What spring temperatures reveal about the climate

Like other European countries, Switzerland experienced record-breaking temperatures in May 2026. Keystone / Gian Ehrenzeller

The spring of 2026 ended with unprecedented heat, capping a season that will go down as one of the most remarkable in Switzerland’s meteorological history. Forecasts now suggest that summer is also likely to be warmer than average.

The figures speak for themselves. May 2026 ranked as the seventh warmest May since national measurements began in 1864.

In the final week of the month, a persistent high-pressure system triggered a heatwave across much of continental Europe. Switzerland was no exception, with the southern Alps particularly affected. In Biasca, canton Ticino, temperatures climbed to 34.8°C on May 28 – just 0.3°C shy of the national May record.

An extraordinarily warm spring

While the late-May heatwave drew attention, it was the culmination of an exceptional season. With a national average temperature of 6.5°C across March, April, and May, spring 2026 was 1.6°C warmer than the 1991–2020 reference period.

This places it as the third-warmest spring on record, trailing only 2011 (6.83°C) and 2007 (6.65°C).

These figures reflect a broader and well-documented trend. Since records began in 1864, spring temperatures in Switzerland have risen steadily, with a marked acceleration from the 1990s onward. Today, spring is on average 2.9°C warmer than during the pre-industrial period (1871–1900).

The last cooler-than-average spring occurred in 2021. Even more striking, the ten coldest springs on record all date from before 1970.

A warming trend across all regions

The warming trend is evident throughout the country, regardless of region or altitude. The contrast is particularly pronounced south of the Alps, where long-term temperature records show a clear shift: earlier decades dominated by cooler years have given way to a succession of increasingly warm – often record-breaking – years since the 2000s.

What to expect from summer 2026

A warm spring does not necessarily guarantee a hot summer. Historical data suggests little direct correlation. Following the record spring of 2011, summer temperatures returned to near-average levels (13.18°C), and a similar pattern was observed in 2007 (12.98°C).

An exception came in 2022, when a moderately warm spring (6.17°C) was followed by an exceptionally hot summer (16.16°C), though such sequences remain relatively rare.

El Niño raises the stakes

This year, however, an additional factor may tilt the odds: El Niño. According to MeteoSwiss, sea surface temperatures in the equatorial Pacific region are rising rapidly, with potential global impacts expected as early as May–July 2026.

Although Switzerland lies far from the phenomenon’s origin, El Niño conditions tend to increase the likelihood of warmer-than-average conditions in many regions. MeteoSwiss’s seasonal outlookExternal link, issued in May, assigns a roughly 63% probability to a hot summer in western Switzerland – almost double the climatological baseline of 33%.

That said, MeteoSwiss stresses that seasonal forecasts for Switzerland remain uncertain, despite recent improvements. As is often the case with weather and climate, strong signals do not equate to certainty.

How Swiss temperatures are measured?

The Swiss mean temperatureExternal link reflects the average across the country’s surface, incorporating measurements from different altitudes and regions. It is based on the average monthly temperature (in degrees Celsius, measured two metres above the ground, based on measurements taken every ten minutes, day and night). These monthly values are then aggregated into seasonal and annual means. As such, it represents an average rather than extreme values, which can make some figures appear relatively modest.

This national indicator relies on long-term data from 19External link reference stations with uninterrupted records dating back to 1864. These include locations such as Basel/Binningen, Geneva/Cointrin, Davos, Lugano and Zurich/Fluntern. The measurement series have been homogenised to ensure consistency over time, and weighting factors are kept constant.

More broadly, MeteoSwiss operates around 160 automatic stations through its SwissMetNet network. For long-term climate monitoring, however, only the 19 NBCN reference stations are used.

Switzerland is divided into different climatic regions. In terms of long-term temperature trends, there are differences between the north and south of the Alps, and between different altitudes. For this reason, an average temperature has been calculated using the same method as for Switzerland as a whole. Climate trends are analysed across three sub-regions: north of the Alps below 1,000 metres, north of the Alps above 1,000 metres, and south of the Alps (including Ticino, the Simplon region, and southern valleys of Graubünden). The 19 reference stations are included for the sub-regions.

Adapted from French with AI/sb/ts