"Be gloomy" is an expression used to describe a mood or behavior that is dull, desolate, and lacking in cheer. Synonyms for this phrase could include "be despondent," "be melancholy," "be morose," "be sad," "be disheartened," "be dejected," "be depressed," "be somber," "be downhearted," "be depressing," "be pessimistic," and "be heartbroken." These words convey various degrees of sorrow, and can be used interchangeably depending on the context. Whether discussing the weather, emotions, or a person's outlook on life, these synonyms can help provide more nuance to the description of a particularly dreary or downcast situation.