The data indicate that this year's meteorological summer, i.e. the period from June to August 2019, will be the third-warmest since measurements began in 1864. A nationwide average temperature of more than 15 °C is expected. So far this has only been achieved in the summers 2003, 2015, 2017 and 2018. The main reason why this summer was again very warm was the intense heat in June and July.
Despite the heat, there was widespread rainfall this summer. August, in particular, produced significantly more precipitation than normal in some places, e.g. in northern Ticino or the Grisons.
MeteoSwiss has taken a closer look at the summer. You can find the blog article here (in German, French or Italian only):