Boelo: 138 km/h on the Säntis is no benchmark for the lowlands
MeteoSwiss explains the strong regional differences of Sunday's storm. In Basel, parts of the fair were temporarily closed; no nationwide damage assessment is available in the sources reviewed.
The storm depression «Boelo» swept across parts of Switzerland with strong to gale-force gusts on Sunday, 25 October 2026. The review published by MeteoSwiss on Monday cites 138 kilometres per hour on the Säntis. In the lowlands of German-speaking Switzerland, peaks mostly ranged between 60 and 80 kilometres per hour.
That difference is decisive for how the event is classified. A summit measurement does not describe the load on residential areas. Nor does a precautionary closure prove that damage occurred. What is confirmed are pronounced regional differences and temporary restrictions at the Basel Autumn Fair. A Switzerland-wide total of damage or deployments cannot be derived from the publications reviewed here.
Why the wind did not arrive everywhere at the same time
«Boelo» passed north of Switzerland: its core moved north of Ireland and Scotland on Saturday and reached the Norwegian coast on Sunday. Switzerland lay within the influence of its frontal system. Between the warm and cold fronts, strong air flowed in from the south-west to west.
Mountains, the northern Jura foothills and slightly elevated locations were particularly exposed at first. MeteoSwiss cites gust peaks in the range of 90 to 110 kilometres per hour for sites such as Rünenberg and Lägern. But a measurement at such a location is no substitute for the value at the nearest valley floor.
According to the Federal Office's analysis, a rather stable layering of the air, supported by intermittent precipitation, made it harder for the strong high-altitude wind to mix down. With the cold front, the wind also reached lower elevations in places. Behind it, the weather calmed quickly. A quiet morning at one location could therefore not be taken as an all-clear for the whole day.
An unusual foehn at the same time as a westerly wind
In the Alps, a special foehn phase came on top. Foehn is usually associated with a southerly high-altitude flow and precipitation south of the Alps. On Sunday, by contrast, the flow aloft was westerly to north-westerly; rain also fell on the northern side of the Alps.
Nevertheless, a pressure surplus of just under nine hectopascals existed in the south at times. It was able to drive cold air northwards across the Alpine ridge. MeteoSwiss calls this constellation a shallow counter-current foehn, or «Güllerföhn». For a short time it reached Lake Constance. According to the Federal Office, however, the strongest gusts measured in Switzerland came from the storm field, not from this foehn phase.
On the northern Alpine slope, according to MeteoSwiss, precipitation amounts of around 20 millimetres also accumulated. This local order of magnitude, too, is not a Switzerland-wide rainfall figure.
What Basel closed – and reopened
At the Autumn Fair on Sunday, Petersplatz, the Rosentalanlage and the Baumhain on Münsterplatz stayed closed because of possible falling branches. Other areas remained accessible. The official event page later added explicitly that from 18:00 the affected squares were open again.
The measure can therefore be described neither as an all-day closure of the entire fair nor as proof that branches actually fell. Precaution is taken precisely before it is established whether damage will occur. An assessment of whether the trade-off was appropriate would have to take into account local wind conditions, the tree stock and the forecasts available at the time of the decision.
Read peak value, forecast and damage separately
SRF Meteo had expected gusts of up to 150 kilometres per hour locally in the mountains in advance, and 50 to 80 in the lowlands. Such forecast ranges are not to be equated with station maxima measured afterwards. Values from the preceding storm «Austen» on Friday also do not belong retrospectively in the Sunday balance.
There is also the difference between a short gust and wind averaged over a longer period. The well-known Beaufort scale refers to mean wind speeds. A single peak value therefore allows no blanket statement about how long a storm prevailed at a location or how great the risk of damage there was.
Different signals apply on lakes. The Bern cantonal police distinguish orange warning lights with roughly 40 and 90 flashes per minute for strong wind and storm. For people on the water, these local indications are more relevant than a distant summit record.
For the next planning, the current warning status counts, not just the retrospective view of «Boelo». The measurements explain why Sunday turned out very differently from region to region. But they justify neither a dramatic nationwide damage story nor the claim that precautionary restrictions were unnecessary because hardly any wind was noticeable elsewhere.
Sources
- MeteoSwiss: review of «Boelo», 26 October 2026
- Basel Autumn Fair: closures and reopening on 25 October
- Bern cantonal police: meaning of the storm warning signals
- Information platform of the building-protection sponsors: storm and wind measurement variables
- SRF Meteo: forecasts for «Austen» and «Boelo»
- MeteoSwiss: terms of use, source citation and image rights
