Every Christmas the same question arises: will there be snow in time? This December it remains unanswered for an unusually long time – shortly before Christmas Eve, the weather situation is still very uncertain.
However, anyone who thinks that sledding weather was guaranteed earlier on the holidays is wrong. It is a well-known phenomenon for people to glorify the weather of the past. In fact, a white Christmas in Germany used to be the exception rather than the rule in large areas. According to one, the reference period from 1961 to 1990 current analysis of the German Weather Service (DWD) the probability of a snow cover from December 24th to 26th only in the low mountain ranges and in the Alpine region is more than 50 percent. Even then, in the lower elevations, there was no more than a white Christmas every two to three years. Even less common in the northern half of the country.
However, climate change has meanwhile further worsened the chances of snow being presented. If you compare the period from 1991 to 2020 with the thirty years before, the probability of a white Christmas across Germany has fallen by an average of 13 percentage points, according to DWD data. Regionally, it is sometimes significantly more: Munich, for example, used to be under a blanket of snow at Christmas around every three years, but now it only works around every seventh year.
Cold air comes from the north, warm air from the south
And this year? A few days before Christmas nothing is decided. DWD meteorologist Adrian Leyser sees a lot of excitement; An interesting but uncomfortable situation for weather experts, after all, one expects clear forecasts from them – but that is currently difficult. “We have a borderline weather situation: Scandinavian cold air comes from the north, warm air from the south,” says Leyser. On Christmas Eve, the air masses could collide over Germany, then it could snow heavily on the cold, i.e. the north side of the front. To the south of it you should expect rain and sometimes black ice. “The border should tend to be in the north or northeast, but where exactly is still very uncertain,” says Leyser.
It is even more difficult to predict what will happen after the holidays with winter – long-term forecasts are notoriously unreliable despite all the advances in forecasting. However, there are fluctuations in the air pressure conditions over the Atlantic, which can at least favor certain developments. In winter, this includes the so-called North Atlantic Oscillation. Put simply, it fluctuates between two extreme positions: In the strongly positive phase, there is a strong Icelandic low over Iceland, and a pronounced Azores high over the Azores. The two systems mesh like gears and forcefully pump air from the west to northern Europe, so that the usual westerly current is even stronger, resulting in mild, rather humid winters.
In the strongly negative phase, the pressure difference between Iceland and the Azores is much smaller. This leads to the circulation being blocked, the usual westerly wind drift stalling and the high-altitude wind band, the jet stream, making waves. In such a situation, very cold air from the north or northeast can slosh into Germany. For example, it was in December 2010, when there was a lot of snow, when new record snow depths were measured in many places in Germany.
In fact, the North Atlantic Oscillation is currently in the negative phase. “At the turn of the year it could drop again significantly after an increase,” says Leyser. “The consequences for our weather are unclear.” That’s because there are many other influencing factors. Depending on where the high and low pressure areas are located or how widespread snow is, the weather in Germany can be one way or the other.