angry clouds, black cat, black clouds, blackening, blocking the light, breakers ahead, broken mirror, cardhouse, cause for alarm, clouding, crisis, danger, danger sign, dangerous ground, darkening, dimming, early symptom, eclipsing, emergency, endangerment, extinguishment, falling barometer, gaping chasm, halcyon bird, hazard, high sign, house of cards, imperilment, jeopardy, menace, obfuscation, obnubilation, obscuration, obscurement, obumbration, occulting, omen, overcast, overclouding, overshading, overshadowing, overshadowment, owl, pass, peril, pinch, plight, precursor, predicament, preliminary sign, premonitory sign, premonitory symptom, prodroma, prodrome, quarantine flag, quicksand, rainbow, raven, red flag, red light, risk, rocks ahead, shading, shadowing, shooting star, skull and crossbones, storm clouds, storm petrel, stormy petrel, strait, symptom, thin ice, threat, thundercloud, thunderhead, warning sign, warning signal, yellow flag, yellow jack