Windchill Factor: How cold it really feels

Every hiker is familiar with this phenomenon: You scale the summit, arrive sweating at the top, and as soon as you are exposed to the wind the intense shivering begins. This factor known as wind chill and should not be underestimated, as it can quickly lead to problems if you are exposed for prolonged periods. The consequences can include hypothermia and frostbite. In our article you will learn how the wind chill factor is calculated and what to do in the worst case scenario, to prevent and treat frostbite.

What is the wind chill factor?

Put simply, wind chill describes the difference between the actual and the apparent temperature in the cold. It is defined for temperatures under the 10°C mark. Here is what happens: Wind – whether it is actual wind or only drafts, like you might experience during long ski runs – removes the relatively warm air from the surface of the skin, thus allowing more cooling by evaporation.

So wind chill has less to do with the "temperature" and is rather more a measure of heat loss. The factor is only defined as temperature for the sake of simplicity.

But this quickly leads to misunderstandings. Here is a quick example: If the outside temperature is around 5°C and there is a wind speed of 50 km/h, the wind chill temperature will be around – 1°C. However, because of the higher absolute ambient temperature this will never lead to frostbite.

The wind chill factor is also a very subjective value, which is influenced by many different factors, such as body hair, warming lotions, and, of course, the individual natural thermal regulation of the body. The wind chill factor is also calculated according to the presumption that the temperature is at sea level. However, the air at altitude is significantly thinner, which lowers the heat capacity and also means that the wind chill is less pronounced.

How is wind chill calculated?

The current valid formula for calculating the wind chill factor is:

In which Ta represents the air temperature in Celsius and v is the wind speed in km/h. Therefore the formula does not apply in completely still conditions, since wind speeds under 1.34 m/s would result in the calculation of a positive wind chill factor. This has to with the insulating effect of the layer of air next to the skin, which remains warm in still conditions and is not displaced. This means that the formula only starts being valid at a wind speed of 5 km/h.

Wind chill vs. apparent temperature

The wind chill factor is frequently compared with the apparent temperature. However, the latter is calculated using different parameters, for example the humidity is taken into account with very high temperatures in the heat index. In addition to this, every person has a different level of heat sensitivity, which is determined by background, weight, size, fitness level, clothing, sun and skin characteristics, as well as other factors. Lastly, wind chill is also one of these factors.

Wind chill induced hypothermia

As previously mentioned, in positive temperatures the wind chill factor does not lead to frostbite. However it can lead to hypothermia. This begins when the body temperature falls below 35°C and then becomes apparent through shivering, palpitations and rapid breathing. If the body temperature falls further, this can lead to a clouding of consciousness, sinking blood pressure and heart rate, and in severe cases (body temperature below 28°C) can cause loss of consciousness, diminished brain activity, cardiac arrhythmia and finally death.

There are numerous factors which can cause hypothermia. These include low air temperatures, but the most dangerous instigators of rapid heat loss are cold water and wind (wind chill). In practical terms these factors can be caused by avalanches, breaks in the ice, long stays in cold environments with inappropriate clothing, as well as during physical over-exertion.

The treatment of hypothermia should be handed over to a doctor if possible. If no medic is available, then the affected person should be warmed up slowly. If the extremities are warmed up before the torso, the cold blood from these regions can be pumped to the heart, and this can lead to a further reduction in body temperature. This can also occur, when the extremities are placed higher up than the torso.

The following measures can be taken:

• Cover the person in warm dry clothing or blankets, making sure to also cover the head and neck.
• If possible give warm broth and food – no alcohol, or drugs, and no hot drinks or warm food, no coffee or black tea.
• If the victim is unconscious, the clothing should be removed with scissors and then the torso should be slowly warmed.

The best way to avoid hypothermia is to dress appropriately for the conditions. Windproof and waterproof clothing can be life saving in extreme situations. You should be careful to stay dry and not stand in the wind. Keep the head and mouth covered, so as not to lose too much warmth and not to flood the lungs with cold air.

Frostbite in very cold temperatures

In contrast to hypothermia, which only affects the circulation, frostbite affects the skin directly. It results from prolonged exposure and inadequate clothing in sub-zero temperatures and produces damage to blood vessels and cells, and finally necrosis – areas of dead skin.

Frostbite is divided into four degrees:

1. Degree: Pale skin, swelling of the affected skin areas, pain
2. Degree: Blue-red skin colour, blistering
3. Degree: Almost painless numbing of the skin
4. Degree: Freezing and complete skin death

Superficial frostbite can be treated by warming the affected areas of the body with body heat (e.g. placing hands under arms). In order to stimulate the circulation, the extremities should be kept moving and the body should be warmed up again with blankets and clothing. Warm, sweetened beverages can assist here. Blisters should not be broken and wounds should be covered with sterile dressings.

However, in more serious cases of frostbite the frozen areas of the body should not be warmed or moved. The most vulnerable areas are the outer extremities like the hands, feet, fingers and toes, as well as the prominent parts of the body like the nose, ears and chin.