Wind chill on a hike: how wind, cold and wet clothing affect you

Air temperature alone does not show how quickly you can cool down on a windy ridge. Wind, wet clothing, exposure and time all matter. Use the forecast and the group’s condition to decide when to add layers, leave the ridge or turn back.

How wind chill is estimated

Wind increases heat loss from exposed skin. A wind-chill index combines air temperature and wind speed to estimate that effect under defined conditions.

A fixed deduction per metre per second does not represent how wind chill is calculated. Read the method and limits for the forecast or calculator you use.

The index is an estimate of cooling on exposed skin. The value changes with temperature and wind, and does not measure your body temperature. Clothing, moisture and how long you are outside affect what happens to you.

For example, Environment and Climate Change Canada’s table gives the following values at an air temperature of −5°C.

• At 10 km/h of wind, about −9°C wind chill.
• At 20 km/h of wind, about −12°C wind chill.
• At 40 km/h of wind, about −14°C wind chill.

Canada includes wind chill in forecasts at 0°C or below with winds of at least 5 km/h. The US National Weather Service calculator has a different application range. Follow the limits of the source you use.

A wind-chill value does not account for the added cooling from wet clothing. Use air temperature, wind, precipitation and exposure together when planning layers and a safe descent.

Why wind matters on a mountain

A hike can take you from a sheltered valley to a windy pass or ridge. Look up conditions for each part of the route, including places where the group may have to wait.

Temperature often decreases with elevation, but the rate varies and a valley can sometimes be colder than higher slopes. Check a forecast for the elevations you will reach.

Ridges and gaps can have stronger wind and gusts than sheltered slopes. Local terrain and wind direction affect the difference. Check forecasts for the specific ridge and its descent.

Sweat and rain can wet your clothing. If you stop or enter the wind while wet, you may cool quickly. Change or add layers in a secure, sheltered place before getting cold.

How to read wind and gusts

Check both the sustained wind and gusts for the relevant hour and elevation. A strong gust can disrupt balance while a sustained wind can keep cooling you over time.

Signs on the ground matter too. If the wind prevents controlled movement or you cannot keep warm, stop in a secure place and reassess how to descend or shorten the route.

Clothing and decisions that reduce exposure

Prepare for wind and cold before leaving the trailhead. Look at what you can put on quickly and where you can stop out of the wind.

Layers and dry clothing

Keep a windproof outer layer accessible. If rain or wet snow is expected, carry a waterproof layer suited to the conditions. Put it on from a stable place before crossing exposed ground.

Cover exposed skin as conditions require and carry dry insulation. Check that gloves, hat and neck protection are practical to use without losing time or dexterity.

• Carry a windproof layer and suitable rain protection.
• Keep insulating layers dry in the pack.
• Use base layers suited to activity and change damp clothing in shelter if you can.
• Carry suitable gloves and head protection from the cold.

Reducing exposure on the route

Plan where you can pause, add clothing or take a shorter route. A turnaround should leave enough time and energy to finish the descent.

Choose a stable, sheltered place away from rockfall or terrain hazards for stops. Check the group for persistent shivering, unusual clumsiness or changes in speech or behaviour.

If forecast wind or cold exceeds what the group can manage, choose a less exposed route or postpone. Reassess if the conditions are worse than expected or a member of the group cannot stay warm.

Before setting out

Check temperature, precipitation, wind and gusts at the heights and times you will reach. Use wind chill within its stated range and pack for the conditions along the entire route.

Agree on a turnaround point and where the group can get sheltered. Put on dry or protective layers early and change the route if anyone is getting too cold to move or think clearly.

Suspected hypothermia is an emergency. Move to shelter if safe, insulate the person and replace wet clothing with dry layers if possible. Request help promptly. In Japan, call 119 for a medical emergency or 110 for mountain rescue and report your location.