Often, simply learning the expected high and low temperatures isn’t adequate preparation for going outdoors. Many people wait to hear the feels like temperature before they plan what to wear and where to go on any given day. This temperature gives people an idea about how they will feel outdoors, rather than a simple temperature that leaves them guessing. To determine this temperature, meteorologists must take into account factors like the wind chill and the heat index.
The feels like temperature is often determined in part by the wind chill during the winter months. Wind chill involves measuring the temperature as it is felt on the skin, which is determined by the air temperature and wind speed. In other words, it's a measure of the heat skin loses when the wind blows on it. The wind chill is typically always lower than the temperature of the air because wind increases how quickly moisture evaporates from the skin and serves to move heat away from the body. At higher temperatures, wind chill is considered far less significant and is usually not reported.
The heat index takes into account both the air temperature and the humidity in determining how warm temperatures feel to a person outdoors. When an individual perspires, the water in his or her sweat evaporates. This helps cool the body because heat is carried away during evaporation. When humidity is high, sweat cannot evaporate as easily, so people have a harder time cooling off, resulting in a higher heat index.
People should keep in mind that the feels like temperature they hear when listening to a local weather forecast may not be enough to determine how each individual will feel in certain weather. For example, heat index measurements are given for shady conditions with light wind evident. In full sunshine, the temperature may seem hotter than the heat index indicates. By the same token, if someone is standing in a sheltered area that receives full sun in winter, he or she may feel a bit warmer than the estimated wind chill.
The feels like temperature is particularly important for health reasons. When the heat index is very high, people may be at increased risk for heat exhaustion and heat stroke. Likewise, extreme wind chill temperatures can put people at risk for frostbite and hypothermia. As such, it is important for people to pay attention to these numbers in addition to the actual forecast temperature for the day.