[pyngl-talk] reading wrf output without lat lon variables

Huseyin Ozdemir huseyin at envs.au.dk
Sun Nov 4 17:07:08 MST 2018

Hi Bill,

Thanks a lot for your answer. I tried the first one and it gave an error because of the lack of xlat variable, then tried the second routine with giving the parameters, and it is working now.

I am now wondering if i will be able to plot my wrf outputs with wrf-python, because I noticed that getvar routine doesn’t work due to missing lat-lon variables, do you have any advice for this?

All the best,


Bill Ladwig <ladwig at ucar.edu<mailto:ladwig at ucar.edu>> şunları yazdı (29 Eki 2018 17:40):

Hi Huseyin,

Without that information in the files, you're going to have to calculate the latitude and longitude values. Since you're using Python, you can use wrf-python which contains a xy_to_ll routine that converts grid points to latitude and longitude points, as long as you're using one of the standard WRF projections, which it looks like you are (https://wrf-python.readthedocs.io/en/latest/user_api/generated/wrf.xy_to_ll.html#wrf.xy_to_ll)

Note that this will only work if you have the map projection global parameters still in your file. If not, there is an xy_to_ll_proj version where you can specify the parameters yourself. (https://wrf-python.readthedocs.io/en/latest/user_api/generated/wrf.ll_to_xy_proj.html#wrf.ll_to_xy_proj).

Hope this helps,


On Mon, Oct 29, 2018 at 7:17 AM Huseyin Ozdemir via pyngl-talk <pyngl-talk at ucar.edu<mailto:pyngl-talk at ucar.edu>> wrote:
Hi everyone,

I have a problem with reading wrf output file (Projection is Polar Stereographic); i want to compare wrf model output with observations at specific latitude-longitude coordinates, but output netcdf file has no latitude and longitude variables.

I am using my python environment for reading this netcdf file, where PyNGL and PyNIO are already installed. As an example, temp variable in this output has attributes below:

short T2 [ Time|1, south_north|150, west_east|150 ]
      FieldType : 104
      MemoryOrder : XY
      description : TEMP at 2 M
      units : K
      stagger :
      coordinates : XLONG XLAT XTIME
      add_offset : 273.8086
      scale_factor : -0.0005068767

Here, T2 variable has “Time", “south_north" and “west_east” dimensions and “south_north" and "west _east" dimensions have both 150 grids.  There is no XLAT and XLONG variables in the netcdf output, so how can i get the temperatures at any lat-lon points with just grid numbers?

Thanks in advance,


pyngl-talk mailing list
List instructions, subscriber options, unsubscribe:

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.ucar.edu/pipermail/pyngl-talk/attachments/20181105/2915497a/attachment.html>

More information about the pyngl-talk mailing list