* The measurement series from La Brévine (minimum and maximum temperatures) was homogenised in 2011. In the process of doing so, it was found that the minimum temperature of -41.8 °C measured on 12 January 1987 would have been equivalent to -42.5 °C under today's measurement conditions. The difference is due to the transition, in October 1997, from the former manual system of measurements (in a measuring hut) to an automatic measuring system.

** At the time, the Grono measurement station was located on the slope a little way above the village, hence the slightly higher altitude than today's location. Current measurement conditions on the valley floor would have given a maximum daytime temperature reading of 40.5 °C in Grono on 11 August 2003.

(1) These values are based on homogeneous series of measurements. Homogeneous means that any artificial changes in the data series have been eliminated.

(1) These values are based on homogeneous series of measurements. Homogeneous means that any artificial changes in the data series have been eliminated.

Heavy precipitation

The average of the highest precipitation sums over a specified period of a year provides information about the geographical distribution of heavy precipitation. This is shown in the following graph of one-day precipitation sums, in mm, (from 1961 to 2014).

The heaviest precipitation normally falls in Ticino, where the southern orographic effect is primarily responsible for the large amounts of rainfall. The peak amounts of rainfall found in the inner Alpine valleys, in particular, in the Rhone valley, are more modest in comparison. In the Swiss plateau, it is thunderstorms that are the main cause of heavy precipitation events, and it is unsurprising, therefore, that the heaviest precipitation in that region occurs primarily during the summer months.