[python-users] metpy.parse_cf doesn't set metpy_crs w/ nomads grib2 hrrr ?

• To: python-users@xxxxxxxxxxxxxxxx
• Subject: [python-users] metpy.parse_cf doesn't set metpy_crs w/ nomads grib2 hrrr ?
• From: Ken Harris <kjh@xxxxxxxxxxx>
• Date: Tue, 30 Aug 2022 00:07:13 -0700

People :

I'm trying to plot HRRR data from a nomads grib2 file, but
metpy.parse_cf doesn't set metpy_crs .  There seems to be enough
attributes (eg : GRIB_gridType, etc).  Attached is some python code
that fetches a grib2 file from nomads (and writes it into the local
directory) , then reads (w/ xarray w/ cfgrib) then metpy.parse_cf,
then prints metpy_crs.  It's works OK w/ GFS ( Projection:
latitude_longitude ), but the HRRR files gives an error : KeyError:
'metpy_crs'

Do I have to call assign_crs / assign_latitude_longitude or should
parse_cf do this ?

Thanks,
Ken

nomadsmodels = {
    'gfs_1p00' : {
        'dir' : 'gfs.{t0:%Y%m%d/%H}/atmos',
        'file' : 'gfs.t{t0:%H}z.pgrb2.1p00.f{ff1:03d}',
        'var0' : 'var_PRMSL=on',
        'var1' : 'prmsl',
    },
    'hrrr_2d' : { # conus wrfsfc
        'dir' : 'hrrr.{t0:%Y%m%d}/conus',
        'file' : 'hrrr.t{t0:%H}z.wrfsfcf{ff1:02d}.grib2',
        'var0' : 'var_MSLMA=on',
        'var1' : 'mslma',
    },
    'hrrrak_2d' : { # alaska wrfsfc
        'dir' : 'hrrr.{t0:%Y%m%d}/alaska',
        'file' : 'hrrr.t{t0:%H}z.wrfsfcf{ff1:02d}.ak.grib2',
        'var0' : 'var_MSLMA=on',
        'var1' : 'mslma',
    },
}

import datetime
import os
import xarray
import metpy

def nomads(filt0):
    model0 = nomadsmodels[filt0]

    u0 = f'https://nomads.ncep.noaa.gov/cgi-bin/filter_{filt0}.pl'
    u0 += '?dir=/' + model0['dir']
    u0 += '&file=' + model0['file']
    u0 += '&' + model0['var0']

    t1 = datetime.datetime.utcnow()
    t1 = t1.replace(hour = 0) # hack to make GFS work
    t1 -= datetime.timedelta(days = 1)

    u1 = u0.format(t0 = t1, ff1 = 0)

    fn0 = filt0 + '-parse_cf.grib2'

    c0 = f"wget -O {fn0} '{u1}'" # get grib file and write to fn0
    print(f'======= c0 : {c0}')

    os.system(c0)

    xds0 = xarray.open_dataset(fn0 , engine='cfgrib')

    #print(xds0)

    xda0 = xds0.metpy.parse_cf(model0['var1'])

    print(' # GRIB_gridType : ', xda0.GRIB_gridType)
    print(' # metpy_crs : ', xda0['metpy_crs'].item()) # HRRR : KeyError: 
'metpy_crs'

nomads('gfs_1p00')
nomads('hrrr_2d')
nomads('hrrrak_2d')

• Follow-Ups:
  • Re: [python-users] metpy.parse_cf doesn't set metpy_crs w/ nomads grib2 hrrr ?
    • From: Ryan May