Answer: thundercloud

AnswerCrossword Clue
THUNDERCLOUDSign of bad weather
THUNDERCLOUDBillowy boomer
THUNDERCLOUDBillowy, ominous boomer
thunderclouda cloud charged with electricity and producing lightning and thunder
thundercloudSomething ominous
thundercloudA cumulus cloud with a towering or spreading top, charged with electricity and producing thunder and lightning