Frown, scowl, glower, lower, gloom are comparable when they mean to put on a dark or malignant countenance or aspect.
Frown commonly implies a stern face and contracted brows that express displeasure, disapprobation, anger, or contempt.
Scowl carries an implication of wrinkled drawn-down brows that express ill humor, sullenness, or discontent.
Glower implies a more direct stare or gaze than frown or scowl and carries a stronger connotation of anger, contempt, or defiance.
Lower implies a menacing darkness and sullenness of face or of aspect; the term is used in reference not only to persons but to skies that give promise of a storm.
Gloom ordinarily carries a much stronger implication of gloominess or dejection and a much weaker (often nonexistent) suggestion of threatening than does lower.