91Æƽâ°æ

The summer of 2023 has been the hottest on record — and it’s not over yet. In some of the most humid states in the U.S., the heat has been accompanied by excessive humidity, making for a suffocating, soupy summer.

Relative humidity is a key metric in calculating the heat index — the measure of what the temperature feels like to the human body. High temperatures combined with high relative humidity make for some of the most unbearable conditions, while high temperatures and low relative humidity can mean a more tolerable experience (so long as air temperatures remain within a reasonable range).

So where can you go to escape the excessive humidity that makes summer heat so uncomfortable? We analyzed annual humidity records for more than 250 cities to find the most and least humid states and cities in the US.

Key findings

• It’s a dry heat… Arizona is the least humid state in the US, with an average annual relative humidity of just 40.4%, while Alaska is the most humid state in the US, with an average relative humidity of 74.3%.
• The majority of the least humid states are in the southwestern and western regions of the US, while the majority of the most humid states belong to the midwestern and southern regions.
• Arizona has the most cities with low relative humidity, with a total of three cities. California and New Mexico trail closely behind, with two cities each.
• Alaska has the highest number of cities with high relative humidity, at a whopping seven.

Top 10 most humid states

1. Alaska: 74.33%
2. Louisiana: 74.25%
3. Mississippi: 72.5%
4. Michigan: 72.19%
5. Florida: 72.17%
6. Minnesota: 71.90%
7. Iowa: 71.88%
8. Wisconsin: 71.63%
9. Illinois: 71% (tie)
10. Indiana: 71% (tie)

Top 10 least humid states

1. Arizona: 40.38%
2. Nevada: 44.10%
3. New Mexico 45.67%
4. Colorado: 49.10%
5. Utah: 53%
6. Wyoming: 54.75%
7. Idaho: 56%
8. California: 58.62%
9. Montana: 59.36%
10. Maryland: 65% (tie)
11. Rhode Island: 65% (tie)

Most humid cities

Least humid cities

What is an uncomfortable humidity level?

An uncomfortable humidity level often falls on either extreme of the spectrum. High humidity, typically above 60%, can make the air feel heavy and stifling, and impair the body's ability to cool down through evaporation. This can lead to discomfort, and the suffocating feeling sometimes reported in high-humidity climates, especially when coupled with high temperatures.

On the other hand, low humidity, usually below 30%, can result in dry air that leads to skin dryness, irritation, and respiratory discomfort. Striking a balance between these extremes — ideally maintaining indoor humidity between 30% and 50% — is essential for fostering a comfortable and healthful environment.

What is relative humidity?

Relative humidity (RH) is a measure of the amount of water vapor present in the air, compared to the maximum amount of water vapor that the air could hold. It is expressed as a percentage, representing how close the air is to being fully saturated with moisture at a given temperature.

Relative humidity is influenced by both the temperature and the amount of moisture in the air. Warmer air can hold more moisture before becoming saturated, while cooler air has a lower capacity for holding moisture. As air cools, its relative humidity may increase even if the actual amount of water vapor remains constant, potentially leading to the formation of dew or condensation.

How is relative humidity measured?

Relative humidity (RH) can be calculated using the following formula:

RH = (Actual Vapor Pressure / Saturation Vapor Pressure) X 100

Where:

• Actual Vapor Pressure is the pressure exerted by the water vapor in the air.
• Saturation Vapor Pressure is the pressure that the water vapor would exert if the air were fully saturated at the same temperature.

Today, digital hygrometers are commonly used to measure relative humidity. These devices use sensors to detect changes in electrical capacitance, resistance, or other properties that vary with humidity levels. They provide quick and accurate readings of relative humidity.

It's important to note that while relative humidity is a crucial measure, it doesn't give a complete picture of moisture content in the air. It's often used in conjunction with other measures like specific humidity and dew point to better understand atmospheric moisture conditions.

Humidity FAQs

Your questions about humidity, answered.

Can humidity affect my health?

Yes, both high and low humidity levels can impact health. High humidity can cause discomfort, heat-related illnesses, and worsen respiratory problems. Low humidity can lead to dry skin, respiratory discomfort, and irritation in the eyes. Maintaining indoor humidity between 30% and 50% is ideal for a healthy and comfortable environment.

How can I stay comfortable in humid conditions?

To ensure comfort in humid conditions, consider using indoor air conditioning or dehumidifiers to lower humidity levels. Stay well-hydrated by drinking ample water, and opt for lightweight, breathable clothing. Enhance air circulation by utilizing fans and cross-ventilation, and minimize outdoor activities during the hottest parts of the day.

How does humidity affect human comfort?

Humidity significantly impacts human comfort by altering our perception of temperature. In high humidity, sweat evaporation is hindered, leading to a sensation of increased warmth, even at moderate temperatures. Conversely, low humidity can cause moisture to evaporate from our skin more rapidly, leading to sensations of dryness and potential irritation.

Methodology

Relative humidity data came from the National Oceanic and Atmospheric Administration’s Comparative Climate Data database. 91Æƽâ°æ analyzed the annual morning and afternoon relative humidity levels of 257 cities for the period of record available, ranging from 1940 to 2018.