December can hardly please anyone: It is true that there was snow in large parts of Germany this year. But in view of the energy crisis, one could have done without the sometimes bone-chilling cold with double-digit minus degrees. At the beginning of this week it suddenly got warmer that the rain on the frozen ground from the northwest produced bad black ice in many places. And just in time for Christmas Eve, when for many a white blanket of snow is part of the ideal image of Christmas, which is not lacking in idealization, as of Monday rain and very mild, windy weather with double-digit maximum temperatures is forecast almost everywhere in Germany, which, according to the German Weather Service (DWD ) should only survive in higher or very sheltered locations.
But this is just a return to normality. The weather conditions over the past few weeks have been unusual. Because the reason for the cold was a so-called blocking weather situation, in which a high pressure area – rotating clockwise as always in the northern hemisphere – developed over Iceland and a counter-rotating low pressure area over the Azores, so that the usual mild westerly current over Central Europe was interrupted. Now this situation is reversed, and warm, humid air from the Atlantic is streaming in, just in time for the holidays.
In fact, this pattern is typical, the DWD even has a technical term for it: “Christmas thaw” is the name of the phenomenon. It belongs to the so-called singularities like the sheep cold in mid-June and the Indian summer at the end of September: not every year, but quite often with six to seven out of ten years, the weather at the end of December is relatively mild, which is not conducive to a Christmas snow cover.
“Thaw” implies that there is something to thaw
However, the term should be viewed with caution. On the one hand, the effect is not particularly pronounced. It was like this according to a DWD evaluation in Frankfurt, for example, on average between 1949 and 2017 around Christmas around half a degree warmer than in the middle and end of December, but still significantly colder than at the beginning of December, with considerable fluctuations.
The prospects for snowmen are bleak – but at least there are some this December.
(Photo: imago stock&people/imago/Norbert Schmidt)
Also, “thaw” implies that something is there to thaw – and that is becoming less and less the case. December is the warmest winter month anyway, astronomically winter only begins with the winter solstice on December 21st. According to this, Christmas is actually a month too early in terms of snow. Although the sun is lowest in the northern hemisphere shortly before Christmas, the cooling of the atmosphere is lagging behind by several weeks due to the inertia of the oceans in particular, so that the chances of cold and snow at the end of January are significantly better.
And climate change isn’t making things any better. According to a DWD analysis the probability of snow cover on December 24, 25 and 26, at least in the southeast of Baden-Württemberg and Bavaria and around the low mountain ranges from 1961 to 1990, was still more than 30 percent. From 1991 to 2020, the average was 13 percentage points less. In Munich, for example, one of the best places for Christmas snow in the lowlands, in the past few decades it has only worked every seventh year instead of every third year as in the previous period – and the trend is falling.