Weather in Chamonix in August

You are now ready for the UTMB race and the only uncertainty that remains is the weather in Chamonix in August. Although it is difficult to make accurate forecasts, it is possible to identify trends based on the history of the weather in the region in previous years and the averages that have been established.

The dates of the UTMB

In 2022, the UTMB took place from Monday 22nd August to Sunday 28th August. Globally, from one year to the next, the UTMB is always organised in the last week of August. It is therefore this week that should be analysed from a statistical point of view in terms of weather.

Average temperatures

As far as the daytime and maximum temperatures are concerned, Chamonix has an average maximum temperature of 26°C for the last week of August. This suggests that the days will be sunny, but not too hot. The average daytime temperature is around 21°C, which is a pleasant and mild weather for running. As far as the minimum temperatures are concerned, the average is 10°C at night with some years being close to 6°C. Of course, these values are given for the Chamonix valley and much lower temperatures are to be expected at higher altitudes. It is therefore advisable to subtract 6.5°C for every 1000 metres of altitude, but sometimes it can be more! 

The state of the sky

On average, this late August period in Chamonix tends to be sunny with some cloudy spells but not too much rain. On average during the last week of August, it only rains one day in Chamonix and not continuously. We can therefore consider as probable light showers without too much chance of a completely blocked sky. Nevertheless, all these data should be taken with a pinch of salt as, historically, all weather episodes can be considered to occur at this time. It is thus possible to have a very hot episode, as well as rainy or even cool, without the likelihood of severe cold.