A high-altitude low over France in the second half of July 2025 was responsible for the fact that there was no real summer feeling in large parts of Switzerland. The south and Valais were most likely to benefit, while frequent precipitation on the northern slopes of the Alps certainly caused the odd barbecue party to fall through.
While many large-scale weather conditions in Switzerland allow for relatively accurate forecasts, this seems to be difficult for the meteorological institutes in the case of an altitude low. For hikers and mountaineers, it was difficult to make a clear statement about the weather forecast for mountain tours from the wide range of forecasts: five different weather reports resulted in five different tendencies - you could choose the forecast you wanted, so to speak.
But how exactly does such an altitude low actually work? The air coming in from the southwest, from France, was warm and humid. Because it was unstable and stratified, it often led to the formation of cumulus clouds - with showers and thunderstorms, especially in the afternoon and evening. The Alps acted as a lift, causing the air to rain down. This resulted in accumulated precipitation. Later, the low pressure core moved southeast towards the Gulf of Genoa. This resulted in a northern dust situation, with heavy precipitation on the northern side of the Alps, whereas the southern side of the Alps and Valais were largely spared.
But as the saying goes, rain is followed by sunshine - and the general weather situation looks promising for August: stable and therefore ideal for hikes and mountain tours, provided temperatures don't rise too much and don't put even more strain on our glaciers than they already are.
