harbinger

1. N-COUNT Something that is a harbinger of something else, especially something bad, is a sign that it is going to happen. (尤指不祥之事的)先兆[文學性] [usu N 'of' n]

The November air stung my cheeks, a harbinger of winter. 11月的空氣刺痛了我的臉頰，這是冬天要來的先兆。