Cassius interprets the storm as a warning from the heavens against Caesar and his ruling of Rome. Of course, Cassius contrives his interpretation just as Casca has already said men do: "But men may construe things after their fashion, / Clean from the purpose of the things themselves."
In Act 1, Scene 3 of Shakespeare's "Julius Caesar," a horrible storm has taken place, and many have witnessed strange events. Casca is frightened, but he comes upon Cassius, who seems calm. He tells Casca, "heaven hath infused them [the elements of the storm] with these spirits, / To make them instruments of fear and warning / Unto some monstrous state." He goes on to compare Caesar to "a man most like this dreadful night." He wants to convince Casca to join him in the conspiracy to get rid of Caesar.