As in April, a lot is possible in terms of weather in May: it ranges from snow and frost to midsummer heat. In addition, the first heavy thunderstorms often occur as a result of the higher position of the sun and the decreasing snow cover of the mountains.
May with a wide range of weather!
May has a wide range of weather conditions, with cold air blasts from the north occurring from time to time. In extreme cases, the merry month can even surprise us again with wintry weather and snow down to low altitudes. Morning frost is also possible in isolated cases, especially in the first half of the month. In addition, as a result of the increasing solar energy and the progressive thawing of the snow in the mountains as warm, humid air masses flow in from the south to southwest, strong thunderstorms may already develop, preferably in the second half of the month.
Below, the date of the last snowfall, the lowest and highest May temperatures ever measured, the date of the first hot day and the time of the last frost for a few selected stations are used to show the entire possible weather range for the month of May.
Fig. 1: Snow on the mountains, lush green in the lowlands; Source: Roger Perret
Last fresh snowfall
During cold spells in May, it rarely happened that there was still measurable snowfall at low altitudes (at least 1 centimeter of fresh snow). This was the case in Bern, Chur, St. Gallen and Zurich-Kloten, for example. In some places, the last fresh snowfall even dates back to the second half of the month, with the last snowfall in St. Gallen being on May 29, 1961 (1 centimetre) and in Chur on May 24, 1983 (9 centimetres).
Lowest and highest May temperatures
Station | Lowest temperature | Date | Highest temperature | Date | Range | Data since |
Aarau | -1.9°C | 01.05.1976 | 32.7°C | 25.05.2009 | 34.6 | 1959 |
Bern | -3.6°C | 04.05.1941 | 31.4°C | 25.05.2009 | 35.0 | 1864 |
Basel | -2.6°C | 04.05.1941 | 32.8°C | 12.05.1912 | 35.4 | 1897 |
Chur | -1.1°C | 04.05.1979 | 34.0°C | 25.05.2009 | 35.1 | 1959 |
Geneva | -3.5°C | 01.05.1945 | 33.8°C | 24.05.2009 | 37.3 | 1864 |
Lugano | 1.5°C | 02.05.1942 | 31.0°C | 29.05.2001 | 32.5 | 1865 |
Lucerne | -2.2°C | 04.05.1941 | 32.0°C | 25.05.2009 | 34.2 | 1886 |
Sion | -1.7°C | 04.05.1967 | 35.1°C | 25.05.2009 | 36.8 | 1959 |
St. Gallen | -5.0°C | 08.05.1957 | 29.2°C | 05.05.2003 | 34.2 | 1892 |
Vaduz | -1.5°C | 01.05.1976 | 33.2°C | 20.05.2022 | 34.7 | 1971 |
Zurich Airport | -5.9°C | 01.05.1962 | 31.9°C | 25.05.2009 | 37.8 | 1959 |
The above table with the lowest and highest temperatures ever measured in May at some selected stations shows that, with the exception of the Lugano station, at least some isolated May frosts were recorded at all the stations under consideration; on May 1, 1962, almost -6 degrees were measured at Zurich Airport.
Date of the first hot day
Station | Date of the first hot day | Data since |
Aarau | 20.05.2022 (31.0°C) | 1959 |
Bern | 12.05.1867 (31.4°C) | 1864 |
Basel | 10.05.1945 (31.1°C) | 1897 |
Chur | 02.05.2005 (30.4°C) | 1959 |
Geneva | 11.05.2012 (30.0°C) | 1864 |
Lugano | 08.04.2011 (30.8°C) | 1865 |
Lucerne | 13.05.1945 (30.5°C) | 1886 |
Sion | 10.05.1958 (30.1°C) | 1959 |
St. Gallen | 12.06.2003 (30.2°C) | 1892 |
Vaduz | 02.05.2005 (30.7°C) | 1971 |
Zurich Airport | 13.05.1969 (30.3°C) | 1959 |
In addition, with the exception of the slightly higher station in St. Gallen, the first heat day occurred in May. In Lugano, the first heat day could even be measured as early as April. In Sion, temperatures of just over 35 degrees were recorded on May 25, 2009!
Date of the last frost
Station | Date of the last frost | Data since |
Aarau | 13.05.1972 (-0.2°C) | 1959 |
Bern | 02.06.1962 (-0.1°C) | 1864 |
Basel | 24.05.1905 (-0.2°C) | 1897 |
Chur | 07.05.1966 (-0.3°C) | 1959 |
Geneva | 25.05.1967 (-2.1°C) | 1864 |
Lugano | 22.04.1938 (-0.7°C) | 1865 |
Lucerne | 22.05.1887 (-0.2°C) | 1886 |
Sion | 05.05.1979 (-0.8°C) | 1959 |
St. Gallen | 23.05.1955 (-0.5°C) | 1892 |
Vaduz | 05.05.1979 (-0.5°C) | 1971 |
Zurich Airport | 21.05.1963 (-0.4°C) | 1959 |
If we look at the date of the last frost, we can see that, with the exception of Bern (June 2) and Lugano (April 22), it fell in May. May is also the time of the ice saints (May 11 to 15), when cold spells are said to occur more frequently. However, there is hardly any statistical evidence of this. But more on this in a separate blog soon.
Very different May in recent years
If you only look at the last few years, you can see the great variability of the month of May: while May 2022 was the warmest or second-warmest May since measurements began in many places and there were also some heat days, May 2021, together with May 2019, went down in the weather annals as the coolest of the last 30 years. May 2023, on the other hand, was quite unremarkable in terms of both the average temperature and the amount of precipitation across the country.
And May 2024?
Of course, this cannot be estimated at the moment. All that is clear is that there is still no stable high in sight and therefore no prolonged sunny and dry phase. The next few days will be characterized by a high-altitude low, with a changeable and occasionally wet weather character. In the medium term, temperatures are likely to be roughly in line with the season – subject to minor upward and downward outliers. However, the second half of the month, for which no trend can yet be given, will be decisive for the monthly balance.
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The content of this article has been at least partially computer translated from another language. Therefore, grammatical errors or inaccuracies are possible. Please note that the original language version of the article should be considered authoritative.