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Hot spell pushes ‘zero-degree’ line to record height in Switzerland

A hot spell enveloping Europe has pushed the zero-degree line -- the altitude at which the temperature dips into the minus -- to a record height of nearly 5,300 metres (17,400 feet) in Switzerland.

Published: 21 August 2023 09:13 CEST

The Grimsel Pass, Obergoms, in Switzerland.

The Grimsel Pass, Obergoms, in Switzerland. Photo by Samuel Ferrara on Unsplash

The zero-degree line is determined by meteorologists using weather balloons that take off twice a day from Payerne in western Switzerland.

MeteoSwiss said the new height was clocked overnight from Sunday to Monday at 5,298 metres, “which constitutes a record since monitoring began in 1954”.

The previous record of 5,184 metres was set on July 25th last year.

“The area known as the zero-degree isotherm is the threshold between air layers with temperatures above 0C at lower altitudes and those with temperatures below freezing at higher altitudes,” MeteoSwiss said.

“Among other things, the zero-degree isotherm affects vegetation, the snow line and the water cycle, and so has a considerable impact on the habitats of humans, animals and plants alike,” it added, calling the marker “an integral part of weather forecasts in the Alpine region”.

Switzerland has been experiencing a sweltering hot weather over the last week, with several heat warnings in place. The heatwave is set to continue for a few more days.

READ ALSO: How long will Switzerland’s heatwave last?

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Will Switzerland be visited by 'Ice Saints' this year?

From May 11th to the 15th, a meteorological event takes place each year in Switzerland.

It “observes”, though admittedly not on scientific basis, a centuries-old weather phenomenon called “Ice Saints”.

What exactly is it?

As its name suggests, it is related to saints, as well as ice and frost.

The saints in question are St Mamertus, St Pancras, St Servatius and St Boniface.

According to a weather lore, once these Ice Saints have passed through Switzerland in the middle of May, frost will no longer pose a threat to farmers and their land.

As the official government meteorological service MeteoSwiss explains it, “spring frosts have been a regular occurrence for centuries, giving rise to the traditional belief that a blast of cold air often arrives in the middle of May. Over time, this piece of weather lore became known as the Ice Saints.”

Fact versus myth

You may be wondering whether the Ice Saints lore actually has basis in reality.

Records, which date back to 1965 and originate from the Geneva-Cointrin, Payerne, and Zurich-Kloten weather stations, “clearly show that, over the long-term average, frost directly above the soil is only a regular occurrence up until the middle of April”, MeteoSwiss says. “After that, the frequency with which ground frost occurs progressively declines to almost zero by the end of May.”

“We can conclude, therefore, that there is no evidence in Switzerland to confirm the Ice Saints as a period in May when ground frost is more common.”

However, MeteoSwiss does concede that “ground frost is nevertheless a regular occurrence throughout May as a whole…having occurred at least once or twice in May every year, and in around 40 percent of the years there were more than two days in May with ground frost.”

What about this year?

MeteoSwiss weather forecast for the next seven days indicates that, this year too, no frost will be present on the ground in mid-May.

In fact, temperatures through much of Switzerland will be in double digits, reaching between 18C and 25C, depending on the region.

You can see what to expect in your area, here.

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