Not sure if this is what you want, but you can add suptitle or text and set the following for different fonts:
plt.title('Mean WRFv3.5 LHF\n', fontsize=40) plt.suptitle('(September 16 - October 30, 2012)\n', fontsize=18) plt.text(0.5, 1, 'the third line', fontsize=13, ha='center')

Hope this helps.
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