When is the earliest date for the first measurable snowfall in some large cities in the lowlands and in the deep Alpine valleys? When does the first snow fall on average? And how does it look like this year and in the future? Find out more below.
How and when are measurements taken?
Before discussing the earliest and average date of the first measurable snowfall, a few explanations on how and when measurements are taken. MeteoSwiss measures the new snowfall in centimeters and the total snow depth in the morning at 6 UTC, i.e. at 8 a.m. during summer time and at 7 a.m. Swiss time during winter time. A day with a snow cover only appears in the statistics if there is at least 1 centimeter of snow at 6 a.m. UTC. Occasionally there is a case where a blanket of snow forms, which then melts again in the morning or there is only a small patch of snow that cannot be measured. So it may well be that it was white once, but the day does not appear as a snow day in the weather annals.
Earliest date: Usually October
Table 1 shows the date of the earliest measurable snowfall (at least 1 centimeter) for some large cities in the lowlands and deep Alpine valleys since measurements began. It can be seen that the date varies from the beginning of September in Chur to the beginning of November in Geneva and Lugano. In most places, the earliest snow day is in October (see also Fig. 1).
Table 1: Earliest date of first snowfall (at least 1 centimeter of snow with morning measurement at 6 a.m. UTC)
Fig. 1: First snowfall at the end of October 2018 in Sargans; Source: Roger Perret
Average date: Mostly first half of December
Table 2 shows the average date for the first measurable snowfall since 2001, which is usually in the first half of December. In St. Gallen, which is at slightly higher altitude, the first snowfall occurs on average on November 11 and in Chur on November 25, whereas in Geneva it does not occur until December 17 and in Lugano on December 25. Occasionally, there have also been winters with no snow at all, such as in the winter of 2019/2020 in Basel, Bern and Zurich. On the other hand, it has also happened that a lot of snow fell in the second half of November (see Fig. 2).
Table 2: Average date of the first snowfall
Fig. 2: At the end of November, there can be a "Chlapf" of snow, for example in Sargans in 2021; Source: Roger Perret
And this year?
At the stations under consideration, it briefly turned white in Bern on the Sunday before last (November 12) with a warm front (see Fig. 3), but the snow quickly melted again and it was already green again on Monday morning at the time of the snow measurement.
Fig. 3: On November 12, it was already white in Bern at short notice; Source: roundshot
Next weekend will be exciting in terms of the first snow: With a low pressure system over north-eastern Europe, increasingly colder air will flow in on Friday with a north-westerly current, causing the snow line to drop to low altitudes on Saturday night. It will remain there over the weekend and at the beginning of the week. However, there will only be occasional wet snow showers in the lowlands, which are unlikely to be heavy (see Fig. 4).
Fig. 4: Expected amount of fresh snow from Saturday morning to Sunday morning; Source: MeteoNews, UBIMET
The situation is different in the northern Alpine valleys, where snow and even a thick blanket of snow can be expected again and again with northern accumulation. This applies in particular to St. Gallen and Chur at the stations under consideration, while there is unlikely to be any measurable fresh snow at the other stations in the north, although it may become a little white in places. There will certainly be no snow (or precipitation) in southern Ticino, which is protected from the humid air masses.
There is no sign of stabilization or major moderation in the coming week either, and the situation from the weekend is likely to repeat itself in the second half of the week. So it remains exciting in terms of snow, MeteoNews will keep you up to date in any case.
And in the future?
Due to the steadily rising temperatures as a result of climate change, snow is falling less and less frequently in the lowlands, which means that the date of the average first snowfall is likely to be pushed back. The fact that there is less and less snow in the lowlands in winter can also be seen from the fact that there are fewer and fewer white Christmases compared to the past. This trend is very likely to continue in the future.
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