Humidity is the concentration of water vapor present in the air. Humidity is a byproduct of the water cycle; as water turns into its gaseous state, water vapor, it begins to fill the air. Atmospheric water vapor also plays an important role in the weather and climate, regulating air temperate by absorbing thermal radiation from the Sun and helping generate precipitation.
Local weathermen typically report relative humidity, a percentage representing the amount of water vapor in the air relative to the maximum amount the air can hold. Temperature determines the humidity capacity of air. As temperatures decrease, air molecules compress and can hold less water vapor. At higher temperatures, the air is capable of holding more water vapor.
Humidity levels affect how temperatures are perceived. Higher levels slow the evaporation of sweat and make it more difficult for bodies to regulate their temperatures, resulting in excessive sweating and increased heart rate and respiration. On the other hand, low humidity can dry skin and allow airborne illnesses to spread more quickly. Most people are the most comfortable at around 30-60% humidity.
Since humidity levels result from evaporation, they tend to be highest in regions near large bodies of water. Landlocked states with very few large bodies of water tend to be the least humid. States like Nevada, Arizona, Colorado, and New Mexico have relatively low humidity and arid climates. On the other hand, Florida and Louisiana have hot, humid climates due to their warm weather and proximity to the Atlantic.
However, because relative humidity has to do with how much water the air can hold at a specific temperature, rather than the amount of water actually in the air, relative humidity can be much higher in cold areas even though there is less overall moisture in the air. For this reason, Alaska tops the nation for relative humidity levels, despite having much lower absolute humidity than most states in the South.
New Orleans, Louisiana (75.9%) Jacksonville, Florida (75.8%) Houston, Texas (74.7%) Orlando, Florida (74.1%) Tampa, Florida (74.1%) San Francisco, California (73.7%) Seattle, Washington (73.3%) Miami, Florida (73.2%) Portland, Oregon (73.2%) Rochester, New York (72.6%)
Average Relative Humidity
Average Dew Point F