Where the winter sun shines in Switzerland

Winter sun varies far more than summer sun

The winter sunshine indicator measures the share of the possible hours of sunshine that a municipality actually receives in the cold season. Fog, low cloud and hills on the horizon all cut it, so the figure reflects local geography as much as weather. Locarno receives 59% of the possible hours and is ranked 3 of 1,806 municipalities. At the other end of the scale, Kreuzlingen, on the lake shore in the north-east, receives only 20%.

Between those two lie the big cities. Geneva, Bern and Basel each receive 29%, while Zürich receives 25%. In the north-east the figures drop again: Winterthur receives 23% and Frauenfeld receives 21%.

The main cause is fog. In cold, still weather a layer of low cloud settles over the plateau and the lake basins for days, while the slopes above it stay bright. The weakest winter values cluster on the plateau, and because the series uses whole percentage points, many neighbouring municipalities tie there.

In summer the map is almost flat

Summer changes the picture. The median municipality receives 51% of the possible hours, and the big northern cities sit close to that figure: Zürich receives 51%, Bern receives 53%, Basel receives 53% and Kreuzlingen on the lake receives 50%. The fog belt that cost them so much sun in winter is gone.

A few places stand out in summer for the opposite reason. Geneva receives 60% and Sion receives 61%. In the Rhône valley rain is scarce: Sion gets 613 mm of precipitation a year, against a median of 1,117 mm. Grimisuat tops the national summer table with 64%.

Cloud and rain pull the other way in central Switzerland. Engelberg receives 41% of the possible hours in summer, the lowest share of any municipality, and it gets 1,836 mm of precipitation a year. It lies in Obwalden, where the mountains gather cloud over the valley floor.

In the Alps the seasons swap places

Mountain resorts break the pattern. Zermatt receives 56% of the possible hours in winter and 53% in summer. Davos receives 52% in winter and 48% in summer. For St. Moritz the shares are 55% and 50%, and for Pontresina they are 56% and 47%. In all four, winter is the brighter season.

Altitude explains it. Above the fog layer, winter days are clear and dry, while in summer afternoon cloud builds over the peaks and cuts the hours of direct sun. The reversal reaches the northern valleys too: Engelberg receives 47% in winter and 41% in summer, and Grindelwald receives 48% and 46%.

Bright does not mean mild. Zermatt has the lowest January average of any municipality, −9.8 °C. The lowlands sit near freezing instead: Kreuzlingen and Zürich average 0.9 °C and 1.0 °C in January, yet they receive only 20% and 25% of the possible hours of winter sun.

A bright south and dry inner valleys

Over a whole year, two groups of municipalities dominate the sunshine table: those on the southern side of the Alps and those in the dry inner valleys of Valais. Grimisuat comes first with 58% of the possible hours, and Muralto follows with 57%. In the same group, Sion and Locarno each receive 57%, against a median of 42% across municipalities.

The southern advantage does not stop at the cantonal border. Poschiavo and Brusio, in the Italian-speaking valleys of Grisons, receive 59% of the possible winter hours, as do Locarno and Arbedo-Castione in Ticino.

Sunshine and warmth do not travel together. In January Locarno averages 1.9 °C, while Poschiavo averages −6.1 °C, a gap that altitude explains. The sunshine share measures clouds and horizons, not temperature.

How to read these shares

A relative sunshine share compares the hours of sun a municipality receives with the hours it would receive under a cloudless sky. It is a ratio, not a count of hours, so it says nothing about the length of the days. Deep valleys can lose hours to cloud and to the surrounding mountains.

Each municipality has a single figure, so large municipalities that span a valley floor and a mountainside hide differences within their borders. The values are long-term averages for 1991-2020, and they say nothing about a particular winter. A cold, clear month and a grey, mild one can appear in the same average.

The annual table is reported with one decimal, so ties are much rarer there than in the seasonal tables. That is why the annual ranking can point to a single municipality at the top, while the seasonal tables show groups of municipalities with identical shares.

Warming does not follow the sun

The same climate data show how much the annual average temperature has risen compared with the earlier reference period. Rheinfelden shows the largest rise, 2.0 °C, and the municipalities just behind it are also in the north-west. At the other end, La Tour-de-Peilz and Grimisuat each show a rise of only 0.7 °C.

Grimisuat is a telling case. It shares the smallest rise in the country with La Tour-de-Peilz, and it also ranks first for annual sunshine. A clear sky and a modest rise go together there, but the pattern is local and should not be generalised.