In the mountains: recognising weather changes and turning back in time

When air has to rise over a mountain, it expands and cools as it does so. Cold air can hold less water vapour, so clouds form and it may rain or snow. On sunny summer days the heating of the ground adds to this: warm air rises during the morning, cumulus clouds grow, and in the afternoon they can turn into thunderstorms. That is why mountain hikes with an early start are often safer in summer.

On average it gets a little colder with every metre of height – roughly half a degree to one degree Celsius per hundred metres, depending on the weather. Add the wind, which often blows much harder on ridges and summits than in the valley and draws even more heat from the body. Someone who sets off in a T-shirt in the valley can be freezing higher up in wind, fog and drizzle, even in high summer.

Fog is an underestimated problem in the mountains. It forms when clouds hang on the slope or moist air cools. Within minutes, waymarks, cairns and drop-offs can disappear from view. Then an easy path suddenly becomes a difficult navigation task.

The turnaround time is the most important decision of the day, and it is best made at home or over breakfast with a clear head. Out on the mountain you are tired, want to reach the goal and get carried along by the group. Mountaineers sometimes call this “summit fever”. A fixed time removes that pressure: there is no discussion, you turn round.

The mountain forecast gives information on thunderstorm risk, wind, visibility and the freezing level – the height above which it is below zero. If it is low, there may be snow or icy patches higher up. An uncertain forecast is not a reason to “just give it a try” but a reason for a shorter route with good escape options.

On the way your own observation counts. Warning signs are cumulus clouds that grow quickly upwards and darken at the base, freshening or shifting wind, a noticeable drop in temperature and fog creeping up from the valley. Put on your rain jacket and warm layer before you are wet and cold – afterwards it is much harder to warm up again.

In a thunderstorm, summits, ridges, isolated trees and fixed cables on via ferratas are especially dangerous because lightning tends to strike high, exposed points and metal. If you can hear thunder, the storm is close enough to be dangerous. Then descend quickly from exposed places and avoid gullies where water collects. A hut or solid building is the best protection.

Hypothermia is possible even in summer when wetness, wind and exhaustion come together. Warning signs are intense shivering, clumsiness, stumbling, slurred speech and confusion. Then seek shelter from the wind at once, put on dry and warm clothing and call the local emergency number (112 in the EU).

If you have no signal, there is the alpine distress signal: give a signal six times a minute, for example with a whistle, a light or shouts, then pause for one minute and repeat. The reply is three times a minute. In fog and when unsure of the way: stop, work out your position and do not carry on into the unknown.

Practise reading the weather on easy routes where nothing is at stake. Check the mountain forecast in the morning and compare it during the day with what you see: when do the first cumulus clouds form, how fast do they grow, when does the wind pick up? That way you develop a feel for the signs.

Make the turnaround time a habit, even on short routes. Say it out loud in the group and write it down. Once you have felt how good it is to be back in time, it is easier to stick to it next time.

This knowledge is not enough for alpine tours, via ferratas, glaciers or winter trips. For those there are courses with alpine clubs and mountain schools, or certified mountain guides who take you along and show you how decisions are made on the ground.