changeable weather
Archaic expression for unsettled or changeable weather, literally 'the sky without constancy'. Not used in modern Japanese.
The expression 定めなき空 can be found in classical waka poetry.
The phrase combines 定めなき (archaic negative form of 定める, 'to decide, fix') and 空 ('sky'), literally 'the unfixed sky'. The exact origin is uncertain, but it appears in classical Japanese literature.