Why is the Swiss sky grey for weeks?
Because of Hochnebel, a flat layer of low cloud that often sits over the Swiss lowlands from October to February, for days or weeks. In calm weather its top is usually around 800 metres, according to MeteoSwiss, and above it the sun often shines. The way out of the grey is up.
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The real rule
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From October to February, a flat layer of low cloud, the Hochnebel, often sits over the Swiss lowlands for days or weeks, while the mountains above are in full sun. In calm weather its top is usually around 800 metres, so a short train or cable-car ride up can take you out of the grey. Locals check the forecast for the fog's upper limit and go up at the weekend. If the grey months weigh on you, you are not alone: plan sun trips, keep moving, and talk to your GP if it lasts.
Blüemli's verdict: Ding. Sun above the lid. In calm weather the top of the fog is usually around 800 m. Above it, the sun often shines.
HOCHNEBEL: literally: “high fog”; really: the grey lid over the lowlands in autumn and winter Ueli's Word
Be like Ueli. When the lid stays shut, go up.
Learn more: Zurich, Geneva or Basel?
The rule, explained
MeteoSwiss explains the grey in a blog post of 3 February 2025 on how the upper limit of the Hochnebel behaves. Hochnebel forms in stable high pressure, which is typical for the cold season. When the pressure is balanced and there is no wind, the upper limit of the Hochnebel usually lies around 800 metres. With Bise, the top lies higher. And to escape the fog grey, as MeteoSwiss puts it, the only way was up. That is why locals check the forecast for the fog's upper limit before the weekend, and why a short train or cable-car ride can change the day. Ueli's version: the nine o'clock train, three hours of sun and tea from the thermos, then back down into the grey.
Sources: MeteoSwiss blog, Wie verhält sich die Obergrenze des Hochnebels?, 3 February 2025
Questions people ask
How high does the Swiss Hochnebel reach?
In calm weather its upper limit usually lies around 800 metres; with Bise it lies higher (MeteoSwiss).
When is Hochnebel season in Switzerland?
Often from October to February. It forms in stable high pressure, which MeteoSwiss calls typical for the cold season (MeteoSwiss blog).