Open Data Insight of the Day

There is a saying in Basel: “God must be a Basel citizen.” It reflects the playful belief that the weather during Fasnacht is usually pleasant, as if higher powers were looking after the celebration. But is that really true? We analysed 100 years of weather data to find out.

During the past 100 years, Fasnacht was not observed 12 times: from 1914-1918 and 1940-45 during the world wars, and in 2020 and 2021 during the COVID-19 pandemic. The weather for the reference year 2026 was warm. The average temperature was 11.4°C, with a minimum of 3.1°C and a maximum of 7.9°C. Total precipitation was 0.5 mm, falling on one day, and there was one clear day. This pleasant weather supports the hypothesis of divine intervention, but the rest of the article will analyse whether this is true for a longer time period.

Analysing temperature over the past 100 years reveals a long-term average of 2.8°C. The coldest Fasnacht was in 1956 with an average of -9.8°C, while the warmest was in 2003 at 11.6°C. The data shows a clear warming trend, with the reference year 2026 being significantly warmer than the long-term average. Recent decades have been markedly milder than earlier ones. This trend is visualised in Figure 1: temperature at Carnival in the last 100 years, while Figure 2 shows precipitation at Carnival during the last 100 years. Table 1 lists the years with the most extreme weather phenomena.

Regarding precipitation and cloudiness, the average total rainfall during Fasnacht is 4.6 mm. Dry years, with zero precipitation, occurred 38% of the time. The wettest year was 1970 with 24.3 mm of rain. No strong long-term trend in precipitation is evident. The data does not provide a direct measure of average cloud cover, but the frequency of clear days suggests variability. The findings indicate that while dry conditions are common, significant rain is not rare, challenging the notion of consistently perfect weather.

Snowfall during Fasnacht has been infrequent. Measurable snow occurred in 15 years. The most significant snowfall years, like 1956 and 1963, featured three snow days. Snow events were more common in earlier decades, with a visible long-term decline in frequency in recent years. In conclusion, while pleasant conditions occur, the statistical record shows substantial variability, with cold snaps, rain, and even snow being part of Fasnacht's history. The saying about consistently good weather does not hold up to the data.