Staying Safe in Thunderstorms Above the Treeline

Why the Fells Make Their Own Weather

The British hills are modest in height but remarkably good at brewing trouble. A warm afternoon, a moist south-westerly and a ridge line rising into cooler air is all it takes. Air is forced upwards over the slope, cools, condenses, and before long a cumulonimbus is sitting directly over the summit you were planning to have lunch on. On Snowdon, the Cairngorms, the Lakes or the Brecon Beacons, the terrain itself can trigger the storm, which means the forecast you read at breakfast may not reflect what is happening above your head at two in the afternoon.

Lightning in the UK is not a rare curiosity. It kills or injures a handful of people each year, and hill walkers, climbers and campers are over-represented among the casualties. The good news is that the vast majority of those incidents are entirely avoidable with a bit of planning and a willingness to turn around.

Read the Sky and the Forecast Properly

Before you leave the car park, look at a mountain-specific forecast rather than a town one. You want the convective outlook, the timing of any thundery showers, and the wind direction at summit level. A phrase like "scattered heavy showers, thundery at times" in a hill forecast is a serious warning, not background noise.

• Cloud build-up: Towering cumulus that grows through the morning, with flat, dark bases and a hard, anvil-shaped top, is the classic thunderstorm in the making.
• Sound: Count the seconds between a flash and the thunder. Every five seconds is roughly a mile. If the gap is closing, the storm is coming to you.
• Hair and equipment: Hair standing on end, a crackling sound, or a faint tingling on metal is a warning that a strike is imminent. Do not run. Crouch immediately.
• Hail and sudden cold: A drop in temperature with hail often signals the downdraught of a mature storm cell.

Leave the Ridges and Summits Early

The single most effective thing you can do is not be on the high ground when the storm arrives. Ridges, summits, cols, exposed crags and the top of any slope are all places where you become part of the landscape's electrical circuit. Plan your day so that you are off the tops by early afternoon in summer, when thunderstorms peak.

If you see a storm developing and you are still climbing, turn around. It is frustrating, and it will feel excessive nine times out of ten, but that tenth time is the one that matters. Descending a broad, sheltered valley is far safer than pressing on to a summit cairn and hoping. Aim for lower ground, ideally a valley floor or a broad basin well away from water features.

Where Not to Shelter

When the storm is overhead, the rules are simple and worth memorising.

• Avoid isolated trees and small clumps of trees. They attract strikes. A dense wood of uniform height is better, but the best shelter is a low, broad stand of trees or a proper building.
• Avoid water — lochs, tarns, streams, boggy ground and wet gullies all conduct electricity extremely well.
• Avoid cave mouths, overhangs and shallow rock shelters. The current can arc across the opening. Go deeper or stay out.
• Avoid wire fences, gates, stiles, metal posts and via ferrata cables. These can carry current a long way from the strike point.
• Avoid exposed summits, ridge lines and the tops of screes. Crouch lower down the slope instead.

The Crouch, and Keeping the Group Apart

If you are caught in the open with no time to descend, get into the lightning position. Squat down on your sleeping mat, rucksack, rope coil or any dry insulating layer. Keep your feet together and your head tucked down, hands over your ears. Do not lie flat — that puts your whole body in the current path between ground points. Do not sit on wet rock. A crouch on a mat reduces the potential difference across your body if a strike lands nearby.

Groups should spread out. This is counter-intuitive when everyone is frightened, but a tight huddle is exactly what you don't want. Aim for at least ten to fifteen metres between people, so that a single strike cannot injure the whole party, and so that whoever is unhurt can help. Keep an eye on each other from a distance. If someone is struck, the priority is their breathing and circulation; call for help as soon as it is safe to move.

Wild Camping and the Small Hours

Thunderstorms often arrive after dark. If you are wild camping above the treeline, pitch low and away from water, ridges and isolated trees, and avoid the highest point of any flat area. Tents offer no protection from lightning, and poles and guy lines can conduct. If a storm builds in the night, leave the tent and take up the crouch on your mat, well spaced from your walking partner.

After the storm passes, wait at least thirty minutes from the last thunder before moving back onto high ground. Then check your route, your gear and your mates. The hills will still be there tomorrow, and so, with a bit of care, will you.