WordNet (r) 3.0 (2006):

fair weather
    n 1: moderate weather; suitable for outdoor activities [syn:
         fair weather, sunshine, temperateness]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "fair weather":
   Saturnia regna, Saturnian age, age of Aquarius, bright side,
   brightness, broiling sun, calm weather, canicular days,
   cheerfulness, climate, clime, cold weather, dog days,
   era of prosperity, forces of nature, golden age, golden era,
   golden time, good times, good weather, halcyon days, heat wave,
   heaven, heyday, high summer, hot wave, hot weather, humid weather,
   macroclimate, microclimate, midday sun, midsummer, millennium,
   muggy weather, palmy days, piping times, prosperity, rainy weather,
   reign of Saturn, rosy era, stormy weather, stuffy weather,
   sultry weather, summer, sunniness, sunny side, sunshine,
   sunshiny weather, the elements, utopia, vertical rays,
   warm weather, weather, windiness