From Longman Dictionary of Contemporary Englishstorm cloudˈstorm cloud noun [countable] 1 HEMa dark cloud which you see before a storm2 [usually plural]WARN a sign that something very bad is going to happen Storm clouds are gathering over the trade negotiations.
Examples from the Corpus
storm cloud• But a storm cloud hovered on the horizon.• Animation is fair, but the scene where the dragon flies into a storm cloud and is electrocuted is positively brain-bending!• Her teased black hair surrounded her like a storm cloud. 