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[python #CWW-995296]: Plotting pygrib file with matplotlib


Well this is a strange one. I found a copy of some similar data here:


Those lines are caused by contours wrapping from the right side of the map 
domain to the left. While this makes sense in some contexts, what's weird here 
is that the longitudes seem to only be going 0->180, and then back around. In 
fact, looking at a single row of longitudes in this data, I saw multiple places 
where it jumped from 0 to -180. I think that's a bug in pygrib. You can work 
around it like I've done in a modified version of your code using 
`numpy.unwrap` (which for future reference is much more easy to work with when 
attached as text rather than a screenshot):

    import pygrib
    import matplotlib
    import matplotlib.pyplot as plt
    import cartopy.crs as ccrs
    import cartopy.feature as cfeature
    import numpy as np

    filename = 'blend.t00z.pop12.oc.grib2'
    read = pygrib.open(filename)

    numbers = read[1]

    lats, lons = numbers.latlons()
    lons2 = np.unwrap(lons, discont=180)

    figure = plt.figure(1, figsize=(14, 14))

    ax = plt.subplot(1, 1, 1, projection=ccrs.PlateCarree())
    ax.set_extent([-130, -65, 20, 55])
    ax.contour(lons2, lats, numbers.values, transform=ccrs.PlateCarree())
    cbar = ax.imshow(numbers.values)


Hope that helps,


> Hello. We are working on a python assignment for our Synoptic Lab. The goal 
> of the assignment is to create a program that plots NBM data on a map, and 
> while we are able to plot data, there are horizontal lines that show up in 
> the output. When trying different forecast hours, or a different parameter 
> for the plot, the amount of lines differs. I have provided screenshots of the 
> code and what the program is outputting. Is there any way that this can be 
> resolved? Thank you.

Ticket Details
Ticket ID: CWW-995296
Department: Support Python
Priority: Low
Status: Closed
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