[python #LNM-931708]: GFS metpy cross section plot

Hello! Thanks for reaching out to us and your patience in the mean-time.

I was able to create a (admittedly rough) version of this from your provided 
GFS .nc file that I've attached. You're close! The only thing I needed to 
change was to clean up the units on the input pressure and to specify the 
1000-hPa limit as an xarray DataArray. I did this instead of your manual 
conversion, and then specified the scalar 1000-hPa value as a DataArray using 
the 'plevel' coordinate variable. The provided data file had what appeared to 
be an erroneous 18000-hPa I also needed to remove first. So, all-in-all I have 
this code leading up to the plotting cell:

  # This selects everything but your final 18000-hPa plevel value
  data = data.isel(plevel=slice(0, -1))

  start = (39.5, -126.0)
  end = (39.5, -116.0)
  cross = cross_section(data, start, end)
  temperature, pressure = xr.broadcast(cross['TMP'], cross['plevel'])
  theta = mpcalc.potential_temperature(pressure, temperature)
  cross['Potential_temperature'] = xr.DataArray(theta,
                                                coords=temperature.coords,
                                                dims=temperature.dims,
                                                attrs={'units': theta.units})
  cross['UGRD'].metpy.convert_units('knots')
  cross['VGRD'].metpy.convert_units('knots')
  cross['t_wind'], cross['n_wind'] = 
mpcalc.cross_section_components(cross['UGRD'], cross['VGRD'])
  cross['PRES_surface'].metpy.convert_units('hPa')


and then finally adding in the line nearly as you have it in the plotting cell:

  ax.fill_between(cross['longitude'], cross['plevel'].sel(plevel=1000), 
cross['PRES_surface'], color='sienna')

With that, you can see the result I achieved attached. For your second 
question, our `cross_section` code interpolates along a geodesic line between 
the provided latitudes and longitudes. So, if you plot on the flat PlateCarree 
projection, the line will appear curved. I plotted here with a LambertConformal 
projection as my `data_crs` to represent the line closer to the example on the 
documentation. Remember to transform the inset contours as well!

I hope this gives you something to work with and at least points you in the 
right direction. If there's any further way I can help or perhaps put together 
a more thorough demonstration, don't hesitate to follow up! I appreciate your 
patience, and thanks again for reaching out to us.


All the best,

Drew


> Two Quick questions...I think.  I took this example metpy cross section
> code and verified that it worked for me:
> https://unidata.github.io/MetPy/latest/examples/cross_section.html
> 
> Then I edited a version to work with GFS data, with different labels and
> such and this generally worked!  (after fiddling with units and a few
> details)
> 
> 1) I'd like to add the surface terrain as interpreted by surface pressure,
> which would look something like this for example:
> 
> ( I can't use the code that produced this because it uses a completely
> different custom methodology that I don't understand, not to mention
> different input data format, and I want to transition to metpy standards)
> 
> Here is my new GFS python code:
> 
> 
> And here is the GFS netcdf file that is used for plotting:
> 
> On lines 102-103 of my code I have some logic to show what I think I need
> to do, but which I know is flawed.
> 
> *# color terrain - NEEDS WORK#
> ax.fill_between(cross['longitude'[0],cross['PRES_surface']*.01,1000.,color='sienna',zorder=10)*
> 
> I know I want to "fill_between" the min pressure (1000 or so) and the
> "PRES_surface" at the lat/lon point in the cross section, but I'm
> struggling with how to do this.  I do have "PRES_surface" data as a 2D
> array in my "data".
> Any suggestions how I might go about doing this?
> 
> 2) I think this is easier.  I haven't been able to get my inset plot to
> have a proper projection, and notice the path of cross section is curved a
> bit.
> Any tips to fix that?
> 


Ticket Details
===================
Ticket ID: LNM-931708
Department: Support Python
Priority: Low
Status: Closed
===================
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