Summer weather during autumn

Some people refer to this kind of weather as an 'Indian summer', but this isn't a formal meteorological term. So where does this expression come from?

The Met Office Meteorological Glossary first published in 1916, defines it as 'a warm, calm spell of weather occurring in autumn, especially in October and November.'

Where does the phrase come from?

There is a complicated and unclear history of the exact origins of the phrase and like many other organisations, we choose not to use the expression. The original source of the phrase is uncertain, several writers have speculated it may originally have referred to a spell of warm, hazy autumn conditions that enabled Indigenous Americans to continue hunting.

Whatever the origin of the phrase, it evidently first was used in the eastern United States. The first recorded use of the phrase appears in a letter written by a Frenchman called John de Crevecoeur dated 17 January 1778. In his description of the Mohawk country he writes "Sometimes the rain is followed by an interval of calm and warm which is called the Indian summer."

The term was first used in the UK in the early 19th century and went on to gain widespread usage. The concept of a warm autumn spell though was not new to the UK. Previously, variations of "Saint Martin's summer" were widely used across Europe to describe warm weather surrounding St Martin's Day (11 November).

What about temperatures?

Despite the basis of these phrases around particular dates, there is no statistical evidence to suggest that such warm spells recur at any particular time each year - warm spells during the autumn months are not uncommon.

Currently, the warmest recorded temperatures in the UK in October and November are 29.9 °C on 1 October 2011, in Gravesend, Kent, and 22.4 °C on 1 November 2015, at Trawsgoed, Ceredigion.