There are six factors that influence how a person will feel when going outside. They are sunlight, wind, evaporative cooling, temperature, humidity and clothing. The combination of these six factors determine whether a person feels cold, warm, comfortable, uncomfortable OR like the porridge in Goldilocks and the three bears "just right". Let's take a look at each of the six factors. Direct sunlight makes a person feel warmer because electromagnetic radiation is being embedded directly into the skin. If the temperature feels uncomfortably cool in the shade, standing in direct sunlight will make one feel warmer. Wind makes a person feel cooler especially when the wind is blowing over moistened skin. This effect is very apparent if you have gotten out of a swimming pool on a windy and dry day. The wind evaporates moisture from the body. Since evaporation is a cooling process and absorbs latent heat away from the body, the person feels colder. Skin always has moisture on it. Just like a tree transpires, the human body is constantly having water evaporated from it. Wind intensifies this process. A hot day with a breeze will feel more comfortable than a hot day with calm wind. Wind and evaporative cooling are closely linked. The higher the wind, the greater the amount of evaporative cooling, especially if air is dry. Perhaps the most important factor in determining comfort is temperature. If the temperatures are cold, the human body conducts energy to the surrounding air and gradually loses heat (you shiver and feel cold!). If temperatures are too warm, excess heat builds in the body and the body has trouble releasing that heat to the surrounding air (water loss rate from your skin increases from sweat and you feel hot!). The humidity is important because it determines the overall loss of water from your body. If the air is dry, the effect of evaporative cooling on the body is maximized. Evaporative cooling and a wind breeze can partially or completely offset temperatures that would normally be considered uncomfortably hot. When the humidity is high, the effect of evaporational cooling is reduced. Because of this, heat builds in the body. At the same temperature, a humid day will feel more warm and uncomfortable than a dry day. When the dewpoint climbs above 60 F, high humidity is noticeable. The last factor is clothing. Clothing can obviously make you feel comfortable on a day that is considered warm or cold. Clothes are added to counter the chill in the air. The wind chill value is only relevant to exposed skin. There are variables the wind chill index does not consider including direct sunlight and some assumptions in the wind chill equation do not mirror reality perfectly. On a cold day it is best to dress in layers. The goal is to maximize the heat between the skin and the clothes on a cold day. On a hot day, white clothes and loose fitting clothes are the best. Everyone has a slightly different temperature they consider being the "comfortable temperature". This range for any one person tends to be from 68 to 78 F. All the six factors mentioned go into determining how a person will feel. The combination of all these factors is so complex that no formula using all these factors has been developed. The two that are commonly used today are the wind chill and heat index. Wind chill considers wind and temperature while the heat index considers heat and humidity. These two indices do not take into account several other factors that determine how one will feel. The heat index does not consider wind and direct sunlight. In summary, if you feel cold you can step into the sunlight, reduce the wind, increase the temperature, increase the humidity, and increase clothing. If you feel hot, you can step out of direct sunlight, increase the wind, decrease the temperature, decrease the humidity and reduce clothing. Off course, we can not control all these variables that occur in the atmosphere except for three ways: (1) wear proper clothing (2) go inside to a comfortable building (3) evaporative cooling through adding water to the skin surface on a hot day. |