NCEP navgem file missing records

[joleenf]

Hi,

I am trying to read data from a navgem grib2 file hosted by ncep:
https://nomads.ncep.noaa.gov/pub/data/nccf/com/fnmoc/prod/
Specifically,
https://nomads.ncep.noaa.gov/pub/data/nccf/com/fnmoc/prod/navgem.20220826/navgem_2022083000f006.grib2

When the following lines are run:

import xarray as xr
isobaric_data = xr.open_dataset('navgem_2022083012f003.grib2', engine="cfgrib",
                                backend_kwargs={'filter_by_keys': {'typeOfLevel': 'isobaricInhPa'}})

Some of the expected data is loaded:
isobaric_data.data_vars returns:

Data variables:
t (isobaricInhPa, latitude, longitude) float32 ...
gh (isobaricInhPa, latitude, longitude) float32 ...
u (isobaricInhPa, latitude, longitude) float32 ...
v (isobaricInhPa, latitude, longitude) float32 ...

But, the file contains data such as relative humidity on isobaric levels as well (output from wgrib2):

34:6002652:d=2022083012:RH:300 mb:3 hour fcst:
38:6867216:d=2022083012:RH:350 mb:3 hour fcst:
41:7428414:d=2022083012:RH:400 mb:3 hour fcst:
45:8301392:d=2022083012:RH:450 mb:3 hour fcst:
49:8975749:d=2022083012:RH:500 mb:3 hour fcst:
53:9842749:d=2022083012:RH:550 mb:3 hour fcst:
54:10104756:d=2022083012:RH:600 mb:3 hour fcst:
55:10368921:d=2022083012:RH:650 mb:3 hour fcst:
58:10850969:d=2022083012:RH:700 mb:3 hour fcst:
62:11876468:d=2022083012:RH:750 mb:3 hour fcst:
63:12210334:d=2022083012:RH:800 mb:3 hour fcst:
66:12785128:d=2022083012:RH:850 mb:3 hour fcst:
70:13733245:d=2022083012:RH:900 mb:3 hour fcst:
76:15051420:d=2022083012:RH:950 mb:3 hour fcst:
79:15657530:d=2022083012:RH:1000 mb:3 hour fcst:

Though this data is not on the same isobaric levels as data such as the t, u, v, gh which cfgrib does load (only VGRD shown here):

11:2136311:d=2022083012:VGRD:70 mb:3 hour fcst:
15:2710454:d=2022083012:VGRD:100 mb:3 hour fcst:
20:3598444:d=2022083012:VGRD:150 mb:3 hour fcst:
25:4423347:d=2022083012:VGRD:200 mb:3 hour fcst:
30:5285880:d=2022083012:VGRD:250 mb:3 hour fcst:
36:6429146:d=2022083012:VGRD:300 mb:3 hour fcst:
43:7854079:d=2022083012:VGRD:400 mb:3 hour fcst:
51:9395574:d=2022083012:VGRD:500 mb:3 hour fcst:
60:11342525:d=2022083012:VGRD:700 mb:3 hour fcst:
68:13290902:d=2022083012:VGRD:850 mb:3 hour fcst:
74:14554430:d=2022083012:VGRD:925 mb:3 hour fcst:
81:16344765:d=2022083012:VGRD:1000 mb:3 hour fcst:

Is there any way to access the RH data using cfgrib?
Thanks - Joleen

[iainrussell]

Hi @joleenf,

Indeed, the problem is that r is not on the same levels as the other parameters, and so they do not form a consistent hypercube. However, you can still load 'r' by itself into a separate dataset:

rh = xr.open_dataset('navgem_2022083012f003.grib2', engine="cfgrib",
                                backend_kwargs={'filter_by_keys': {'shortName': 'r'}})

and then you can see if there's anything you can do in xarray to merge that into your other dataset.

Best regards,
Iain

[joleenf]

Excellent! Thanks.