How you define the first day of winter depends on whether you are referring to the astronomical or meteorological winter.
This year, astronomical winter begins on 21 December 2021 and ends on 20 March 2022.
For upcoming years, the dates for astronomical winter will be:
|Year||Winter Starts||Winter Ends|
|Winter 2021||Tuesday, 21 December 2021|
Sunday, 20March 2022
|Winter 2022||Wednesday, 21 December 2022|
Monday, 20March 2023
|Winter 2023||Friday, 22 December 2023|
Wednesday, 20 March 2024
|Winter 2024||Saturday, 21 December 2024|
Thursday, 20 March 2025
The astronomical calendar determines the seasons due to the 23.5 degrees of tilt of the Earth's rotational axis in relation to its orbit around the Sun. Both Equinoxes and Solstices are related to the Earth's orbit around the Sun. However, the dates of the Equinox and Solstice aren't fixed due to the Earth's elliptical orbit of the Sun.
However, at the Met Office, we often use a meteorological definition of the seasons. By the meteorological calendar, the first day of winter is always 1 December; ending on 28 (or 29 during a Leap Year) February.
Meteorological seasons consist of splitting the seasons into four periods made up of three months each. These seasons are split to coincide with our Gregorian calendar, making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics.
The seasons are defined as spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February).