White Christmas (weather)

White Christmas is the weather phenomenon that Christmas snow falls or lies.

The concept: Meteorological and cultural concepts

By " white " Christmas is generally understood that on Christmas Eve (24 December), Christmas Day (25 December) and Boxing Day on (26 December ) or at least at some point falls in this time either snow or snow.

The idea of a white Christmas is closely associated with Christmas carols like Oh Tannenbaum ("... even in the winter when it snows ...") or Softly Falls the Snow connected, and has led from Europe starting to become a world prototypical idea of ​​how the Christmas holidays should look like. In the historical birth of Jesus of Nazareth in Palestine, who are commemorated at Christmas, there was no snow with high probability.

Each year, the forecast about the snow conditions to Christmas theme of weather forecasts. Taken Meteorological mean white Christmas that snow cover is to be found, which is generally at least 1-2 means cm of snow, and they do not wegapert over the holidays, or that the precipitation as snow takes place ( snow day ), and it's cold enough that this also remains lying ( or at least air - soil temperature at 0 ° C). If there is only a broken snow cover or the snow is only temporarily - that is a " Schneedeckentag " ( meteorologically at the closing date in the morning when it is coldest in the days running, at other times is not measured, but also patchy snow cover and less than 1 cm recorded ) - or is one of the days at least a Schneefalltag (occurrence of snow sometime during the day), the Christmas holidays are only halfway, " white ", otherwise more "green", as they say.

To do spot the frost line (0 - degree mark ), but at least the snow line (falling snow melts not to rain, about 4 ° C) are deep enough and stay deep enough. This is snow, the weather this Christmas season or even the Vorweihnachtstage ( later Advent ) must be for it have been favorable: If the snow conditions well before Christmas, even a short period of warm weather this can not resolve. This snow is falling, the weather must be suitable directly for Christmas.

Therefore, the probability of a white Christmas is dependent both on the weather situation, the weather, the Christmas holidays, as well as by the local weather and the altitude or other cofactors of precipitation, such as the wind conditions. Another favorable circumstances would be like a snow -less intense winter, which can freeze the ground well, followed by extensive snowfall, then a pre-Christmas high-pressure phase with cold, solidified by sunshine, the ceiling, or by repeated rain / frost periods. "Really perfect white Christmas" would, " where it snows on the 24th so that the snow still lying on the 25 remains ," or " snow on all three days of Christmas ".

The problem is the prognosis in addition to the general prediction of the weather conditions, which is today through computational models quite reliably, precisely by the front-end systems the weather changes (ie relative chaotic conditions ), which are the most difficult to calculate on time and intensity in arrival at a particular location. In addition, the determination of the zero level is particularly locally imprecise. The combination of the effective date and the thermal limit of the freezing point makes predicting a white Christmas to one of the complex problems of meteorology. Excluded are stable cold high altitudes with already existing, snow, as is typical for continental positions, there is the question of white Christmas relatively marginal.

The expectations of a white Christmas are regional differences: while one would expect quite extensive in the Alps snow (1 cm of snow is " dusted ", but no real " snow " in the normal local understanding ), it is customary in England with its mild winter climate to bet about, whether in the 24 hours of December 25, at least a snowflake presents in one place. Also, the date is dependent on regional customs. In some regions, the main celebration time of the afternoon of Christmas Eve with the Christmas Vespers, elsewhere the time between dinner and presents on Christmas mass at midnight, in other regions of the Christmas Day itself ( 25 December).

Historically, likely in the middle modern times ( 17-18 century, Baroque) white Christmas have been the rule; this interglacial phase is called the Little Ice Age, and the idea of cold, snowy Christmas was not worth mentioning yet pleasing. Only after the end of the late 19th century ( Romantic ) seems to have become the subject to date ( the Biedermeier was still overshadowed by severe winters after the volcanic eruption of Mount Tambora in 1815 ). Thus, from weather records of wennde 19-20. Century shows that you were surprised about the increasingly mild December. During this time, Christmas carols with explicit reference arise as snow falls softly snow ( Ebel 1895). Also in nativity scenes not in the Holy Land itself, but the snow- Central Europe is presented during the 19th century increasingly similar in the snowy tree Christmas decorations with tinsel. In the 1940s, one already defined then the Christmas warm spell as a Central European singularity (regular feature ) of the reversing early winter / mid-winter, at the time the failure of the White Christmas was already common. Ever since the song White Christmas ( I. Berlin 1947), probably the best-selling single of all time, the idea of ​​the snow-covered Christmas feast is valid worldwide. The further progression of global warming during the 20-21. Century white Christmas today in much of the temperate latitudes the exception, not the rule.

Regional

Europe

Would Before Christmas temperatures around the freezing point and reign as northern to north-west winds, which seep from the polar regions, humid cold air masses that if they mix from the west with damp mild air from the Atlantic, leading to snow. Follows a cold east or northeast side, the snow stays. In Central Europe today is the singularity of the Christmas thaw the rule as it goes back to the model of Schmauß from the 1920s and was defined by Flohn in the 1940s. This is a regular burglary milder Atlantic air masses ( Atlantic Deep ) mostly west - southwesterly direction, although in previous cold ( about a stable Russia high ) can guarantee snow, by abnormal heat but consistently leads to thaw, and make a white Christmas naught. This weather pattern is controlled by Iceland low and the Azores high, two other important centers of action of the European weather patterns. If they dominate the high Russia, Christmas thaw is likely. Be greatly influenced the Atlantic lows by the Gulf Stream, the "heat pump in Europe".

In the 2000s the probability of a white Christmas is for the lowlands of central Europe at around 20 to 30%, so only two or three times per decade. Snowfall is much rarer than snow cover.

North America

The climate of North America is characterized by the lack of an east-west barrier, but the pronounced climatic divide of the Cordillera, which forecloses almost the entire continent of the West Wind Drift. Therefore, cold polar air southward flow freely, and both from the northwest (controlled by the Aleutian ) and from the south from the Caribbean wander a wet front systems over the land mass, while the interior is dominated by the drought in Lee. The Hudson Bay as "America's icebox " but reach deep into the interior, the Great Lakes there act as a climatic divide. On the Atlantic coast of the cold Labrador Current, the precipitate - to-temperature gradient returns to the meeting with the warm Gulf Stream ago to North Carolina, so the north are drier than the south. The Azores high as " weather engine " of the North Atlantic - even in winter - may relocate to North America quite close. This leads to the extreme bettors in North America, and there are several large-scale weather scenarios for a white Christmas in question, from the Nor'easter on Blizzard's up to running onto stable cold air Caribbean lows. The West Coast, however, is dominated strictly oceanic, and move the temperatures almost 20 ° to the North: Alaska's south and west coasts (latitudes such as Scandinavia ) has about the same ratios as Newfoundland (latitudes such as central Europe). Here Aleutian and Japan Current / North Pacific current control the winter air, the smuggle the heat similar to Europe far to the north.

The probability of a white Christmas ranges from less than 10% for the entire southern half of the U.S. and the entire west coast to Alaska almost up to about 90 % west of the Great Lakes and New England. Sure White are just the permafrost regions of the far north of Canada.

Southern Hemisphere

In the Southern Hemisphere of the Earth is in December midsummer. In addition, there are in the southern hemisphere - except for the Antarctic continent - hardly landmasses outside the tropics. Therefore, a white Christmas there are usually a special exception.

• Glaciers there are in the South Island of New Zealand, in the high alpine regions of the Southern Alps is summer snow about as common as in the Alpine region ( every few years).
• Snowfall occurs in Tasmania and Victoria: So around 2006, the coldest Christmas Day in Victoria for 150 years, in Hobart for 2 decades; Snow in Thredbo, Mount Baw Baw and elsewhere. 2010, there was snow at 20.12.