Winter is the coldest and darkestseason of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures define different dates as the start of winter, and some use a definition based on weather.
When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, and vice versa. Winter typically brings precipitation that, depending on a region's climate, is mainly rain or snow. The moment of winter solstice is when the Sun's elevation with respect to the North or South Pole is at its most negative value; that is, the Sun is at its farthest below the horizon as measured from the pole. The day on which this occurs has the shortest day and the longest night, with day length increasing and night length decreasing as the season progresses after the solstice.
The earliest sunset and latest sunrise dates outside the polar regions differ from the date of the winter solstice and depend on latitude. They differ due to the variation in the solar day throughout the year caused by the Earth's elliptical orbit (see: earliest and latest sunrise and sunset).
Etymology
The English word winter comes from the Proto-Germanic noun *wintru-, whose origin is unclear. Several proposals exist, a commonly mentioned one connecting it to the Proto-Indo-European root *wed- 'water' or a nasal infix variant *wend-.[1]
The tilt of the Earth's axis relative to its orbital plane plays a large role in the formation of weather. The Earth is tilted at an angle of 23.44° to the plane of its orbit, causing different latitudes to directly face the Sun as the Earth moves through its orbit. This variation brings about seasons. When it is winter in the Northern Hemisphere, the Southern Hemisphere faces the Sun more directly and thus experiences warmer temperatures than the Northern Hemisphere. Conversely, winter in the Southern Hemisphere occurs when the Northern Hemisphere is tilted more toward the Sun. From the perspective of an observer on the Earth, the winter Sun has a lower maximum altitude in the sky than the summer Sun.
During winter in either hemisphere, the lower altitude of the Sun causes the sunlight to hit the Earth at an oblique angle. Thus a lower amount of solar radiation strikes the Earth per unit of surface area. Furthermore, the light must travel a longer distance through the atmosphere, allowing the atmosphere to dissipate more heat. Compared with these effects, the effect of the changes in the distance of the Earth from the Sun (due to the Earth's elliptical orbit) is negligible.
The manifestation of the meteorological winter (freezing temperatures) in the northerly snow-prone latitudes is highly variable, depending on elevation, position versus marine winds, and the amount of precipitation. For instance, within Canada (a country of cold winters), Winnipeg, on the Great Plains (a long way from the ocean), has a January high of −11.3°C (11.7°F) and a low of −21.4°C (−6.5°F).[2]
In comparison, Vancouver, on the west coast (with a marine influence from moderating Pacific winds), has a January low of 1.4°C (34.5°F), with days well above freezing, at 6.9°C (44.4°F).[3] Both places are at 49°N latitude and in the same western half of the continent. A similar but less extreme effect is found in Europe: in spite of their northerly latitude, the British Isles lack non-mountain weather stations with a below-freezing mean January temperature.[4]
Meteorological reckoning is the method of measuring the winter season used by meteorologists based on "sensible weather patterns" for record keeping purposes,[5] so the start of meteorological winter varies with latitude.[6] Winter is often defined by meteorologists to be the three calendar months with the lowest average temperatures. This corresponds to the months of December, January and February in the Northern Hemisphere, and June, July and August in the Southern Hemisphere.
The coldest average temperatures of the season are typically experienced in January or February in the Northern Hemisphere and in June, July or August in the Southern Hemisphere. Nighttime predominates in the winter season, and in some regions, winter has the highest rate of precipitation as well as prolonged dampness because of permanent snow cover or high precipitation rates coupled with low temperatures, precluding evaporation. Blizzards often develop and cause many transportation delays. Diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40°C (−40°F) due to air with slightly higher moisture from above mixing with colder, surface-based air.[7] They are made of simple hexagonal ice crystals.[8]
The Swedish Meteorological Institute (SMHI) defines thermal winter as when the daily mean temperatures are below 0°C (32°F) for five consecutive days.[9] According to the SMHI, winter in Scandinavia is more pronounced when Atlantic low-pressure systems take more southerly and northerly routes, leaving the path open for high-pressure systems to come in and cold temperatures to occur. As a result, the coldest January on record in Stockholm, in 1987, was also the sunniest.[10][11]
Accumulations of snow and ice are commonly associated with winter in the Northern Hemisphere, due to the large land masses there. In the Southern Hemisphere, the more maritime climate and the relative lack of land south of 40°S make the winters milder; thus, snow and ice are less common in inhabited regions of the Southern Hemisphere. In this region, snow occurs every year in elevated regions such as the Andes, the Great Dividing Range in Australia, and the mountains of New Zealand, and also in the southerly Patagonia region of South Argentina. Snow occurs year-round in Antarctica.
In the Northern Hemisphere, some authorities define the period of winter based on astronomical fixed points (i.e., based solely on the position of the Earth in its orbit around the Sun), regardless of weather conditions. In one version of this definition, winter begins at the winter solstice and ends at the March equinox.[12] These dates are somewhat later than those used to define the beginning and end of the meteorological winter — usually considered to span the entirety of December, January, and February in the Northern Hemisphere and June, July, and August in the Southern.[12][13]
Astronomically, the winter solstice — being the day of the year that has fewest hours of daylight — ought to be in the middle of the season,[14][15] but seasonal lag means that the coldest period normally follows the solstice by a few weeks. In some cultures, the season is regarded as beginning at the solstice and ending on the following equinox.[16][17] In the Northern Hemisphere, depending on the year, this corresponds to the period between 20, 21 or 22 December and 19, 20 or 21 March.[12]
In an old Norwegian tradition, winter begins on 14 October and ends on the last day of February.[18]
This system of seasons is based on the length of days exclusively. The three-month period of the shortest days and weakest solar radiation occurs during November, December and January in the Northern Hemisphere and May, June and July in the Southern Hemisphere.
Many mainland European countries tended to recognize Martinmas or St. Martin's Day (11 November) as the first calendar day of winter.[25] The day falls at the midpoint between the old Julian equinox and solstice dates. Also, Valentine's Day (14 February) is recognized by some countries as heralding the first rites of spring, such as flowers blooming.[26]
The three-month period associated with the coldest average temperatures typically begins somewhere in late November or early December in the Northern Hemisphere and lasts through late February or early March. This "thermological winter" is earlier than the solstice delimited definition, but later than the daylight (Celtic or Chinese) definition. Depending on seasonal lag, this period will vary between climatic regions.
Since by almost all definitions valid for the Northern Hemisphere, winter spans 31 December and 1 January, the season is split across years, just like summer in the Southern Hemisphere. Each calendar year includes parts of two winters. This causes ambiguity in associating a winter with a particular year, e.g. "Winter 2018". Solutions for this problem include naming both years, e.g. "Winter 18/19", or settling on the year the season starts in or on the year most of its days belong to, which is the later year for most definitions.
Ecological reckoning and activity
The snowshoe hare, and some other animals, change color in winter.
Ecological reckoning of winter differs from calendar-based by avoiding the use of fixed dates. It is one of six seasons recognized by most ecologists who customarily use the term hibernal for this period of the year (the other ecological seasons being prevernal, vernal, estival, serotinal, and autumnal).[27] The hibernal season coincides with the main period of biological dormancy each year whose dates vary according to local and regional climates in temperate zones of the Earth. The appearance of flowering plants like the crocus can mark the change from ecological winter to the prevernal season as early as late January in mild temperate climates.
To survive the harshness of winter, many animals have developed different behavioral and morphological adaptations for overwintering:
Hibernation is a state of reduced metabolic activity during the winter. Some animals "sleep" during winter and only come out when the warm weather returns; e.g., gophers, frogs, snakes, and bats.
Some animals store food for the winter and live on it instead of hibernating completely. This is the case for squirrels, beavers, skunks, badgers, and raccoons.
Resistance is observed when an animal endures winter but changes in ways such as color and musculature. The color of the fur or plumage changes to white (in order to be confused with snow) and thus retains its cryptic coloration year-round. Examples are the rock ptarmigan, Arctic fox, weasel, white-tailed jackrabbit, and mountain hare.
Some fur-coated mammals grow a heavier coat during the winter; this improves the heat-retention qualities of the fur. The coat is then shed following the winter season to allow better cooling. The heavier coat in winter made it a favorite season for trappers, who sought more profitable skins.
Snow also affects the ways animals behave; many take advantage of the insulating properties of snow by burrowing in it. Mice and voles typically live under the snow layer.
Some annual plants never survive the winter. Other annual plants require winter cold to complete their life cycle; this is known as vernalization. As for perennials, many small ones profit from the insulating effects of snow by being buried in it. Larger plants, particularly deciduous trees, usually let their upper part go dormant, but their roots are still protected by the snow layer. Few plants bloom in the winter, one exception being the flowering plum, which flowers in time for Chinese New Year. The process by which plants become acclimated to cold weather is called hardening.
1683–1684, "The Great Frost", when the Thames, hosting the River Thames frost fairs, was frozen all the way up to London Bridge and remained frozen for about two months. Ice was about 27cm (11in) thick in London and about 120cm (47in) thick in Somerset. The sea froze up to 2 miles (3.2km) out around the coast of the southern North Sea, causing severe problems for shipping and preventing use of many harbors.
1739–1740, one of the most severe winters in the UK on record. The Thames remained frozen over for about 8 weeks. The Irish famine of 1740–1741 claimed the lives of at least 300,000 people.[28]
1816 was the Year Without a Summer in the Northern Hemisphere. The unusual coolness of the winter of 1815–1816 and of the following summer was primarily due to the eruption of Mount Tambora in Indonesia, in April 1815. There were secondary effects from an unknown eruption or eruptions around 1810, and several smaller eruptions around the world between 1812 and 1814. The cumulative effects were worldwide but were especially strong in the Eastern United States, Atlantic Canada, and Northern Europe. Frost formed in May in New England, killing many newly planted crops, and the summer never recovered. Snow fell in New York and Maine in June, and ice formed in lakes and rivers in July and August. In the UK, snow drifts remained on hills until late July, and the Thames froze in September. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in food shortages and the worst famine of the 19th century.
1887–1888: There were record cold temperatures in the Upper Midwest, heavy snowfalls worldwide, and amazing storms, including the Schoolhouse Blizzard of 1888 (in the Midwest in January) and the Great Blizzard of 1888 (in the Eastern US and Canada in March).
In Europe, the winters of early 1947,[29] February 1956, 1962–1963, 1981–1982, and 2009–2010 were abnormally cold. The UK winter of 1946–1947 started out relatively normal but became one of the snowiest UK winters to date, with nearly continuous snowfall from late January until March.
In South America, the winter of 1975 was one of the strongest, with record snow occurring at 25°S in cities of low altitude, with the registration of −17°C (1.4°F) in some parts of southern Brazil.
In the eastern United States and Canada, the winter of 2013–2014 and the second half of February 2015 were abnormally cold.
1310–1330: Many severe winters and cold, wet summers in Europe, the first clear manifestation of the unpredictable weather of the Little Ice Age that lasted for several centuries (from about 1300 to 1900). The persistently cold, wet weather caused great hardship, was primarily responsible for the Great Famine of 1315–1317, and strongly contributed to the weakened immunity and malnutrition leading up to the Black Death (1348–1350).
1690s: Extremely cold, snowy, severe winters. Ice surrounded Iceland for miles in every direction.
1779–1780: Scotland's coldest winter on record, and ice surrounded Iceland in every direction (like in the 1690s). In the United States, a record five-week cold spell bottomed out at −20°F (−29°C) in Hartford, Connecticut and −16°F (−27°C) in New York City. The Hudson River and New York's harbor froze over.
1783–1786: The Thames partially froze, and snow remained on the ground for months. In February 1784, the North Carolina was frozen in Chesapeake Bay.
1794–1795: A severe winter, with the coldest January in the UK and lowest temperature ever recorded in London: −21°C (−6°F) on 25 January. The cold began on Christmas Eve and lasted until late March, with a few temporary warm-ups. The Severn and Thames froze, and frost fairs started up again. The French army tried to invade the Netherlands over its frozen rivers, while the Dutch fleet was stuck in its harbor. The winter had easterlies (from Siberia) as its dominant feature.
1813–1814: Severe cold, last freeze-over of Thames, and last frost fair. (Removal of old London Bridge and changes to river's banks made freeze-overs less likely.)
1883–1888: Colder temperatures worldwide, including an unbroken string of abnormally cold and brutal winters in the Upper Midwest, related to the explosion of Krakatoa in August 1883. There was snow recorded in the UK as early as October and as late as July during this period.
1976–1977: One of the coldest winters in the US in decades.
1985: Arctic outbreak in the US resulting from shift in polar vortex, with many cold temperature records broken.
2002–2003 was an unusually cold winter in the Northern and Eastern US.
2010–2011: Persistent bitter cold in the entire eastern half of the US from December onward, with few or no midwinter warm-ups, and with cool conditions continuing into spring. La Niña and negative Arctic oscillation were strong factors. Heavy and persistent precipitation contributed to almost constant snow cover in the Northeastern US, which finally receded in early May.
2011 was one of the coldest on record in New Zealand, with sea level snow falling in Wellington in July for the first time in 35 years and a much heavier snowstorm for 3 days in a row in August.
Effect on humans
People enjoying the winter weather outdoors in Helsinki, Finland
Humans are sensitive to winter cold, which compromises the body's ability to maintain both core and surface heat of the body.[30] Slipping on icy surfaces is a common cause of winter injuries.[31] Other injuries from the cold include:[32]
Hypothermia — Shivering, leading to uncoordinated movements and death.
Frostbite — Freezing of skin, leading to loss of feeling and damaged tissue.
Trench foot — Numbness, leading to damaged tissue and gangrene.
Chilblains — Capillary damage in digits can lead to more severe cold injuries.
Rates of influenza, COVID-19, and other respiratory diseases also increase during the winter.[33][34]
In Persian culture, the winter solstice is called Yaldā (meaning: birth) and has been celebrated for thousands of years. It is referred to as the eve of the birth of Mithra, who symbolised light, goodness and strength on Earth.
In Greek mythology, Hades kidnapped Persephone to be his wife. Zeus ordered Hades to return her to Demeter, the goddess of the Earth and her mother. Hades tricked Persephone into eating the food of the dead, so Zeus decreed that she spend six months with Demeter and six months with Hades. During the time her daughter is with Hades, Demeter became depressed and caused winter.
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole.
The subarctic climate is a continental climate with long, cold winters, and short, warm to cool summers. It is found on large landmasses, often away from the moderating effects of an ocean, generally at latitudes from 50°N to 70°N, poleward of the humid continental climates. Like other Class D climates, they are rare in the Southern Hemisphere, only found at some isolated highland elevations. Subarctic or boreal climates are the source regions for the cold air that affects temperate latitudes to the south in winter. These climates represent Köppen climate classification Dfc, Dwc, Dsc, Dfd, Dwd and Dsd.
1816 is known as the Year Without a Summer because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1 °F). Summer temperatures in Europe were the coldest of any on record between 1766 and 2000, resulting in crop failures and major food shortages across the Northern Hemisphere.
Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June and December.
Seasonal lag is the phenomenon whereby the date of maximum average air temperature at a geographical location on a planet is delayed until some time after the date of maximum daylight. This also applies to the minimum temperature being delayed until some time after the date of minimum insolation. Cultural seasons are often aligned with annual temperature cycles, especially in the agrarian context. Peak agricultural growth often depends on both insolation levels and soil/air temperature. Rainfall patterns are also tied to temperature cycles, with warmer air able to hold more water vapor than cold air.
A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criteria for a cold wave are the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year.
The winter of 1962–1963, known as the Big Freeze of 1963, was one of the coldest winters on record in the United Kingdom. Temperatures plummeted and lakes and rivers began to freeze over.
The winter of 1894–1895 was severe for the British Isles with a Central England temperature (CET) of 1.17 °C or 34.1 °F. Many climatologists have come to view this winter as the end of the Little Ice Age and the culmination of a decade of harsh winters in Britain. Whereas the average CET for the 10 winters from 1885–1886 to 1894–1895 was 2.87 °C or 37.2 °F, no winter with a CET under 3.0 °C or 37.4 °F followed for 22 years and no month as cold as February or January 1895 until 1940. In contrast, between 1659 and 1894, no spell with every winter CET above 3.0 °C or 37.4 °F had lasted longer than 12 winters.[b]
The summer solstice or estival solstice occurs when one of Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere. The summer solstice is the day with the longest period of daylight and shortest night of the year in that hemisphere, when the sun is at its highest position in the sky. At either pole there is continuous daylight at the time of its summer solstice. The opposite event is the winter solstice.
The climate of the Arctic is characterized by long, cold winters and short, cool summers. There is a large amount of variability in climate across the Arctic, but all regions experience extremes of solar radiation in both summer and winter. Some parts of the Arctic are covered by ice year-round, and nearly all parts of the Arctic experience long periods with some form of ice on the surface.
The equator is a circle of latitude that divides a spheroid, such as Earth, into the Northern and Southern hemispheres. On Earth, the Equator is an imaginary line located at 0 degrees latitude, about 40,075 km (24,901 mi) in circumference, halfway between the North and South poles. The term can also be used for any other celestial body that is roughly spherical.
The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice, while in the Southern Hemisphere it is the winter solstice. It is also known as the northern solstice. During June solstice, the Sun is directly over the Tropic of Cancer, located in the northern hemisphere.
The December solstice, also known as the southern solstice, is the solstice that occurs each December – typically on 21 December, but may vary by one day in either direction according to the Gregorian calendar. In the Northern Hemisphere, the December solstice is the winter solstice, whilst in the Southern Hemisphere it is the summer solstice. During December solstice, the Sun is directly over the Tropic of Capricorn, located in the Southern Hemisphere.
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historical definitions of the seasons.
The south of Sweden has a temperate climate, despite its northern latitude, with largely four distinct seasons and mild temperatures throughout the year. The winter in the far south is usually weak and is manifested only through some shorter periods with snow and sub-zero temperatures, autumn may well turn into spring there, without a distinct period of winter. The northern parts of the country have a subarctic climate while the central parts have a humid continental climate. The coastal south can be defined as having either a humid continental climate using the 0 °C isotherm, or an oceanic climate using the –3 °C isotherm.
The 2015–16 North American winter was not as frigid across North America and the United States as compared to the 2013–14 and 2014–15 winters. This was mainly due to a strong El Niño, which caused generally warmer-than-average conditions. However, despite the warmth, significant weather systems still occurred, including a snowstorm and flash flooding in Texas at the end of December and a large tornado outbreak at the end of February. The main event of the winter season, by far and large, was when a crippling and historic blizzard struck the Northeastern United States in late January, dumping up to 3 feet of snow in and around the metropolitan areas. Several other smaller snow events affected the Northeast as well, but for the most part the heaviest snowstorms and ice stayed out further west, such as a severe blizzard in western Texas in late December, and a major late-season snowstorm in Colorado in mid-April.
Sweden had a very unusual start and finish to the year 2010, with two consecutive winter cold waves occurring in a single calendar year. Since both events were notable, both are covered in this article.
The 2017–18 North American winter saw weather patterns across North America that were very active, erratic, and protracted, especially near the end of the season, resulting in widespread snow and cold across the continent during the winter. Significant events included rare snowfall in the South, an outbreak of frigid temperatures that affected the United States during the final week of 2017 and early weeks of January, and a series of strong nor'easters that affected the Northeastern United States during the month of March. In addition, flooding also took place during the month of February in the Central United States. Finally the winter came to a conclusion with a powerful storm system that caused a tornado outbreak and blizzard in mid-April. The most intense event, however, was an extremely powerful cyclonic blizzard that impacted the Northeastern United States in the first week of 2018. Similar to the previous winter, a La Niña was expected to influence the winter weather across North America.
The 2018–19 European winter occurred from late 2018 to early 2019. Notable events included the early snows in Spain and intense flooding in Italy, in cities such as Venice, the intense snow storms which affected central Europe in January, the snow storms in Greece over the New Year period, as well as the end of February. As well as severe winter weather, there was also exceptional warmth across western Europe in the last week of February. Parts of France had their warmest February day on record, with temperatures up to 28.1 °C (82.6 °F) at Eus on the 27th. Many places in the United Kingdom also broke temperature records, including the national record in Kew Gardens, at 21.2 °C (70.2 °F) on the 26th. Unlike previous winters, a developing El Niño was expected to influence weather patterns across Europe, although the effect is not fully known.
The 2019–20 North American winter was unusually warm for many parts of the United States; in many areas, neutral ENSO conditions controlled the weather patterns, resulting in strong El Niño like conditions and the sixth-warmest winter on record, and many areas in the Northeastern United States saw one of the least snowy winters in years. In fact, Baltimore and Islip saw no snow in February for the first time. Some notable events still occurred, such as a powerful blizzard that impacted the Western United States in late November, a series of cold shots in January and February, a snowstorm within the Texas Panhandle and a late-season blizzard in the High Plains.
↑ "winter". Encyclopædia Britannica. 16 September 2022. Retrieved 28 October 2022.
↑ "solstice". Encyclopædia Britannica. Retrieved 28 October 2022.
↑ "Første vinterdag". The Norwegian Meteorological Institute (in Norwegian). 14 October 2008. Archived from the original on 29 June 2011. Retrieved 31 August 2009.
↑ "Seasons". Meteorological Glossary. Australian Bureau of Meteorology. Archived from the original on 7 March 2009. Retrieved 21 June 2009.
↑ Anderson, Earl R. (2003). Folk-Taxonomies in Early English. Madison, N.J.: Fairleigh Dickinson University Press. p.219. ISBN978-0-8386-3916-0. On St. Martin's day (11 November) winter begins, summer takes its end, harvest is completed. ...This text is one of many that preserves vestiges of the ancient Indo-European system of two seasons, winter and summer.
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