Not a heatwave Why the federal government is not warning of heat despite 33 degrees
Switzerland is currently experiencing the first major heatwave of the year. Temperatures of over 30 degrees have been measured in several places. Nevertheless, MeteoSwiss is not yet talking about an official heatwave.
27.05.2026, 09:01
27.05.2026, 10:02
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- Despite temperatures of over 30 degrees, the current weather situation is not yet officially considered a heatwave.
- The decisive factor for MeteoSwiss is not the maximum value in the afternoon, but the average temperature over 24 hours.
- Because the nights have remained relatively cool so far, the heart and circulation have been able to recover sufficiently.
Switzerland has experienced its first heatwave of the year with temperatures well over 30 degrees in some places. However, there can be no talk of an official heatwave.
The Federal Office of Meteorology and Climatology (MeteoSwiss) only speaks of a heatwave when a daily average temperature of 25 degrees or more is reached on at least three consecutive days. If the criteria are only met for a maximum period of two days, this is referred to as a short heatwave.
The decisive word is average temperature: the average of a full 24 hours counts here - including the cool night and morning hours. Even though temperatures rose to over 30 degrees at many measuring stations during the day, the official threshold was clearly missed.
For example, temperatures at the Basel-Binningen measuring station reached 32.5 degrees on Tuesday. The average daily temperature, however, was 24.2 degrees, below the 25-degree threshold. At the measuring station in Sion, temperatures even reached 33.9 degrees on Tuesday - but here, too, the daily average temperature of 24.7 degrees Celsius was well below the heatwave threshold. On the previous days, it was even cooler.
Cooling down at night helps the circulation
There is a medical reason why meteorologists look at the 24-hour average for heat warnings. For the human body and the cardiovascular system, the short-term heat peak in the afternoon is not the biggest problem. The decisive factor is the night: if it remains oppressively hot and humid, the body is constantly running at full speed. The blood vessels remain dilated, the pulse high and sleep is not very restful.
However, because it cooled down considerably at night on this Whitsun weekend, the heart and circulation got a much-needed rest.
There were already hot days earlier in the year
The term "heat day" is a different matter. For a day to go down in the statistics as a heatwave day, the mercury only has to break the 30 degree mark at its hottest moment. Basel and Sion therefore experienced heatwave days by definition on Whit Sunday, even if it wasn't enough for a heatwave.
The fact that it is so warm at Whitsun is "unusual, but not record-breaking", wrote MeteoSwiss in a blog post last week. The earliest hot day was even further back in the calendar. At the Basel-Binningen station (in 1945) and in Sion (in 1958), the earliest heatwave day was recorded on May 10. The earliest heatwave day in the whole of Switzerland was recorded in Lugano in 2011 on April 8.
On a long-term average, however, the first hot day in the Swiss lowlands is not reached until June - usually on June 7 in Sion and June 9 in Basel-Binningen.
