When considering cold nights and arctic conditions, many places come to mind. Finland, Sweden, Norway. Siberia, Canada. Maybe even the USA, with some high-altitude locations and snow cover. Greenland, obviously Antarctica. But Switzerland?
Yes – and not only Switzerland. The inner Alpine regions can be frigid in winter. Last night is such an example. Although brief, it was intense: at least 20 locations recorded a temperature below -20 degrees Celsius. Not cold enough? The coldest was Sägistalsee at -40.3C, before the station went “blank”. According to the station’s owner, it is unlikely that a much lower temperature would have been recorded if the station hadn’t lost connection.
What is so special about Sägistalsee
Sägistalsee is located in the Swiss canton of Bern, at an altitude of 1937m. This is in part an explanation itself: dry air has the ability to lose its heat at a very rapid pace.
The second part of the explanation is a solid snow cover. Snow has a double function in exacerbating cooling: it insulates the air from the heat in the ground, and due to its larger albedo also radiates more heat into space.
However, this is only part of the explanation. The other explanation is a phenomenon that’s called “Kaltluftsee” in German, or “cold air lake” as literally translated in English. These places are often found in mountains and occur next to north-facing slopes where air starts to cool down and sinks into a valley, without mixing with the other air. The result is an inversion, underneath which there is hardly any moist left. This again exacerbates the cooling.
With the mountain slopes to the south, there is no direct sunshine in the winter period to break the inversion. The cold air can persist, until there is more movement in the atmosphere that forces the mixture of air.
Such too is the case of the Sägistalsee, which happens to be an actual lake, where mountains are located around the lake. WIth roughly 2500 meters, the altitude is limited, but the valley is ideally located to make a cold pool of air: mountains on 3 sides and a small uphill slope when leaving the valley.
So is it special? Considering the coldest temperature in Switzerland ever recorded is -41.8…Quite special!