Because the weatherman you seein' ain't creating the weather
This line serves to represent two things:
The weatherman is a symbol for the government of Metropolis. The weather is the propaganda that they disseminate to the citizens. Much like the weather is inaccurately portrayed (or predicted), the propaganda is false information used to brainwash the citizens of Metropolis.
The weatherman also may represent the pawns used by the government to gain trust from Metropolis' citizens. By using a non-governmental figure to disseminate the propaganda, the citizens are more likely to trust that which the government tells them or may believe it is not the government at all that is inventing the information.
“Weather” may additionally reference Cindy’s surname, “Mayweather.” If this reference is intended, the line could mean that Cindi’s actions (“the weather”) could not have been predicted or may not be stopped by the government (“the weatherman”).
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