<P> Indian summer is a period of unseasonably warm, dry weather that sometimes occurs in autumn in the Northern Hemisphere . The US National Weather Service defines this as weather conditions that are sunny and clear with above normal temperatures, occurring late - September to mid-November . It is usually described as occurring after a killing frost . </P> <P> Late - 19th century Boston lexicographer Albert Matthews made an exhaustive search of early American literature in an attempt to discover who coined the expression . The earliest reference he found dated from 1851 . He also found the phrase in a letter written in England in 1778, but discounted that as a coincidental use of the phrase . </P>

Where does the phrase indian summer come from
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