When Does Winter Start? Meteorological vs Astronomical

Meteorological winter in the Northern Hemisphere begins on 1 December and covers December, January and February, the three whole months NOAA and the Met Office use for climate records. Astronomical winter begins at the December solstice: in 2026 that is Monday, 21 December, at 12:49 PM PST (20:49 UTC), about three weeks later.

Key takeaways

• Meteorological winter runs from 1 December to the end of February in the Northern Hemisphere, according to NOAA’s National Centers for Environmental Information (NCEI); in 2026–27 it lasts 90 days.
• Astronomical winter starts at the December solstice: 21 December 2026 at 12:49 PM PST in Encinitas, California (20:49 UTC), and runs to the March equinox on 20 March 2027, about 89 days.
• Whole months make seasonal statistics comparable year to year: NCEI says meteorological seasons last 90 to 92 days, astronomical ones 89 to 93.
• Other calendars start winter earlier: Gaelic Samhain on 1 November and China’s Lidong (“Start of Winter”) on 7 November 2026, with the solstice as midwinter.
• In the Southern Hemisphere everything flips: Australia’s Bureau of Meteorology counts winter as June to August, and the December solstice is midsummer there.

When does winter start: 1 December or the solstice?

Both, depending on who is counting. Weather services start winter on 1 December; astronomers and most printed US calendars start it at the December solstice, on 21 or 22 December.

NCEI, the NOAA office that keeps the US climate record, explains the split: astronomical seasons follow Earth’s position relative to the sun, while meteorological seasons follow the annual temperature cycle and the civil calendar. In the Northern Hemisphere, meteorological winter is December to February. The UK’s Met Office describes the same blocks for Britain: winter runs from December to February.

Why do meteorologists start winter on 1 December?

Because whole months make the numbers comparable. NCEI notes that astronomical seasons change their start dates and lengths from year to year, which makes it hard to compare a season’s climate statistics across years. Meteorological seasons use whole months, last a steadier 90 to 92 days and come straight from monthly data, which NCEI says helps agriculture and commerce.

There is also a physical reason. Winter is often defined by meteorologists as the three calendar months with the lowest average temperatures, and in the Northern Hemisphere those are December, January and February. The coldest weather lags the shortest day by several weeks, so the coldest three months begin before the solstice and run well past it.

Some services go further and let the weather itself decide. Sweden’s national weather service, SMHI, says winter arrives after five consecutive days with a daily mean temperature of 0.0 °C or below, and the start date is the first of those five days.

When is the 2026 December solstice?

The December solstice of 2026 falls on Monday, 21 December 2026, at 12:49 PM Pacific Standard Time in Encinitas, California, which is 20:49 UTC by our ephemeris. The US Naval Observatory lists 20:50 UTC, a rounding difference. In China Standard Time the moment falls on 22 December, which is why the solar term Dongzhi (Winter Solstice) is dated 22 December 2026 in China.

The solstice is the moment the sun reaches its farthest point south, directly over the Tropic of Capricorn, so it brings the shortest day of the year in the Northern Hemisphere. In Encinitas, day length shrinks from 10 h 46 m on 3 November 2026 to 10 h 7 m on 1 December 2026 and 9 h 57 m on 21 December 2026. By convention, the US Naval Observatory notes, solstices and equinoxes are named for Northern Hemisphere seasons.

How do other traditions count the start of winter?

Many older calendars start winter six to seven weeks before the solstice, which then becomes midwinter.

• Gaelic Samhain. In Ireland, Scotland and the Isle of Man, Samhain on 1 November, celebrated from the evening of 31 October, marked the end of the harvest and the beginning of winter. Its history: When Is Samhain, and Did the Celtic Year Begin in the Dark?
• Chinese Lidong. In China’s 24 solar terms, Lidong, which the Hong Kong Observatory translates as “Winter Commences”, begins when the sun reaches 225° of ecliptic longitude. In 2026 that is 7 November (1:51 AM PST). The solstice term Dongzhi follows at 270°. Full explainer: When Is Lidong 2026, the Chinese Start of Winter?

Europe’s older calendars did the same. The Roman writer Varro dated the start of winter to 10 November, with the solstice near its middle, and the Old English Menologium, a late tenth-century verse calendar, starts winter six nights after All Saints’ Day, on 7 November, and calls Christmas midwinter. Calendar drift moved other markers: by the late Middle Ages the Julian calendar put the solstice on about 13 December, St. Lucia Day.

When does winter start in the Southern Hemisphere?

Six months later. Australia’s Bureau of Meteorology uses calendar months too and labels its seasonal outlooks “winter (June to August)”, so meteorological winter there begins on 1 June. Astronomical winter in the south begins at the June solstice. The December solstice is the summer solstice south of the equator, where meteorological summer starts on 1 December.

What does the start of winter mean for keeping time well?

Whichever date you choose, the light changes before the weather does: mornings stay dark longer and evenings start earlier. The body clock takes its strongest daily signal from light: a review in Somnologie (Blume, Garbazza and Spitschan, 2019) explains that light in the morning shifts the body clock earlier and light in the evening shifts it later, and that daylight outdoors is many times brighter than typical indoor lighting.

Two habits carry well across the season. First, keep the wake time steady, including on weekends, so the dark mornings don’t slide your whole day later; how to fix your sleep schedule walks through it. Second, get outside soon after waking, or at the brightest part of the day if it is still dark when you get up. Does winter call for more sleep? See should you sleep more in winter.

Your day on My BodyClock

The day above is a December weekday planned for dark mornings. Sleep runs from 10 PM to 6:30 AM every night, so the wake time stays the same whether the sun rises at 6 AM or near 7 AM. A short wind-up at home leads into a walk outside at first light, then a warm breakfast by the window. Lunch is followed by a midday walk in the brightest part of the day. Evenings dim down: dinner with family, reading under warm lamps and a wind-down before bed.

Build your own version in Owaves, the World’s First Wellness Planner, Powered by Your Body Clock. Take the Body Clock Type quiz, download Owaves on the App Store, or join the Android waitlist.

FAQ

Is the first day of winter 1 December or 21 December?

Both are used. Meteorological winter starts on 1 December and is used by weather services such as NOAA and the Met Office. Astronomical winter starts at the December solstice, which in 2026 falls on 21 December at 12:49 PM PST (20:49 UTC).

When does winter start in Australia?

Australia’s Bureau of Meteorology counts winter as June, July and August, so meteorological winter starts on 1 June. Astronomical winter in the Southern Hemisphere begins at the June solstice, around 20 or 21 June.

Is the winter solstice the shortest day of the year?

Yes, in the Northern Hemisphere. In Encinitas, California, 21 December 2026 has 9 h 57 m of daylight, compared with 10 h 46 m on 3 November 2026. Days start lengthening again after the solstice, though the coldest weather usually comes later.

Sources

1. NOAA National Centers for Environmental Information. Meteorological Versus Astronomical Seasons. Updated 10 March 2023. https://www.ncei.noaa.gov/news/meteorological-versus-astronomical-seasons
2. Met Office. Our seasons (Met Office for Schools). https://weather.metoffice.gov.uk/learn-about/met-office-for-schools/other-content/other-resources/our-seasons
3. US Naval Observatory, Astronomical Applications Department. Earth’s Seasons and Apsides. https://aa.usno.navy.mil/data/Earth_Seasons
4. US Naval Observatory. Earth’s Seasons data service, 2026. https://aa.usno.navy.mil/api/seasons?year=2026
5. SMHI (Swedish Meteorological and Hydrological Institute). Season arrival. https://www.smhi.se/en/weather/observations/season-arrival/vin/2025
6. Bureau of Meteorology, Australia. Climate outlook for winter (June to August). 25 May 2017. https://www.bom.gov.au/climate/ahead/archive/outlooks/20170525-outlook.shtml
7. Hong Kong Observatory. The 24 Solar Terms. https://www.hko.gov.hk/en/gts/time/24solarterms.htm
8. Wikipedia. Winter. https://en.wikipedia.org/wiki/Winter
9. Wikipedia. Samhain. https://en.wikipedia.org/wiki/Samhain
10. Blume C, Garbazza C, Spitschan M. Effects of light on human circadian rhythms, sleep and mood. Somnologie 23(3):147–156 (2019). doi:10.1007/s11818-019-00215-x. https://pmc.ncbi.nlm.nih.gov/articles/PMC6751071/
11. Varro. On Agriculture, Book I.28 (Loeb translation), LacusCurtius. https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Varro/de_Re_Rustica/1*.html
12. Karasawa K. The Old English Metrical Calendar (Menologium). Boydell & Brewer, 2015. https://www.cambridge.org/core/books/old-english-metrical-calendar-menologium/introduction/E217F3316ACE3C704427254E6A05FD8A
13. Byrne A. What’s behind our fascination with Samhain’s haunting legacy? RTÉ Brainstorm, 13 October 2025. https://www.rte.ie/brainstorm/2025/1013/1477988-samhain-halloween-death-unknown-supernatural-ghost-stories-horror-movies/

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