an Indian summer

Indian summer

1. A period of unseasonably warm weather in early fall. I know it's September, but don't get out your winter clothes just yet—this area often has an Indian summer. I hate the cold weather, so I'm hoping for an Indian summer.
2. A particularly peaceful, successful, or enjoyable time as something nears its end. As her illness worsened, my grandmother still enjoyed painting, so I think she had an Indian summer before her death. I wonder if people sensed that they were in an Indian summer just before the Great Depression.
See also: Indian, summer
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

an Indian summer

mainly BRITISH
An Indian summer is a period of great success late in someone's life or career, often after a period of not being successful. Despite an unexpected Indian Summer, they never really lived up to their initial promise. Note: An Indian summer is a period of unusually warm sunny weather during the autumn.
See also: Indian, summer
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012

an ˌIndian ˈsummer

1 a period of unusually dry, warm weather in the autumn: We had a splendid Indian summer last October.
2 a period of success or happiness near the end of somebody’s life: He made his best movies in his seventies; it was for him a real Indian summer.
See also: Indian, summer
Farlex Partner Idioms Dictionary © Farlex 2017
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References in classic literature ?
But as the last two days had been very warm, like an Indian summer, the ice was not now transparent, showing the dark green color of the water, and the bottom, but opaque and whitish or gray, and though twice as thick was hardly stronger than before, for the air bubbles had greatly expanded under this heat and run together, and lost their regularity; they were no longer one directly over another, but often like silvery coins poured from a bag, one overlapping another, or in thin flakes, as if occupying slight cleavages.
WALES can look forward to an Indian summer next week with temperatures reaching highs of 19degC, forecasters say.
but not before an Indian summer? NORTH Wales looks set to avoid an "Arctic blast" this autumn as hopes of an Indian summer are raised by forecasters.
A spell of warmer than expected weather in early autumn is often referred to as an Indian summer.
And a week later, Soho House in Handsworth plays host to an Indian Summer Night with a screening of Slumdog Millionaire.
"An Indian summer is when it's much warmer than average after the first frost of the year."
British Weather Services senior meteorologist Jim Dale added: "Just when you thought summer was all over, an Indian summer is incoming.
AFTER a wet summer, the North East could finally be getting some sunshine - but don't call it an Indian Summer.
Called An Indian Summer, the initiative begins with a recruitment drive at 21 universities around the UK, a life size model elephant is used to attract attention, and following a selection round at the students' local Indian restaurant, successful students take part in a 24 hour fund raising challenge.
The Met Office said that while it will be unseasonably hot, it is not an 'Indian summer', as some reports have suggested, as it is too early in the year: "An Indian summer is defined as a warm, calm spell of weather occurring after the first frost in autumn, especially in October and November," it said.
Shame, for an Apache frost and an Indian summer somehow balance the weather lore books rather splendidly!
EXPECTATIONS of sunshine and long hot days may have been washed away by record rainfall this summer, but gardeners as nature's greatest optimists, have high hopes for an Indian Summer.
Meanwhile, we'll look for an Indian summer soon, to tide us over.