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Have a look at the supplied Python script plot_max_value_locations.py and execute it. It shows one way to plot the locations of the highest values, by masking off the lower values as invalid. Another way would be a customised Contouring icon that only plotted large values.
Compute and plot a time series from a point
Look at the supplied script plot_time_series.py as an example. It takes a GRIB file containing temperature data on multiple vertical levels for multiple time steps. The script plots a time series for each level for a given grid point.