The statistical analysis shows no significant correlation between the burn time of the Böögg and the summer temperatures in the Swiss Plateau. Or, to put it another way: There is no evidence to support the supposed predictive nature of the Böögg.
Hot summer of 2003 "predicted"
It is noteworthy that, ahead of the hot summer of 2003, the Böögg had exploded after only 5 minutes and 42 seconds. However, this was obviously pure coincidence. Before the second-hottest summer in 2015 and the third-hottest summer in 2018, the burn time was between 20 and 21 minutes. In these two years, the Böögg was a poor forecaster. Even in 2019, with the fourth hottest summer on record, it did not provide an accurate forecast, burning for just under 18 minutes.
The Böögg is no weatherman
It is not surprising that the Böögg scores so poorly as a forecaster in this study. How is a burning snowman made of cotton wool supposed to have good predictive qualities? In reality, the burn time depends on the construction of the pyre, the humidity of the firewood and the weather on the day of the Sechseläuten. Last but not least, there is the all-important factor of how much fire accelerant is used. Nevertheless, although the Böögg's summer forecast cannot be scientifically supported, Zurich would certainly not be without its oracle.
Seasonal climate forecasts from MeteoSwiss
The seasonal forecast from MeteoSwiss provides somewhat more certainty about the coming summer. With the help of a numerical model, the climate can be forecast several months in advance.
With this forecast, when we compare the mean summer temperatures with the actual measured values, we do indeed see a statistically significant correlation. So the model is better than simple guesswork, even though there are false predictions every now and then. The climate outlook for the summer is available at the end of May each year.