Indian summer

Tafjord in western Norway, enjoyed a startling nightly temperature of 22.6C (72.7F) as the final day of October arrived

Indian summer (also called Old Wives' summer in the United Kingdom) is a name given to a period of sunny, warm weather in autumn, not long before winter. This time is often in late October or early November (Northern hemisphere) / late April or early May (Southern hemisphere), usually sometime after the first frost. It can persist for just a few days or sometimes over a week.