News and Announcements - 17 August 2021:
NCL v6.6.0 and new bug fix (v2.0.3): In using NCL v6.6.2 (and
likely v6.6.0 and later) a totype warning occurs whenever one
of the outPressure variables is created. This warning appears
to be related to a new function: wrf_user_interp_level
which among other things replaces wrf_user_intrp3d. It appears
that as a part of the deprecation of wrf_user_intrp3d the
error/bug involving totype was introduced. Because of the
dichotomy with wrf_user_intrp3d with the warning issue in
v6.6.2 and wrf_user_interp_level only availabe v6.6.0 and
later, the fix is a bit of a hack in that it needs to be applied
only to v6.6.0 and later using the get_ncl_version function.
The wrfout_to_cf release v2.0.3 addresses this bug fix.
End of Life:
As is likely known by now, the development of NCL has stopped
with the release of v6.6.2. The reason for this stop to
NCL development is for the pivot at NCAR towards python.
NCL 6.6.2 is still intended to be around for a long time, and
this script/program will be as well. However, similar to NCL,
v2.0.3 is anticipated to be the last version of wrfout_to_cf.
The plans are to port wrfout_to_cf to python but it is
unknown when such a transition will occur.
The native WRFOUT files are not
the easiest NetCDF files to use.
- The variables are based on WRF development history and
not necessarily community acceptance.
- Several of the key variables (i.e. u and v wind) are on
the staggered WRF horizontal grid.
- The vertical levels are on the native eta vertical
- A large number of variables are included in the WRFOUT
files related to the WRF simulation and not the applicable
- The associated NetCDF attributes may not be helpful.
- The WRFOUT files can often be considerably larger than
required for a research project, especially when building
an archive of simulations for a study.
Modifying the Registry can change
the variables included in the WRFOUT files.
- It can be a tedious and potentially messy process to
make significant modifications to the Registry.
- Some variables are included in WRFOUT for reasons the
user may never know. Removing the variables may
create unintended consequences.
- The variables are still on the staggered grid and on the
model vertical levels.
What it is - one solution:
wrfout_to_cf is an NCL based
script designed to create CF compliant NetCDF files with user
selectable variables, time reference, vertical levels, and
spatial and temporal subsetting.
There are a number of WRF post-processing utilities to create
output files and/or graphics for scientific use (e.g. NCEP UPP,
RIP4, ARWpost, VAPOR). wrfout_to_cf is just one solution
to create post-processed WRF output files that are more
convenient to work with on a research project.
This is not the most computationally efficient post-processing
utility. This utility does not fit all applications. It is
designed to be a simple and user flexible post-processing
CF compliant (http://cf-pcmdi.llnl.gov/):
Climate and Forecast (CF) is a
metadata convention designed to promote the sharing and
utilization of similar NetCDF data files. CF conventions
have been adopted by a number of research projects and groups as
a primary standard. Some graphics programs (e.g. IDV) can
readily read CF compliant NetCDF files.
The CF convention does not standardize variable names. The
selected variable names for this post-processing script are
partially based on WRF conventions, consistency amongst the
variables, a self-describing simple approach, and standardized
The data in CF files are described by specifying standard
attributes for the variables.
The variables contain coordinate information accessed through
The time in encoded with units specified by a specified
"time_unit" since a given "reference_time.
= "hours since 2001-01-01 00:00:00"
NCL Based (http://www.ncl.ucar.edu/):
NCL is a free interpreted language
designed for scientific data processing and visualization.
NCL Is available for a variety of operating systems including
Linux, Mac OS X, and Cygwin/X running on Windows.
wrfout_to_cf heavily leverages the WRF-ARW NCL scripts and
functions that are included in the NCL libraries. These
built-in NCL functions include diagnostics and tools for
unstaggering the grids and interpolating to pressure levels.