Everything about climate, temperature and weather in the mountains

The French are passionate about the weather, and even more so at holiday time! Never before has the weather had such an influence on our choice of holiday destination. We are increasingly weather-dependent. Against this backdrop, the mountains are having to battle against many of the prejudices that characterise the mountain climate in summer. Some of the most common are: cool or even cold temperatures, heavy rainfall, risk of snow, thunderstorms that rumble more than elsewhere…

There’s nothing wrong with these observations, but they need to be put into perspective. “The mountain climate is distinguished from other climates by its vertical dimension”, says meteorologist Serge Taboulot. “The slopes and their very different orientation to the sun have a strong influence on the mountain climate”. The risk of unstable phenomena, such as showers or thunderstorms, is therefore greater there than on the plains or the coast. “The mountains are the paroxysm of the micro-climate”, sums up the Grenoble-based meteorologist.

So, how cold are the mountains in summer?

It all depends on the slopes (north -ubac- or south -adret-) and the condition of the soil! In other words, the climatic rule that says you lose around 2°C every 300 metres has to be modified here.

“Take a south-facing slope at an altitude of 1,500 metres and a north-facing slope at 1,000 metres. The weather will be much better on the first, even though it’s 500 metres higher”. Similarly, the temperature will be higher in a mountain pasture than under a forest canopy, even if it is on a lower level. At 2,500 metres, on a south-facing slope sheltered from the sun’s rays, the mercury can easily rise above 25°C. Similarly, the temperature difference between day and night is greater in the mountains than on the plains because the air is drier.

What about frost and snow in summer?

“Early morning frosts are not uncommon in July and August, even at low altitudes. But as soon as the first rays appear, they disappear”. As for snow at this time of year, it’s a classic, but in the high mountains! “From 2000/2500 metres upwards, it’s very common for flakes to appear. In the Mont-Blanc massif, it even snows more often in summer than in winter at high altitude, because it’s not as cold”. But there are very few resorts above 2200 metres!

Is it fair to say that there are more thunderstorms here than elsewhere?

Undeniably, because of the topography, which acts as a barrier to the warm air masses. “In France, there are on average around twenty days of thunderstorms a year. In the mountains, it’s 40 days”. But, fortunately, a thunderstorm is a temporary episode. As soon as the cooler weather returns, it subsides and the fine weather returns!

Do climate changes make themselves felt in summer?

France’s mountain regions are those most affected by climate change. In the space of a century, temperatures at 1500 metres have risen by around 1.5°C, compared with 1°C elsewhere in the country. Today, the climate at 1350 metres is equivalent to that at 1000 metres in the 1960s. It is therefore milder in the mountains than it was 50 years ago. Scientists even speak of a relative Mediterraneanisation of the northern Alpine climate.

However, unlike the plains or the coast, there is no risk of heatwaves in the mountains, as the cold air flows downwards. And that’s good news for the summer appeal of the mountain ranges!