NCL Graphics: Plotting WRF-ARW data using NCL

This page describes how to use NCL to read and plot data and diagnostics calculated from WRF-ARW files.

To read WRF ARW data and/or calculate certain diagnostics, you need two functions:

1. addfile - this function opens a WRF-ARW NetCDF file so you can read data or calculate diagnostics. If you have more than one WRF-ARW file, use addfiles.

2. wrf_user_getvar - given the file(s) you opened in the first step, this function allows you to specify what diagnostic you want to calculate or what variable you want to read.

Once you have read a variable or calculated a diagnostic, there are two different sets of routines you can use for plotting WRF-ARW data:

1. WRF-specific plotting functions

   The folks who help develop the WRF model have created their own tutorial for plotting data using the the WRF-specific plotting functions. See the the WRF ARW OnLine Tutorial web page.

2. gsn_csm plotting functions

   The example pages linked to from this page mainly show how to plot data using gsn_csm functions, although in some cases the WRF-specific routines are also used for comparison purposes. As an example, see the "wrf_gsn_1.ncl" and "wrf_nogsn_1.ncl" scripts on the WRF gsn_csm examples page.

There are other packages developed at NCAR for analyzing and visualizing WRF-ARW data:

• wrf-python - A Python package that extends the functionality of wrf_user_getvar.

• WRF-VAPOR - An interactive tool for creating 3D visualizations of WRF data.

Mark Seefeldt [U. Colorado: Cooperative Institute for Research in Environmental Sciences (CIRES)] has created an NCL based script, wrfout_to_cf that creates new Climate-and-Forecast (CF) based NetCDF files from native wrfout NetCDF files. The script is well-documented and is easy to configure and run.

WRF-ARW netCDF files are different from netCDF files produced by the component models of the Community Earth System Model (CESM).

For example, the CESM grids do not change with time, while the WRF model(s) allow for this possibility by making the latitude and longitude arrays a function of time. NCL can readily read and process WRF netCDF files. However, some software processing tools may require data files to be Climate and Forecast (CF) convention conformant.

WRF-related questions should be addressed on the WRF Support Form.

NCL-related questions should be sent to ncl-talk.

Note about WRF-NMM data: WRF-NMM can be plotted with NCL after you used the WPP code to convert to grib format. The wrf_xxx computational functions in theory can be used for any model - although they have not been tested. The problem is that all the wrf_xxx plotting scripts have been written exclusively for WRF-ARW, and that is because the scripts handle the projection change from C to A, and also the map information. Since WRF-NMM is on a rotated E grid, the map information is very complicated to deal with.