Question

Sc. 1, Lines 50–61: Who does Macbeth say can set loose these storms?

Answer 1

Macbeth says the witches can set  loose the storms.

In Act 4, Scene 1, Macbeth is speaking to the witches, demanding answers and more prophecies when he says:
"Though you untie the winds and let them fight"
He then provides examples of the damage he knows the storms could do when the witches let the winds loose.