December so far has been far too wet, snowy on the mountains and too cloudy. Temperatures are also around the norm. The half-time balance.
The first half of December was characterized by frequent disturbances with repeated precipitation. In particular, there was a lot of precipitation throughout Switzerland at the beginning of the month and in the north on December 11 and 12, which led to a tense flood situation in some places. Overall, the precipitation deviation so far in December across the whole of Switzerland is more than 200%, i.e. three times as much precipitation fell as normal (see Fig. 1). The positive deviation is smallest on the northern edge and in Ticino.
Fig. 1: Precipitation deviation so far in December compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
If you compare the total precipitation that has fallen so far with the average total for the whole of December, there are stations where more than twice the normal December precipitation has already fallen.
Fig. 2: Highest precipitation totals so far in December; Source: MeteoNews, UBIMET
Far above-average snowfall in the mountains
After there was widespread snow and a real winter wonderland in the German-speaking part of Switzerland at the beginning of the month, the snow increasingly melted away again with the thaw in the lowlands, and at the beginning of this week the snow line was even above 2000 meters in places. At high altitudes, however, snow fell continuously, resulting in a lot of fresh snow. As a result, the snow depth is currently well above average compared to the long-term average, especially at around 1500 meters in the north (see Figs. 3 and 4).
Fig. 3: Current snow depth compared to the long-term average (the darker blue, the higher than average); Source: WSL-Institut für Schnee-und Lawinenforschung SLF
Fig. 4: Currently snow-covered Valais Alps (La Vuardette 2,150 m); Source: roundshot
On the Säntis, for example, the snow depth of 340 cm is currently higher than it has ever been at this time of year (see Fig. 5).
Fig. 5: Current snow depth on the Säntis and long-term comparison; Source: myweather.ch
About normal temperature
After a cold start with a widespread icy day on December 3 (maximums below 0 degrees), there was a thaw from December 5, and at the beginning of this week the maximums were in the double-digit range in many places, which is very mild for the time of year (see Fig. 6).
Fig. 6: Course of maximum temperatures so far in December at Zurich Airport; Source: MeteoNews
Across Switzerland as a whole, the temperatures so far in December are pretty much in line with the norm (see Fig. 7), with a surplus of around 0.5 to around 2 degrees in the lowlands and a deficit of 0.5 to over 1 degree in the mountains. The reason for this is the virtual absence of fog or high fog and the generally good mixing of the air.
Fig. 7: Temperature deviation so far in December compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
Far too little sun
So far in December, the sun has shone significantly less frequently than the long-term average, with a negative deviation of almost 50% across Switzerland (see Fig. 8). On the Chasseral, there has been less than one hour of sunshine so far, making the deviation 98%! Only Stabio recorded a small surplus of sunshine.
Fig. 8: Deviation in sunshine duration so far in December compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
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