White Christmas (weather event)
Of white Christmas is when on Christmas Eve (December 24), on Christmas Day (December 25) and on Boxing Day (December 26) or at least at some point during this time either falling snow or snow .
Meteorological background
The idea of a white Christmas is closely related to Christmas carols such as O Tannenbaum ("... even in winter when it snows ...") or the snow trickles softly and, based on Europe, has led to a global prototype of what the Christmas holidays should look like. At the historical birth of Jesus of Nazareth in Palestine , which is commemorated at Christmas, there was very probably no snow.
Every year, the forecast of snow conditions at Christmas is the topic of the weather forecast . In meteorological terms , a white Christmas means that a closed snow cover is to be found, which generally means at least 1–2 cm of snow depth, and that it does not disappear over the holidays , or that the precipitation takes place as snow ( snow day ), and it is cold enough that this remains in place ( air or at least floor temperature around 0 ° C ). Is there only a broken snow cover or is the snow only temporarily - so it is a " snow cover day " (meteorologically on the cut-off date in the morning, when it is coldest during the day, no measurements are taken at other times, but there are also gaps in snow cover and below 1 cm) - or if one of the days is at least a snowfall day (occurrence of snowfall sometime during the day), the Christmas days are only halfway “white”, otherwise rather “green”, as they say.
To do this, the frost line (0 degree limit), or at least the snow line (falling snow does not thaw to rain, around 4 ° C) must be low enough and remain low enough. In order for there to be snow, the weather on Christmas days or the days leading up to Christmas (later Advent ) must have been favorable: If the snow conditions are good before Christmas, even a short-term heat breakdown cannot resolve it. For snow to fall, the weather must be right for Christmas.
Therefore, the probability of a white Christmas depends on the general weather conditions , the weather of the Christmas holidays as well as the local weather and altitude or other cofactors of precipitation, such as wind conditions . Circumstances such as an intense snowless onset of winter , which freezes the ground well, followed by extensive snowfall, then a pre-Christmas high pressure phase with cold that solidifies the ceiling through sunshine, or through repeated rain / frost periods would be favorable. “Really perfect white Christmas” would be “where it snows on the 24th that the snow stays there on the 25th”, or “snow on all three Christmas days”. The probability of a white Christmas - by definition of a closed snow cover - in Germany is around 12.5 percent and statistically only occurs every 8 years - more often, however, at 30–50 percent over the low mountain ranges and above around 800–1,000 meters are white Christmas secured with a high probability. In the Swiss Central Plateau from 1931 to 2015, the probability that there was a snow cover of at least 1 cm on at least one Christmas day was 40 percent ( Bern ) and 41 percent ( Zurich ).
In addition to the general forecast of weather conditions, which today is absolutely reliable thanks to computational models, especially due to the front systems of weather changes (i.e. relatively chaotic conditions), which are the most difficult to calculate in terms of timing and intensity when arriving at a certain location , the forecast is problematic . In addition, the determination of the zero degree limit is not very precise locally. The combination of the reference date and the thermal limit of the frost point makes the prediction of a white Christmas one of the more complex questions in meteorology. Exceptions are stable, cold high altitudes with already existing snow, as is typical for continental locations , where the question of a white Christmas is relatively marginal.
The expectations of a white Christmas also differ from region to region: While one expects extensive snow conditions in the Alpine region (1 cm of snow is "sugared", but not a real "snow condition" in the local sense), in England, with its mild winter climate, people tend to bet, whether there is at least one snowflake at one point in the 24 hours of December 25th . The date also depends on regional customs. In some regions the main celebration time is the afternoon of Christmas Eve with the Christ Vespers , in other regions the time between the giving of presents in the evening and Christmas mass at midnight, in other regions Christmas Day itself (December 25th).
Historical development and explanatory approaches
Historically, in the middle modern period (17th / 18th century, Baroque ) white Christmas was the rule; this intermediate cold phase is called the Little Ice Age , and the idea of a cold, snowy Christmas was neither worth mentioning nor enjoyable.
Only after the end of the Little Ice Age in the middle of the 19th century (late Romanticism ) did the topic seem to have become topical (the Biedermeier period was still overshadowed by severe winters after the Tambora volcanic eruption in 1815). According to a hypothesis by the Swiss climate researcher Martine Rebetez , the general idea of a white Christmas emerged in European folklore from the mid-19th century. The first Christmas card , printed in London in 1843, shows a celebrating group of people framed by branches and vines, a motif that ranges from timeless to autumn. A map from 1845 shows Santa Claus next to a chimney and the snow-free roofs of the city around him. In contrast, a similar map from 1863 shows large amounts of snow. A study of Christmas customs in many illustrated books showed no snow before 1850. This appeared between 1850 and 1860, was an exception at the time, but became the rule afterwards. At the same time, especially among the British, the fashion emerged of traveling on discovery tours to the wintry Alps on Christmas days, for example to Davos , where there is usually snow. Another influence is likely to come from New England in the United States, where there is often plenty of snow at Christmas. Emigrants of German and English origin found this fascinating and sent Christmas cards with appropriate motifs to their relatives in Europe. In the middle of the 19th century, the image of the snowman changed from the sometimes terrifying bogeyman who was pelted with snowballs by children, to today's winter fun. Even in nativity scenes in the course of the 19th century, it was not the Holy Land itself, but snow-covered Central Europe that was increasingly depicted, similar to the snow-covered tree with tinsel in Christmas decorations .
From weather records from the turn of 19/20. Century has already proven that one was amazed at the increasingly mild December. During this time, Christmas carols with an explicit reference to snow, such as softly trickling snow, were written ( Ebel 1895).
In the 1940s, the Christmas heat drop was defined as a Central European singularity (regular peculiarity) of the turn of early winter / high winter , at that time the white Christmas was already canceled frequently. Ever since the song White Christmas ( I. Berlin 1947), probably the best-selling single of all time, the idea of the snowy Christmas festival applies worldwide. In the 1960s there was a series of particularly snowy winters in the Alps as well as North America, with which the white Christmas is increasingly being advertised as a quality criterion for a destination in the context of winter tourism and winter sports .
Regional
Europe
Before Christmas, temperatures would have to be around freezing point and winds from north to north-westerly, which means that damp and cold air masses seep in from the polar regions , which, when mixed from the west with damp and mild Atlantic air , lead to snow. If a cold east or north-east position follows , the snow will hold up. In Central Europe, the singularity of the Christmas thaw is the rule today , as it goes back to the Schmauß model from the 1920s and defined by Flohn in the 1940s. This is a regular ingress of mild Atlantic air masses ( Atlantic low ), mostly in a west-south-westerly direction, which can cause snow in the previous cold (e.g. a stable high in Russia ), but through abnormal heat consistently lead to a thaw and destroy a white Christmas. This general weather situation is controlled by the Icelandic low and the Azores high , two other important action centers of European weather events. If these dominate the Russia high, a Christmas thaw is more likely. The Atlantic lows are strongly influenced by the Gulf Stream , the "heat pump of Europe".
In the 2000s, the probability of a white Christmas for the lowlands of Central Europe is around 20 to 30%, i.e. only two to three times per decade. Snowfall is much rarer than a closed snow cover.
- Measurement data only partially comparable:
- (a0)Altitude of the weather station until 2010: 1450 m above sea level. A.
- (a1)closed snow cover on December 25th; Values rounded to 5; 1991-2010 data
- (a2)Snowfall on the 24th and fresh snow cover on December 25th; Values rounded to 5; 1991-2010 data
- (a3)closed snow cover on December 24th or 25th; Values rounded to 5; 1991-2013 data
- (a4)Day with snow on December 24th; Data 1951-2014
- (c1)at least 1 cm of snow on at least one of the Christmas days (in brackets: snow on all three Christmas days); Dates 1931-2011
- (d1)on December 24th, 25th or 26th at least a 1 cm thick blanket of snow; Dates 1948-2011
- (e0)December 25th Snow is widespread (in brackets: at least one measuring point); Snow falls (in brackets: at least one snowflake); Dates 1950-2010; similar for Ireland
- (n1)Snow conditions without exact date; Dates 1901-2011
- (s0)Snow conditions without precise information, location approx .; Dates 1931-1980
North America
The climate of North America is characterized by the lack of a west-east barrier, but the pronounced climatic divide of the Cordilleras , which seals off almost the entire continent from the west wind drift. Therefore, polar cold air can flow southwards unhindered, and both from the northwest (controlled by the Aleutian Deep ) and from the south from the Caribbean, humid frontal systems migrate over the land mass, while the interior is characterized by the dryness in the lee. The Hudson Bay as “America's icebox” reaches deep into the interior, the Great Lakes act there as a climate divide . On the Atlantic coast, the cold Labrador Current reverses the precipitation-to-temperature gradient until it meets the warm Gulf Stream off North Carolina, so that the north is drier than the south. The Azores high as the “weather engine” of the North Atlantic - even in winter - can shift quite close to North America. This leads to the extreme weather in North America, and there are various large-scale weather scenarios for a white Christmas in question, from Nor'easter to blizzards to Caribbean lows accumulating in stable cold air . The west coast, on the other hand, is strictly oceanic, and the temperatures shift almost 20 ° to the north: Alaska's south and west coast (latitudes like Scandinavia) have roughly the same conditions as Newfoundland (latitudes like Central Europe). Here Aleutentief and Japanstrom / North Pacific Current control the winter climate, which channel the heat far north, similar to Europe.
The odds of a White Christmas range from under 10% for the entire southern half of the United States and the entire west coast to almost Alaska to over 90% west of the Great Lakes and New England. Only the permafrost regions of the far north of Canada are definitely white.
| Measurement location, area | country |
Altitude in m |
Snow cover in% |
|---|---|---|---|
| Vancouver , British Columbia | CA | 10 | 11 |
| Calgary , Alberta | CA | 1048 | 56 |
| Winnipeg , Manitoba | CA | 238 | 98 |
| Toronto , Ontario | CA | 76 | 36 |
| Ottawa , Ontario | CA | 70 | 81 |
| Québec , Québec | CA | 5 | 98 |
| Whitehorse , Yukon | CA | - | 100 |
| Iqaluit , Nunavut | CA | 3 | 100 |
| Anchorage , Alaska | US | 115 | 90 |
| Los Angeles , California | US | 100 | 1 |
| Denver , Colorado | US | 1609 | 50 |
| Washington, DC | US | 7th | 5 |
| Chicago , Illinois | US | 179 | 40 |
| Boston , Massachusetts | US | 43 | 23 |
| New York City , New York | US | 10 | 22nd |
| Oklahoma City , Oklahoma | US | 396 | 3 |
| Nashville , Tennessee | US | 182 | 12 |
| Dallas , Texas | US | 128 | 7th |
| Salt Lake City , Utah | US | 1288 | 53 |
| Seattle , Washington | US | 54 | 8th |
- Measurement data only partially comparable:
- Canada: 2 cm snow cover 25.12. 7:00 am, dates 1955-2011
- USA: 1 inch (2.5 cm) snow cover December 25th. 7:00, data 1988-2005
Southern hemisphere
In the southern hemisphere of the earth, December is midsummer . In addition, there are hardly any land masses outside the tropics in the southern hemisphere - apart from the Antarctic continent . Therefore, white Christmases are usually a special exception there.
- There are glaciers on the South Island of New Zealand , in the high alpine areas of the New Zealand Alps , summer snowfall is about as frequent as in the Alpine region (every few years).
- Snowfall also occurs in Tasmania and Victoria : for example 2006, the coldest Christmas day in Victoria for 150 years, in Hobart for 2 decades; Snow in Thredbo , on Mount Baw Baw and elsewhere. In 2010 there was snow on December 20th.
Individual evidence
-
↑ a b c d ZAMG : Statistics on the topic of white Christmas , December 4, 2013, News (together with fresh snow in Austria, hurricane in Northern Europe ).
Every year: “White Christmas?” , Vorarlberg online, vol.at, December 13, 2011 (quoted by Alexander Orlik, ZAMG) - ↑ a b c d White Christmas ( Memento from June 28, 2013 in the web archive archive.today ), MeteoSwiss , last change December 13, 2012.
- ↑ Claudia Salbert: Statistics on White Christmas: What do we understand by White Christmas? ( Memento of October 14, 2013 in the Internet Archive ). In: wetter24.de , December 7, 2011.
- ↑ a b c d Where is it white in Germany at Christmas? , wetterspiegel.de, November 30, 2012. Accessed December 19, 2016.
- ↑ a b Are you dreaming of a white Christmas? In: National Climatic Data Center . National Oceanic and Atmospheric Administration , accessed December 19, 2016 (American English).
- ↑ a b Chances vary for a white Christmas. (No longer available online.) In: CBC News. December 24, 2010, archived from the original on May 30, 2013 ; Retrieved December 25, 2010 (Canadian English).
- ↑ See also “ Perfect Christmas: a white Christmas morning and snow in the air on Christmas day, ie, a measurable snowfall on Christmas ”. Chance of White Christmas : Definitions , Environment Canada , December 11, 2012.
- ↑ Weather Christmas - is there a white Christmas? In: www.wetterprognose-wetter Prognose.de. Retrieved November 4, 2016 .
- ↑ White Christmas. Federal Office for Meteorology and Climatology , December 5, 2016, accessed on June 21, 2017 .
-
↑ a b Will it be a white Christmas? : What is a white Christmas? , metoffice.gov.uk, December 7, 2012 (English);
Data there (text & more detailed table): in 52 years “ snow on the ground ”: 23 ×, “ widespread covering of snow (where more than 40% of stations in the UK reported snow on the ground at 9am) ” 4 ×, “ Snowfall ”: 29 ×, “ a snowflake has fallen ” 38 × in 62 years - ↑ So Mozart writes a song Come Dear May and make the trees green again ; accordingly, this suggests a beginning of winter September / October if one considers the phenology that prevails in the far north today
- ↑ see for example Hans-Rudolf Mengers: White Christmas was always the exception , Rüstringer Heimatbund, accessed December 19, 2016.
- ^ Martine Rebetez: Public expectation as an element of human perception of climate change . In: Climatic Change . tape 32 , no. 4 , April 1996, ISSN 0165-0009 , 2.1 Hypotheses to explay the origins of the White Christmas image, p. 498–501 , doi : 10.1007 / BF00140358 ( slf.ch - Martine Rebetez [PDF; accessed December 25, 2014]).
- ^ Christiane Vielhaber: The dream of a white Christmas. In: Kölner Stadt-Anzeiger. December 23, 2013, accessed December 25, 2014 .
- ↑ The Christmas carol Silent Night, Holy Night of the Baroque still speaks of the Holy Land itself.
- ↑ "Real winter cold and snow domination have become almost unknown in the Christian month for several years. No Christmas poem that speaks of cold, snow and ice wanted to fit anymore. Did I hear someone say, 'Today Christmas is celebrated outdoors; in the garden outside the tree has to burn, and there we sing our songs and recite the poems. '”From N. Arnet: Overview of the weather in the four years 1911 to 1914. Adapted from the observations of the Meteorological Station in Lucerne. Separately printed from the communications of the Lucerne Natural Research Society. VII volume, 1915 (?). Quoted from White Christmas ( Memento from June 28, 2013 in the web archive archive.today ), meteoschweiz.
- ↑ Incidentally, the text is perhaps characterized by artistic freedom, the sentences about snowfall and strict forest (“the lake is still and rigid”) contradict each other, unless a warmer break in a cold phase with more snow is expressly described.
- ↑ a b White Christmass are relatively rare. ZAMG Climate News. December 16, 2015 - data for the provincial capitals according to the measurement series 1951–82 and 1983–2014 (63 years); shows a halving of the events for the second interval.
- ↑ Nick Wiltgen: What Was the Deepest Snow in Your State? In: weather.com . March 9, 2015, accessed December 19, 2016.
- ↑ Why at Christmas? ( Memento from July 6, 2016 in the archive.today web archive ). at.wetter.tv weather blog, December 18, 2012.
- ^ R. Seager, et al .: Is the Golf Stream Responsible for Europe's Mild Winters? In: Quarterly Journal of the Royal Meteorological Society 128, 2002, pp. 2563-2586
- ↑ a b c on the influence of the correlations between westerly wind drift with the Azores high and Gulf Stream or Aleut low and Japan Current on the winter climate, see Stephen C. Riser, M. Suzan Lozier: News from the Gulf Stream . In: Spectrum of Science , May 2013, rubric Earth and Environment; Climate research , pp. 66–73 ( article online , Spektrum.de, limited).
- ↑ a b Even in the inner-Alpine region only in 50%; Evaluation of the years since 1991; closed snow cover on December 24th or 25th; see ZAMG: Statistical information on the topic of white Christmas , December 4, 2013.
- ↑ Thus, for Germany, 98% is given for Lindau on Lake Constance, 35% for the near Bregenz: the values for Austria are therefore to be considered significantly higher in comparison.
- ↑ Snowfall in Ireland ( Memento of January 21, 2013 in the Internet Archive ), Met Éireann (PDF; 1.0 MB; English).
- ↑ Nader verklaard: Witte kerst door de jaren heen ( Memento of 15 August 2015, Internet Archive ). Koninklijk Nederlands Meteorologische Instituut , December 27, 2012 (event 9 times in 110 years; Dutch).
- ↑ Normal frekvens för vita jular 1931–1980 , distribution map , Sveriges meteorologiska och hydrologiska institut , October 26, 2009, updated April 23, 2014, accessed March 20, 2016 (Swedish).
- ↑ Richard Kerbaj: Amid the embers, no one dreamed of a white Christmas ( Memento from December 6, 2016 in the web archive archive.today ). In: The Australian , December 26, 2006.
- ↑ A white Christmas, in Australia? , Blog entry in leefe.ratestheworld.com.au, December 26, 2006 - with links to reports.
- ↑ Parts of Australia may face white Christmas with summer snow . In: The National online, December 20, 2010, accessed December 19, 2016.