Planning a mountain day: passes, weather windows and the descent home

A big mountain day is a planning problem before it is a fitness problem. The riders who come home from a 3,000 metre day tired and happy, and the riders who come home shivering in the back of a car, are frequently the same fitness. What separated them was decided at a kitchen table the night before.

Most of what makes an alpine day go wrong is predictable. The pass is closed. The storm builds at two in the afternoon on a morning that started clear. The descent takes forty minutes at ten degrees in a soaked jersey. None of these are bad luck. They are the normal behaviour of mountains, and you can plan around all of them.

Check the road authority, not the map

A pass drawn on a map is a road that exists. It is not a road that is open. High cols across the Alps, Pyrenees and Dolomites close for the winter and reopen somewhere between late May and early July depending on the year's snowpack, and a late spring moves those dates by weeks.

The map will not tell you. Neither, reliably, will a routing app. What tells you is the road authority or the regional roads office — most publish a live pass status list, and in Switzerland, Austria, Italy and France these are updated through the spring. Check it, and check it again two days before, because a fresh snowfall in June closes a 2,700 m col for 48 hours without warning.

Two related traps. A pass can be open to cars and still have unswept gravel and meltwater on the descent, which is a different ride from a dry one. And a road can be open at the bottom and closed at a barrier three-quarters of the way up, which you discover after two hours of climbing. Where a route depends entirely on one col, have the answer before you leave rather than a hope.

The weather window is the real constraint

Mountains make their own weather, and the mechanism is not subtle. Air forced to rise over terrain cools, condenses, and forms cloud — the process behind orographic precipitation, which is why windward slopes are wetter than the plains beside them. Over a summer day, a second mechanism stacks on top: the slopes heat in the sun, warm air rises off them, and by the afternoon that convection has built into showers and thunderstorms.

The timing of this is one of the most consistent things in mountain meteorology. Studies of deep moist convection on the southern side of the Alps find a pronounced diurnal cycle with activity building through the day, and radar climatologies of Alpine hailstorms put the peak in the afternoon and early evening. A morning that is clear and still tells you almost nothing about four o'clock. It may in fact be the ingredient — a clear morning is what heats the slopes.

Hence the old alpine rule: be off the high ground by early afternoon. It is not superstition, it is a climatological tendency with a physical cause. Plan the day so the col is behind you by one or two o'clock, not so the col is reached at four. That single decision reshapes the whole schedule, because it means an early start is not optional on a big day.

The lapse rate, and why the descent is the dangerous part

Air cools with height. The standard free-air figure is about 6.5 °C per 1,000 m, and it is a useful first approximation: a valley at 24 °C implies roughly 13 °C at a col 1,700 m above it.

Be careful with how much weight you put on that number, though. Measurements of surface temperature lapse rates over real terrain show they vary a great deal — with season, with cloud, with time of day, and with whether cold air has pooled in the valley overnight. The 6.5 figure is an average of a quantity that is not very constant. Use it to know that the col is much colder, not to predict the col to a degree.

Then add the descent. You will spend 30 to 45 minutes going downhill at 40 to 60 km/h, generating almost no heat, in kit soaked from two hours of climbing. Wind chill indices are built from a model of exposed facial cooling rather than a wet torso at speed, so they understate what you are experiencing — but they make the direction clear enough, and the physiology is unambiguous: wet clothing in moving air removes heat very efficiently. The cold-injury guidance from sports medicine and the wilderness hypothermia guidelines both put damp clothing and wind at the centre of how people get into trouble in conditions well above freezing.

This is why the jacket in the back pocket is not a nicety. Cold hands cost you braking; cold judgement costs you the line. If you want the technique side of getting down safely, how to descend faster and safer covers it, and dressing for 0 to 15 °C covers what actually works at col temperatures.

What to carry

Size the day by vertical metres, not distance

In the mountains, distance is nearly meaningless. A 90 km day with 3,200 m of climbing is far harder than a 160 km rolling day. Plan from the vertical.

There is a usable approximation. Climbing rate in metres per hour is roughly 367 multiplied by the watts per kilogram you put into the climb. On a real road, something like 15 to 20% of your power goes to rolling resistance and air rather than upwards, so a practical figure is about 300 metres per hour for each sustained watt per kilogram. That is an estimate, and it drifts with gradient, bike weight and how much you are carrying — but it is close enough to size a day.

Use the W/kg you can genuinely hold for an hour when already tired, not your best twenty-minute number. The gap between those two is where alpine days go wrong. If you are unsure what yours is, pacing a climb with power is the place to start, and seated versus standing climbing covers holding it for an hour without wrecking yourself.

One honest note on altitude itself. Laboratory work in trained endurance athletes shows maximal oxygen uptake declining approximately linearly with altitude, on the order of 6 to 7% per 1,000 m, measurable from a few hundred metres upward. Whether you will notice that on a 2,000 m col is a different question — at those heights the effect is modest, partly offset by thinner air being easier to move through, and swamped by fatigue, heat and fuelling. Treat it as a reason your numbers may read a little low at altitude, not as an excuse or a training theory.

Water, and the long dry stretches

Alpine valleys have villages; alpine climbs mostly do not. A 20 km ascent can pass nothing at all between the last village and the col, and the refuge at the top may be shut on a Tuesday in June. Two bottles is often not enough on a hot day with 1,500 m of climbing in front of you.

Mark the water before you leave: village fountains, cemetery taps, refuges with their opening seasons, and the one bar in the hamlet at the foot of the climb. Assume a fraction of them will not be there. Our hydration guide covers how much you actually need; the planning job is making sure it is available where you need it.

Daylight in a valley is shorter than daylight

Sunset times are computed for a flat horizon. In a valley with 2,000 m walls, the sun goes behind the ridge long before that — often 90 minutes to two hours earlier on a north–south valley, and the shade arrives suddenly and cold. If your route ends with a long valley run-in, budget for it being dark and chilly before the forecast says it should be.

The same applies at the start. A 6 a.m. departure in a deep valley is a cold one, whatever the day turns into by eleven. This is another argument for the pocket jacket rather than the optimistic jersey.

Build the bail-outs before you need them

An alpine loop usually has a small number of points where you can cut it: a valley road that links back before the second col, a train in the bottom of the valley, a lift that runs in summer. Find them in advance and know their distances, because you will be making that decision at the worst possible moment — tired, at a junction, with weather coming in.

The useful habit is to write down two numbers for each decision point: how much further the full route is from there, and how much further the short version is. Keeping both versions saved is easier than improvising. Moveee's route library lets you hold the full loop and its cut-short variant together so the choice at the junction is a file, not a calculation. Whatever tool you use, the short version wants to exist before the day starts.

The mountains reward planning more than almost any other terrain, because the consequences of getting it wrong scale with the altitude you have to lose to fix it. Check the pass. Start early. Carry the jacket. Size the day from the vertical. Then the rest of it is just riding up a very beautiful road, which is what you came for.