A bad omen. A sign of bad things to come. A sign of bad weather. Comes from the New England expression: "Red sky at night, sailor's delight. Red sky in the morning, sailor's warning." This referred to the belief that the sky's color was a predictor of the good or bad weather soon to come.
Maria looked at the crimson sky and remarked, "Uh ohh. Red sky in the morning. Maybe we should cancel today's picnic."
by redskyatnight June 6, 2014