Navigating at night, in fog and in whiteout

In good visibility you usually navigate without noticing: you constantly compare what you see with what the map shows. In poor visibility this matching disappears. So you replace seeing with three measurable quantities: direction (with the compass), distance (with pace counting and time) and – in the mountains – height (with an altimeter or from the slope under your feet). Each of these has errors, but together they give a fairly reliable picture.

The trick is short legs. A small error in direction grows with every metre: on a long leg you can pass far wide of the target, on a short one the deviation stays small. That is why you choose a leg target that is unambiguous and large, something you cannot miss even in poor visibility – a path junction, a stream, the foot of a slope. Long lines in the terrain such as paths, fences or streams serve as 'handrails' you follow along, or as 'catching features' that tell you: this far and no further.

Your eyes themselves matter too. In the dark they slowly adjust to low light; this takes many minutes. A bright beam quickly undoes this adaptation. Dimmed or red light disturbs it less, which is why many headlamps have a red-light mode.

What matters most is the honest question at the start: carry on or wait? On a known, clearly visible path you can make safe progress even at night or in fog. In steep, unknown or trackless terrain, however, it is often wiser to stop, wrap up warmly and wait for better light or for help. Many accidents happen not because people stop but because they push on under time pressure.

If you do carry on, go slowly and check often. Note when you start each leg and count your paces. If the expected feature does not appear, that is a warning sign: stop and think, instead of walking 'just a bit further'. For direction, 'leapfrogging' helps: one person walks ahead a short way with a light and stops on the compass bearing, the others walk up to them – and so the group moves from point to point.

Plan your light like a supply. Cold makes batteries weaken faster. Spare batteries or a second small lamp belong within reach in a jacket pocket, not at the bottom of the pack. And do not rely only on your phone's GPS: when its battery is flat, you need map and compass.

In fog, people lose each other at short distances. Keep the group within sight and earshot, never let anyone run ahead or fall behind alone, and count heads regularly. Agree beforehand what someone who loses contact should do: stay put and shout or blow a whistle.

In a whiteout on snow all contrast is gone. You can no longer see whether the ground goes up or down, and edges, cornices or drops are barely visible. Here waiting or retreating along your own ascent track is often safer than any navigation. Glacier and avalanche terrain require their own training; this entry is no guide to it.

If you stop, think about the cold. Even in summer you cool down quickly at night in the mountains or in wet fog. Put on dry layers before you start to shiver, sit on insulation rather than the bare ground, and call for help early if someone is injured, exhausted or very cold.

Practise first by day on a known path: measure your pace count for a hundred metres, walk compass legs and see how accurately you arrive. Then repeat this at dusk and later in the dark on the same safe ground. This teaches you how your steps shorten in the dark and how much slower everything becomes.

A good exercise is a short evening loop you know well: lamp mostly dimmed, brighter only for reading the map. Notice how long your eyes take to get used to the dark again. Also make a habit of setting a turnaround time on trips – the best night navigation is the kind you never need because you are back before dark.