High humidity can make people feel colder than they would otherwise.
Many people notice that hot, humid days feel much hotter than days with dry heat. One of the reasons for this is humidity, the amount of water that the air contains. When air holds more water, the basic act of perspiring or sweating is less effective at cooling the body. More water in the air means less water can evaporate from the skin, and most people will end up feeling warmer. Some of the ways to measure humidity are by measuring absolute humidity and relative humidity, which is usually how people say that one day it will be “humid”.
When meteorologists discuss relative humidity, they usually do so in percentages.
First, it’s important to understand that air can only hold so much water at any given time. This measurement is absolute humidity, and absolute humidity depends on the air temperature. In many circumstances, real air holds much less water than it technically could, so the relative term comes into play. When meteorologists discuss relative humidity, they usually do so in percentage amounts, and that percentage is a ratio of how much water the air holds compared to how much water it can hold. The actual formula is the amount of water (actual vapor density) divided by the total amount of water possible (saturation vapor density) times 100%. Most people will see this formula often expressed in relative humidity counts when watching or reading weather reports.
Relative humidity is determined by the amount of moisture in the air versus the amount of air it is able to maintain at that specific temperature.
That percentage or a day’s relative humidity can tell people how warm they can feel under certain circumstances. Dryer air may not feel as warm at higher temperatures. Air with about 45% relative humidity will be more like the outside temperature. Anything above that level can make the day feel hotter than it actually is at certain temperatures.
Sweating is less efficient at cooling the body on humid days.
Temperature perception can be affected by relative humidity in reverse. On cold days, usually below 53 degrees F (11.67 degrees C), the higher humidity can actually make people feel colder than they normally would. While other determinants such as wind chill can affect “temperature feel” and perception, relative humidity in cold weather can also be an important factor. Freezing weather with a relative humidity close to 100% can be much colder than freezing weather with a lower humidity level.
Measuring relative humidity cannot be the only determination of what the weather will be like; the amount of wind, especially in cooler temperatures and other factors come into play. In addition, individuals may be more or less sensitive to certain temperatures. However, it’s a good way to determine how hot or cold a day might feel.