From The Openness of God:

These incidents indicate that human intercession can influence God’s actions. They show that God’s intentions are not absolute and invariant; he does not unilaterally and irrevocably decide what to do. When God deliberates, he evidently takes a variety of things into account, including human attitudes and responses. Once he formulates his plans, they are still open to revision. This appears to be true of even the most emphatic assurances on God’s part.