fair weather vs conditions

fair weather and conditions both are nouns.

Word	Noun	Adjective	Verb	Adverb
fair weather	Yes	No	No	No
conditions	Yes	No	No	No

As nouns, conditions is a hypernym of fair weather; that is, conditions is a word with a broader meaning than fair weather:

fair weather: moderate weather; suitable for outdoor activities
conditions: the atmospheric conditions that comprise the state of the atmosphere in terms of temperature and wind and clouds and precipitation

Other hypernyms of fair weather include atmospheric condition, weather, weather condition.

fair weather (noun)	conditions (noun)
moderate weather; suitable for outdoor activities	the atmospheric conditions that comprise the state of the atmosphere in terms of temperature and wind and clouds and precipitation
	the set of circumstances that affect someone's welfare
	the prevailing context that influences the performance or the outcome of a process