Declarative show() does not pop up GUI

[dopplershift]

import metpy.plots as mpplots

# Panel for plot with Map features
panel = mpplots.MapPanel()
panel.layout = (1, 1, 1)
panel.area = (-124, -72, 20, 53)
panel.projection = 'lcc'
panel.layers = ['coastline', 'borders', 'states', 'land']

# Bringing it all together
pc = mpplots.PanelContainer()
pc.size = (15, 9)
pc.panels = [panel]

pc.show()

I would have expected this to pop up a GUI window, but it doesn't. You have to call plt.show() to get that.