WordNet (r) 3.0 (2006):

weather eye
    n 1: vigilant attentiveness; "he keeps a weather eye open for
         trouble" [syn: watchfulness, vigilance, weather eye]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "weather eye":
   X-ray eye, custodianship, custody, eagle eye, gimlet eye, guard,
   guardedness, guardianship, invigilation, keen eye, lookout,
   monitoring, observance, peeled eye, penetrating eye, proctoring,
   prudence, qui vive, sea legs, seamanlikeness, seamanliness,
   seamanship, sharp eye, shipmanship, stewardship, surveillance,
   vigil, vigilance, wariness, watch, watch and ward, watchful eye,
   watchfulness, watching