Unified Post Processor (UPP) | FAQ's

Starting with V3.0 UPP can output grib2 format. V3.1 contains numerous updates and bug fixes for grib2, it is suggested to upgrade to V3.1 for grib2 use.

No, UPP does not currently support netcdf4. This also means that the WRF compilation should not turn on netcdf4 option.

We are not able to support all platform and compiler combinations out there but will try to help with specific issues when able. We always welcome and are grateful for user contributed configurations.

UPPV2.1 and later versions depend on having at least WRFV3.5 (or later) already compiled. Install WRFV3.5 (or later).

This error indicates a failure in unipost.exe. The errors and output from this executable are redirected to a log file unipost_d01.000.out for each domain and forecast hour. Please look in this file for details on what the actual error/problem is.

This may be a memory issue, try increasing the number of cpu’s or spreading them out across nodes (e.g. increase ptiles).

We also know of one version of MPI (mpich v3.0.4) that does not not work with UPP. A work-around was found by modifying the UPP/src/unipost/WRFPOST.f routine to change all unit 5 references (which is standard I/O) to unit 4 instead.

We have received feedback that some parallel builds do not always increase the performance. UPP was optimized for operational use at NCEP, you may see that there is little increase in performance for serial versus parallel on your platform. We are looking into these parallel performance issues.

Yes, use the sample script in the scripts/ directory: run_unipostminutes.

While we always recommend having one output time per file, there is a sample script in the scripts/ directory to handle this type of output: run_unipost_frames.

You may see this error in your unipost_d01.00.out files. It is not actually an error and does not mean that your run has necessarily failed. It is more of a warning telling you that a particular variables, e.g. HTOP, was not found in your wrfout file. UPP reads through your wrfout file and tries to find all of the possible fields for that model, even if they are not needed in calculation for the fields you request, and displays this warning message to inform the user. As long as that particular variable is not needed in the calculation of your requested output fields in wrf_cntrl.parm, then this error is just a warning.

It is possible that the field you are trying to request is dependent on the core (ARW or NMM). Also, certain fields can be dependent on model configuration, such of physics choices. Know your data and what you are expecting from the output. We will continue to try to update the user guide as often as possible to reflect limitations, additions, and changes in output fields.

We have received two sample parm files to do this. One from the operational community and one from the user community. You may try either, we recommend trying the user provided file first. Please keep in mind that these files may need to be modified to fit your particular case.

Community contributions: Download this wrf_cntrl.parm and Vtable file and use these procedures. Use with caution as these have not been thoroughly tested and the limitations are unknown at this time.

Operational contribution: Download this wrf_cntrl.parm file and use these procedures. Use with caution as these have not been thoroughly tested and the limitations are unknown at this time.

This warning appears for some platforms/compilers because a call in the nemsio library is never used for referenced for a serial build. This is just a warning and should not hinder a successful build of unipost.exe or negatively impact your UPP run.

No, UPP cannot handle WRF output in double precision format at this time.

This error message is display when using the most recent version of the wgrib2 utility on files for forecast zero that contain accumulated or time-averaged fields. This is due to the newer versions of wgrib2 no longer allowing for n parameter to be zero or empty.

Users should consider using a separate control file (postcntrl.xml / postxconfig-NT.txt) for forecast hour zero that does not include accumulated or time-averaged fields, since they are zero anyway. Users can also continue to use an older version of wgrib2.

For re-gridding Grib2 unipost output, the wgrib2 utility can be used. Complete documentation on grid specification with examples of re-gridding for all available grid definitions can be found at:


An example of how operations uses wgrib2 to interpolate to a lat-lon grid is given in the "Examples of wgrib2" section of the UPP User's Guide for v4.1.

Still Need Help?
Refer to the Users' Guide to see if the answer is there.

New Support System:  UPP is currently transitioning from using the upp-help@ucar.edu email system for user questions to web-based user forums for interacting with users and answering questions.  Beginning October 1, 2020, users sending email questions to upp-help@ucar.edu will be directed to post their questions on the proper user forum.  There are currently two forums users may wish to post questions depending on the topic: 1) The UPP section of the WRF Users Forum, and 2) The UPP section of the UFS Users Forum.  As the names suggest, UPP questions related to processing WRF data should be posted to the WRF Forum.  Other general UPP questions and those related to UFS applications should be posted to the UFS Forum.  UPP staff will be monitoring the forums and addressing questions through these platforms.

UFS Forum:


WRF Forum:


All Questions:

  • Version of UPP and WRF
  • Platform information
  • Description of problem
    • Compiling Questions:
      • compile.log
      • configure.upp
      • Compiler version information
    • Runtime Questions:
      • run_unipost script output
      • unipost_d01.00.out file
      • List of commands executed