no area or variable selection, and no way to select multiple files at once. Each click downloads one file.

Finding the right files

  1. Direct link: osdf-cache-01.gwave.ics.psu.edu/.../d084001. The specific server address can vary (it may be routed through different OSDF cache nodes), but it always follows the same path structure: .../ncar/gdex/d084001/
Directory listing of /ncar/gdex/d084001 showing year folders from 2015 through 2026
The top level: one folder per year. A couple of loose sample files also sit here ignore those and go into the year folder you need.
  1. Click into the year folder matching your spill date.
Directory listing inside a year folder, showing one subfolder per date in YYYYMMDD format
Inside a year folder: one subfolder per date, named YYYYMMDD.
  1. Click into the specific date folder (YYYYMMDD) you need.
Directory listing inside a date folder, showing individual GRIB2 files named gfs.0p25.[run].f[hour].grib2
Inside a date folder: the individual forecast files, named gfs.0p25.[run].f[forecast hour].grib2.
  1. Files are named following this pattern: gfs.0p25.[YYYYMMDDHH].f[HHH].grib2
    • The [YYYYMMDDHH] part is the model run time GFS runs four times a day, at 00, 06, 12, and 18 UTC.
    • The f[HHH] part is the forecast hour offset from that run f000 is the analysis itself, f003 is 3 hours ahead, f006 is 6 hours ahead, and so on.

The listing isn't sorted by run or forecast hour files from different runs are mixed together in the same folder. Use your browser's find-on-page search (Ctrl+F / Cmd+F) and search for the run timestamp you need to locate the right files faster.

Downloading

  1. Click a filename it downloads immediately, one file per click. There's no batch selection on this server.
  2. To cover your full simulation period, repeat this for each forecast hour you need from the same run (f000, f003, f006 …) until you've spanned your simulation window.
  3. Save all files into your project's RAW_DATA/ folder, keeping the original filenames intact the Converter reads the date and forecast hour from the filename itself.

Next steps

With the GRIB2 files in RAW_DATA/, open the STFM Converter tool and select the Global Forecast System (GFS) card to convert and clip them to your project's grid. See the Converter section of the main Getting Started guide for that step.

More Guides

Already have your winds?

For a realistic simulation, grab the HYCOM currents next too.

HYCOM Guide Back to Tutorials