The months either side of summer are the best and the worst of the hiking year. Trails are empty, the light is long, the huts are closed and the ground has not decided whether it is winter or summer. Three hazards define the shoulder season and they are all, at root, about snow: the old snow that lingers on shaded slopes long after the valley is green, the avalanche terrain that a walker can wander into without any avalanche training, and the rivers fed by the melt of both. Here is how we read the three, and the rules of thumb we use to plan around them.
Why the north side is a different season
In the northern hemisphere a north-facing slope receives far less direct sun than a south-facing one, and in late spring the difference is measured in weeks. A trail that is dry and dusty on the south side of a pass at 2,200 m (7,200 ft) in May can drop onto a north side still holding a metre of snow, and that snow often lasts into July in the Alps, the Pyrenees and the Rockies at similar altitudes, and into August on high shaded ground. In autumn the process reverses: the first storms in September or October put snow on north aspects that does not melt again until the following June, while the south side stays walkable for weeks.
Old snow is not the soft powder of winter. Repeated melt and refreeze cycles turn it into neve: hard, dense, and at dawn as slick as a rink. In the morning, a north-facing gully at 35 degrees with a rock outcrop at the bottom is a place where a slip in trail shoes does not stop. By early afternoon the same slope has softened to knee-deep slush that is exhausting and collapses into hidden voids beside rocks and along stream lines. The window between too hard and too soft is often only a couple of hours, and it depends on aspect, altitude and how cold the night was. Our rules: for any route above the treeline between roughly April and mid-June, or after the first autumn snowfall, we assume snow on north and east aspects until a recent report says otherwise; we carry light traction devices and, on steeper ground, an ice axe we know how to use; and we time north-facing descents for late morning, when the surface has softened enough to kick steps but not yet turned to porridge.
Avalanche terrain for people who are not skiers
Walkers tend to assume that avalanches belong to winter and to skiers. In fact spring and autumn kill hikers with them every year, for a simple reason: the terrain that produces avalanches is defined by slope angle and snow, not by season, and a summer trail often crosses it. Most slab avalanches release on slopes between 30 and 45 degrees, with a peak around 38 degrees. Gentler than 30 degrees, the snow generally will not slide; steeper than about 50, it sluffs off continuously and rarely builds. A trail that zigzags up a 35-degree bowl to a col is, when there is snow on it, an avalanche slope, and being on foot with poles changes nothing.
The spring hazard is mostly wet snow. As the sun warms the pack, meltwater percolates down, weakens the bonds between grains and lubricates the base; wet loose avalanches and wet slabs run in the afternoon, often from south and west aspects first, and gliding avalanches – whole slabs creeping off smooth grass or rock – release unpredictably during warm spells. Autumn brings the opposite problem: early snow on warm ground or on old summer snow patches makes a poor base for the next storm, and a walker crossing a fresh 40 cm layer on a 35-degree slope is testing a slab.
Rules that need no rescue gear
Know the angle of the slope we are crossing: a phone inclinometer or the contour spacing on the map tells us, and 30 degrees is about where a staircase starts to feel steep. Avoid crossing or standing below any snow-covered slope steeper than 30 degrees on a warm afternoon. Cross one at a time, quickly, when there is no alternative. And read the regional avalanche bulletin where one is still issued, because its five-level danger scale applies as much to a walker on a boot-packed trail as to anyone on skis. When the bulletin says “considerable” (level 3 of 5) or higher, above-treeline routes are not walking routes.
The spring river problem
All that snow has to go somewhere. In the melt season a mountain stream runs on a daily cycle: lowest around dawn after a cold night, rising through the morning as the sun works on the snowfields above, peaking in the late afternoon or evening at two or three times the morning flow. A thigh-deep crossing at 07:00 can be impassable at 16:00, and rain on snow accelerates everything. Rivers below glaciers follow the same pattern with more sediment, which hides the bottom.
The physics is unforgiving. The force of moving water on the legs rises with the square of the current speed, and knee-deep water at 1.5 m/s is enough to unbalance an adult; thigh-deep at that speed, most people go in. Cold adds a second hazard: meltwater at 2 to 4 C causes gasping and loss of grip within a minute or two of immersion. This is why in many ranges more walkers drown in June than in any other month.
Our crossing discipline is fixed. Cross early in the day and plan the route so the biggest crossing comes first, not last. Look for wide, braided, shallow sections rather than narrow fast ones, and for a run-out downstream that is not a boulder field or a gorge. Unbuckle the hip belt and sternum strap so the pack can be shed. Face upstream, use poles as a third point, move one foot at a time, and turn back the moment the water reaches the thigh and the footing goes. A group can link arms in a line facing the current, strongest person upstream. And if the crossing is not on, it is not on: we camp, wait for dawn, or go around, which may cost a day.
Reading the season before leaving home
The most useful shoulder-season information is a recent report from someone who has been there: hut wardens, park rangers, trail associations, dated forum posts. Beyond that, the forecast freezing level over the previous week tells us how much melt has happened, satellite snow-cover maps show which aspects still hold snow, and the avalanche bulletin, where it runs into May or June, gives both the danger level and the aspects and altitudes of concern.
- Assume snow on north and east aspects above the treeline until proven otherwise; carry traction and, on steep ground, an axe.
- Treat any snow-covered slope over 30 degrees as avalanche terrain; avoid it after midday in spring.
- Time north-facing descents for late morning, river crossings for early morning.
- Read the avalanche bulletin as long as it is issued; level 3 means stay below the treeline.
- Build a spare day into any multi-day route that crosses snowmelt rivers.
The shoulder season rewards exactly the planning that the crowded summer lets us skip. Get the timing right and it gives us the mountains to ourselves; get it wrong and it gives us a north slope at dawn, a bowl at three in the afternoon, or a river at five – the three places nobody should meet it.