minacious

1. threatening or foreshadowing evil or tragic developments

    e.g. a baleful look
           forbidding thunderclouds
           his tone became menacing
           ominous rumblings of discontent
           sinister storm clouds
           a sinister smile
           his threatening behavior
           ugly black clouds
           the situation became ugly

    Synonym: baleful forbidding menacing minatory ominous sinister threatening