Weather on Aconcagua is dictated not by the calendar but by the combination of altitude, wind and the rapid movement of weather systems across the Andes. Within the same period, different expeditions can get a dry route, heavy snowfall, several days of strong wind or a short summit window.
The main season
Most commercial ascents take place in the southern hemisphere summer, usually from the middle of November to the end of February. The exact dates on which routes, services and rate periods operate are set for each season. Outside the main window, access and support may be limited.
Choosing January over December does not in itself make an expedition safe. The month affects the statistical likelihood of certain conditions; it gives you no forecast for a particular day.
The main weather factors
Wind
Strong wind increases heat loss, makes movement harder, destroys tents and can close off any chance of a safe summit push even under a clear sky. On Aconcagua the term viento blanco, or “white wind”, is used for the dangerous combination of strong wind and blowing snow, which drastically reduces visibility and the ability to navigate.
The decision to set off does not rest on a single number in a forecast. Wind direction and gusts, temperature, precipitation, the state of the slope, visibility, the length of the route and how much the team has left in reserve are all weighed up.
Cold and sun act at the same time
In dry air and open sunshine the day can feel warm, but shade, evening and wind change the felt temperature very quickly. At altitude the body produces less heat once it is tired, and dehydration and poor eating make the problem worse.
You need a layering system you can adjust without stopping completely: a base layer, insulation, a windproof and waterproof shell, a warm down jacket, spare gloves, face protection, sunglasses and goggles. The precise list is published on the page for each programme.
Snow and the state of the route
The Normal Route is often largely dry, but snow and ice can appear at any point in the season. After a fall of snow, grip, visibility and speed of movement all change. Whether crampons and an ice axe are used is decided according to current conditions, and you must be able to use the equipment issued to you or your own.
Why contingency days matter
Contingency is not free time that can be trimmed in advance in exchange for a cheaper ticket. It allows the team to:
- postpone the summit push in strong wind or precipitation
- give the group extra recovery time
- avoid a dangerous decision forced by a fixed return flight
- reorganise the stages if the state of the route changes
Even so, having contingency does not oblige the team to wait until the last day. If there is no safe window, the expedition ends without a summit.
How to read a forecast
A mountain forecast is useful as a scenario, not as a promise. You compare several updates, look at the trend by altitude and cross-check the model against observations on the ground. The higher the camp and the further out the forecast, the more cautious your reading should be.
It is important not to argue with the team’s decision on the strength of a screenshot from one app. The guide weighs the forecast against actual conditions and against the time the whole group will need.
How to choose your dates
First choose an officially open period with working logistics, then a programme with enough margin. For a first ascent at this altitude, time for acclimatisation and for waiting matters more than the shortest possible schedule.
Take a look at our comparison of the 17, 12 and 7 day programmes and the general guide to Aconcagua. All current formats are listed on the destination page.
Why a Mendoza forecast does not describe Aconcagua
The city, base camp and an altitude of around 7000 m are in entirely different conditions. A warm day in Mendoza tells you nothing about the wind at Nido de Cóndores or the temperature during a night start from Cólera. The forecast is assessed across several altitude points and updated continuously as you move.
| Factor | What it can change |
|---|---|
| Strong wind | The summit push, the pace, the stops or the decision to turn back |
| Fresh snow | The terrain, work in crampons and the time needed |
| Severe cold | Insulation, keeping hands warm and whether equipment works |
| Poor visibility | Navigation and assessment of route conditions |
| Precipitation lower down | The approach, the stages and the work of the ground logistics |
The season and official dates
The main season falls in the southern hemisphere summer, but the official access periods, permit categories and operating services are set anew each year. They have to be checked for the current season rather than inferred from the dates of a previous trip.
Before choosing, open the dates of the 17-day programme, the equipment list, our analysis of summit day and the official park information.
A weather checklist for climbers
- Know which set of clothing has been designated for the day’s push.
- Carry spare warm gloves and face protection.
- Protect your head torch, phone and batteries from the cold.
- Know the order of movement and the signal for turning back.
- Do not change your equipment after the briefing without agreement.
- Keep a dry set aside for recovery in camp.
Check your equipment against the full list, and your practical camp routine against our guide to daily life on the route.
A weather plan for each stage of the expedition
| Stage | What is checked | Possible decision |
|---|---|---|
| The approach | Precipitation, wind in the valley and the state of the trail | Departure time and order of movement |
| Plaza de Mulas | The forecast for the upper mountain and recovery | Move up, rest or change the cycle |
| High camps | Wind, cold, snow and the tents | Move, wait or descend |
| Summit day | Gusts, temperature, visibility and time | Start, postpone or cancel |
| The descent | Residual weather and the state of the route | Pace, group order and where to spend the night |
How contingency is used after bad weather
After a day of storm the team may need not only a new window but also recovery. Poor sleep, dehydration, damaged equipment and extra work in camp all change how ready you are. Contingency is not an automatic second attempt: sometimes the right way to use it is a safe descent.
What the daily briefing should cover
- the forecast by altitude and by time of day
- actual observations from the camps
- the plan of movement and the checkpoint decisions
- clothing, water and food for the stage
- how the group will communicate
- the conditions for changing or cancelling the plan
You should understand not just the start time but the reasoning behind the decision. An early wake-up, a packed rucksack or contingency already spent are not reasons to carry on in deteriorating conditions.
What to ask before you pay
- how many contingency days are built into the route
- who receives and interprets the forecast
- who takes the final decision on the start
- what happens when a move between camps is postponed
- what costs arise if the programme changes
- how communications with the high camps are organised
Your personal routine
Before setting off you know where your spare gloves are, how your water and batteries are protected, which layer goes on first and who to tell if there is a problem. You do not wait for a long halt if your fingers go numb, if you cannot get warm, if you lose your balance, if your goggles are damaged or if your head torch fails.
After each stage the kit is adjusted. If you could not get at your food, or your face mask fouled your goggles, fix the problem before the next push, not on the summit.
Why the forecast has to be read by altitude zone
Conditions on the approach, at Plaza de Mulas, at Nido de Cóndores and at Cólera cannot be reduced to a single forecast point. The higher the team, the more wind and cold affect how fast routine tasks can be done, the condition of the tents and whether it is possible to continue safely. A warm day in Mendoza is no argument for the upper mountain.
| Zone | What is checked | What it affects |
|---|---|---|
| Mendoza and the park entrance | Precipitation, roads and the ground logistics | Departure, baggage and the start of the route |
| Confluencia and the approach | Wind in the valley, precipitation and temperature | Stage timing, clothing and recovery |
| Plaza de Mulas | The trend on the upper mountain and actual observations | The first high-altitude cycle, or rest |
| Nido and Cólera | Gusts, severe cold, snow and the state of the tents | Moving camp, waiting or descending |
| The summit route | Hour-by-hour wind, visibility, cold and precipitation | The start, the checkpoint decisions and turning back |
The forecast by altitude is compared against the guides’ observations. If the model and the actual situation diverge, the decision is taken on the basis of the real route, not the most convenient screenshot.
How the decision changes from a long-range forecast to the start
Several days out, a forecast is for building scenarios, not for appointing a summit date. At base camp it helps you choose the sequence of the high-altitude cycle. In the high camp the horizon shortens, and immediately before the push the actual wind, cloud, temperature, snow and the condition of the group are all taken into account.
| Moment | Reasonable decision | What not to do |
|---|---|---|
| Before the trip | Prepare clothing, contingency and a flexible ticket | Fix a summit day |
| At base camp | Plan the cycle and possible waiting time | Ignore how the group is recovering |
| Before moving higher | Check the tents, the route and the window for returning | Go up simply because the day is paid for |
| Before the start | Begin, postpone or cancel the attempt | Treat a packed rucksack as a commitment to set off |
| While moving | Update the decision as facts change | Carry on because of the distance already covered |
Wind as a factor of time, not just temperature
Wind increases cooling and at the same time slows down changing clothes, eating, pitching camp and moving as a group. Even someone who does not subjectively feel cold may spend longer on every task. So what is assessed is the wind speed and the gusts, how long you will be exposed and how sheltered the section is.
Adjust clothing before you get noticeably cold. Keep spare gloves, face protection and goggles within easy reach. If you cannot warm your hands, hold the pace or handle your equipment safely, tell the guide straight away.
What happens to contingency after a storm day
Bad weather ending does not mean the team is ready. Sleep, food, water, the state of the tents, wet gear and general fatigue are all reviewed. Sometimes the next day is needed for recovery rather than for an immediate second attempt.
Contingency belongs to the leader’s route decisions. It can be spent on waiting, on recovery, on moving camp or on a safe descent. You should not build a non-refundable plan around a date that is contingency within the programme.
Tickets and your own weather margin
Contingency on the mountain does not replace a margin around the international trip. Before buying a ticket, check the change conditions, the baggage rules and the time available after the official end of the programme. The cheapest, most restrictive fare can create pressure to give up sensible waiting, or a sensible descent.
Your personal financial reserve is calculated from your own ticket and your own route to Mendoza. A universal figure in an article would be misleading. Nor does weather in itself guarantee an insurance payout: the grounds have to be checked against the specific policy.
Checking camp and kit after bad weather
Before the next push the team checks more than the new forecast. Tents, poles, guy lines, sleeping bags, clothing, stoves, torches and batteries may have been damaged or soaked. Damage that is tolerable at Plaza de Mulas can be critical at Cólera.
| Check | What to settle before going up |
|---|---|
| Tents | Serviceability, anchoring and how places are allocated |
| Clothing and sleeping bag | Whether the critical layers have dried |
| Stove and fuel | Whether you can produce water and cook |
| Electronics | Charge, spares and protection from the cold |
| The people | Sleep, appetite, warmth and readiness to move |
If the kit or a member of the team has not recovered, a window that opens may be missed. That is not a chance lost to caution but a consequence of how ready the team actually is.
The result of the check is announced at the briefing. Everyone knows what they personally have to put right, what the team will replace and when the next assessment takes place. A fault is not concealed in order to protect a stated departure time. Once repaired, the kit is checked again by the whole team before packing and moving up to the next high camp. The outcome is recorded in the plan for the next push.
Choosing your dates? Match the season and the available contingency against all the Aconcagua programmes, and then check the current forecast for the specific departure you have chosen.
Fact-checked: 17 August 2026. The forecast and the park regulations must be checked for your specific dates.