The rainbow wasn't a good sign in the ANE

Signs are, not surprisingly, integrally related to the specific character of the covenant they are attached to. In the case of the sign of the Noahic covenant, the rainbow comes out after the storm, thus signaling the cessation of the flood. [Footnote: In contrast, when rainbows are attested in celestial divination texts, they are malefic signs in five out of eight occurrences. W. Horowitz, “All About Rainbows,” in Laws of Heaven—Laws of Nature: Legal Interpretations of Cosmic Phenomena in the Ancient World, ed. K. Schmid and C. Uehlinger, OBO 276 (Gottingen: Vandenhoeck and Ruprecht, 2016), 40–51.]—Lost World of the Flood, 106