Indian summer 
noun
1A period of unusually dry, warm weather occurring in late autumn.Soon it was time to climb up the large stone steps, warm from the Indian summer sunlight and less intimidating now that Elise knew what lay within the labyrinthine caverns....
- With an Indian summer (a late warm spell), the ice lost its beauty.
- In Indian summers, when the weather is still good enough to sit out, it's great to have some pots on your patio full of plants with rich, warm colours.
1.1A period of happiness or success occurring late in life.Her 17 year marriage to my father had been conducted in an almost constant state of war, but her short marriage to James had been like an Indian summer of happiness for her....
- But signs of decay were increasingly apparent and the extravagance of the Edwardian period had all the hallmarks of an Indian summer.
- His recent demise has created an almost unprecedented interest in his previous recordings after a late Indian summer that saw so many fine discs of the central German repertoire.