On May 3 last year, a man named Iestyn Pugh was found sitting on a wet rock above Llyn Idwal at 4:10 in the afternoon. He had walked up the Devil's Kitchen path in a light fleece and a thin shell, planning a four-hour loop. The air temperature was eight degrees Celsius. A steady rain had begun at one. By the time the team from Ogwen Valley Mountain Rescue reached him, his core temperature was thirty-three point eight.
He was not in a blizzard. He was not above the snowline. He was on a popular path in May, three kilometres from a busy car park, in the kind of weather most walkers consider mild.
Cold injury in the shoulder season is the single most common preventable emergency in temperate-country mountains. It is not produced by cold weather. It is produced by wet weather at the wrong temperature, with the wrong clothing, and a walker who has not yet recognised what is happening to their own body.
The threshold temperatures are worth memorising. They are not absolute, but they are useful.
At an air temperature of around 10 degrees Celsius, a wet walker in cotton can become hypothermic in two to three hours of inactivity. The same walker, in motion and dry, will not.
At 5 degrees Celsius, a walker with wet hands and no gloves loses fine motor control in the fingers in roughly twenty minutes. They can no longer reliably open a buckle, light a stove, or operate a zip. Most accidents in this range involve a walker who could no longer help themselves with equipment they were carrying.
At 0 degrees Celsius with wind, the wind-chill equivalent on exposed skin can fall to minus ten or below. Frostnip on cheeks and earlobes begins within thirty minutes of exposure for an unprotected walker. This is the temperature range that does the damage in spring on British and Irish hills and on shoulder-season days in the Whites, the Adirondacks, and the Cairngorms.
Below freezing in still air with dry clothing is, paradoxically, less dangerous than five degrees with rain. A January walker who has dressed for January is usually fine. A May walker who has dressed for May is the one mountain rescue meets at four in the afternoon.
Hypothermia does not announce itself. The first symptom is not shivering. It is poor judgement. A mildly hypothermic walker takes longer to make small decisions, makes more of them wrongly, and is reluctant to stop and address the cause. They will often deny they are cold. They will continue walking when stopping to put on a layer would be the correct choice.
The shivering follows. So does what mountain medicine textbooks call the umbles: stumbles, mumbles, fumbles, grumbles. By the time a walker is umbling, their core has dropped a degree. They need shelter, dry insulation, and warm fluids, in that order. They do not need to continue to the car. The car is the wrong destination. The right destination is somewhere dry, immediately.
Severe hypothermia, with a core below thirty-two degrees, is a medical emergency that requires evacuation and rewarming under supervision. A walker in this state should not be made to walk. They should be insulated from the ground, wrapped in dry layers and a vapor barrier, and watched until help arrives.
The practical implications for a shoulder-season day are straightforward.
First, the rule that determines whether a walker can self-rescue is not the air temperature but the air temperature plus precipitation plus wind. A nine-degree day with rain and a ten-knot wind has the same physiological effect as a still day at minus two.
Second, the walker's clothing has to handle the wettest, windiest hour of the day, not the average. In the shoulder season this means a fully waterproof shell over a synthetic or wool insulating layer, even on a forecast that calls for sun. Cotton, fleece without a shell, and thin down jackets in the rain are reliably the wrong answer.
Third, hands lose function before any other body system. A pair of waterproof shell mittens packed in a hip-belt pocket is the single most useful piece of cold-weather gear in May, June, September, and October in most temperate ranges.
Fourth, the walker who is most at risk on a cold spring day is not the unprepared beginner. It is the experienced walker who has done the route before in better weather and assumes the route is the same. The route is rarely the problem. The body is.
Fifth, food and warm drink genuinely help. A thermos of sweet tea and a flapjack at the half-hour mark of a cold descent does measurable good. It is one of the few pieces of folk advice in the mountain canon that the clinical literature supports without qualification.
Pugh, in the end, walked out with the rescue team after ninety minutes of rewarming in a casualty shelter on the ridge. He recovered fully. He told a reporter from the North Wales Daily Post that he had been on the hill maybe sixty times and had never considered the weather a problem before.
He was not wrong about the hill. He was wrong about the calendar. The hill in May is not the same hill as in June. The clothing that worked in June will not work in May.
A walker who has been cold once, properly cold, in the field rarely makes the same mistake again. The lesson, for those who would prefer not to learn it the hard way, is a small one: dress for the worst hour the forecast permits, carry a way to make hot drink, and turn around when the rain becomes steady at the wrong temperature. The hill will still be there in a month.
Astrid Pereira teaches navigation and emergency response at a national outdoor centre. She has treated more cases of shoulder-season hypothermia than winter hypothermia, by an order of magnitude.
