Autumn: a burst of colour

When does autumn start?

As with the other seasons, there are two main ways to define the start of autumn:

Meteorological autumn

Always begins on 1 September and ends on 30 November. This system divides the year into four fixed three-month seasons, making it easier to compare weather statistics.

Astronomical autumn

Begins with the autumn equinox, usually around 22 or 23 September, when the Sun shines directly on the equator and day and night are nearly equal in length. The exact dates can vary slightly each year due to the Earth’s orbit.

Sign that autumn has arrived

The start of the season is often recognised by:

• Changing colours: Perhaps the most noticeable sign of autumn is the changing colours of the leaves. As a result of falling temperatures in autumn, the chemical in the leaves that makes them green (chlorophyll) begins to break down while other chemicals (including carotene) remain to give the leaves their yellow, red and brown colours.The most vibrant displays of autumn leaves are evident when a dry summer is followed by an autumn with dry, sunny days and cold, but not freezing, nights.

What is the weather like in autumn?

Autumn is normally associated with dropping temperatures and nights ‘drawing in’ as winter approaches.

• Associated weather conditions: cooler temperatures, shorter days, and often unsettled, stormy weather as winter approaches.
• Shorter days: After the autumn equinox, nights become longer than days until the spring equinox.
• Chance of unsettled weather: In the UK autumn can mean unsettled weather and towards the latter part of the season can bring stormy conditions with strong gales due to Atlantic depressions moving over the UK.
• Average temperature: The average mean temperature for autumn in the UK is 9.71°C, using the long-term average period of 1991-2020.
• Autumn vs. Fall: The word “Fall” was once common in Britain, derived from “fall of the leaf,” but “autumn” (from French) became standard in the 18th century.