The climate in the United States varies with geographic location.
Each climate zone has distinct characteristics that are bound to affect the conditions in our homes, so having an idea of what the conditions are in your area can be a great way to predict how comfortable you’ll feel indoors.
The average home humidity levels vary across climate zones. In the southwest climate zone, Arizona has the lowest annual relative humidity of 53% in the morning and 25% in the afternoon. In the south climate zone, Mississippi has the highest recorded relative humidity of 91% in the morning.
Keep reading to learn how climate affects home humidity levels and each state’s exact relative humidity levels.
I’ll also cover ways to reduce the humidity in your home for better respiratory health and the protection of your home’s structure.
Let’s get started.
To discover the ideal home humidity for comfort and efficiency, read our article on the topic here.
Climate is arguably the single most significant factor dictating home humidity levels.
If the climate in your area is extremely humid, you can expect the humidity levels in your home to be high. The other way around is true, too.
The humidity of air is influenced by changes in temperature, air pressure, and water content. The dew point is an important measure that helps us understand the interaction of these different factors.
The dew point is the temperature at which the air is holding the maximum amount of water, for a given water content and air pressure, and cannot absorb any more.
The higher the air moisture level, the higher the dew point. At temperatures below the dew point, dew droplets will form from the excess moisture.
This is the phenomenon you can see when condensation forms on a cold window or mirror in the bathroom.
The amount of moisture in the air affects your comfort level. Air that is too dry or too humid will feel less comfortable than air in the optimal range of moisture content.
The dew point can be used to help predict how comfortable (or not) the atmosphere will feel, as follows.
- Dry and comfortable: dew points of less than 55°F
- Less comfortable and increased sticky feel to the air: dew points of 55-65°F
- The moisture in the air feels uncomfortable and oppressive: dew points above 65°F
The more humidity (a higher dew point) in your outdoor environment, the more humidity can enter your home.
In areas of the U.S. where the humidity remains high most of the year, a heating and air conditioning system has to work doubly hard to remove the water from the indoor air.
The relationship between temperature and humidity is easier to understand than dew point and humidity.
Everything else being equal, the higher the temperatures in any environment, the lower the relative humidity. The reverse holds true for cooler air; it has higher relative humidity.
Notice that when we’re referring to relative humidity and not absolute humidity.
Absolute humidity doesn’t consider temperature changes. It only measures the amount of water vapor in the air regardless of the air temperature.
This measure wouldn’t be useful in the context of today’s discussion since temperature changes in the environment strongly influence humidity levels in our homes.
Having established that the relative humidity levels in your climate zone dictate how humid your indoor air is, let’s take a look at the various climate zones to help you determine whether humidity may be an issue where you live.
Here’s a table showing the average humidity levels in various climate zones:
|Climate Zone||Description||Average Annual Relative Humidity Levels in Each State During Morning Hours (%)||Average Annual Relative Humidity Levels in Each State in the Afternoon (%)|
|Northwest Coastal Climate Zone||The average humidity level is low. The weather is often cool and humid or warm and dry.||Idaho: 68|
|West Climate Zone||The West climate zone experiences little humidity with a temperate climate for most of the year.||California: 76|
|Southwest Climate Zone||This climate zone tends to be very dry with little humidity.||Arizona: 53|
New Mexico: 60
New Mexico: 29
|The Northern Rockies and Plains Climate Zone||This area generally enjoys a continental climate of warm summers, cold winters, low humidity, and above-average precipitation.||Montana: 71|
North Dakota: 80
South Dakota: 83
North Dakota: 51
South Dakota: 53
|Upper Midwest Climate Zone||The Upper Midwest has a humid continental climate. They have hot days, cold waves, blizzards, floods, droughts, and tornadoes.||Iowa: 78|
|Ohio Valley Climate Zone||With the rivers and lakes in the Ohio Valley, the humidity is high. This area also gets moist air from the Gulf of Mexico to give it a humid continental climate, with some regions having humid and subtropical temperatures.||Illinois: 83|
West Virginia: 83
Missouri: 53Ohio: 57
West Virginia: 59
|Northeast Climate Zone||Many states in the Northeast climate zone experience warm air from the nearby waters with high-pressure fronts holding the steamy air in place.||Connecticut: 79|
Maine: 82 Maryland: 77
New Hampshire: 84
New Jersey: 83
New York: 82
Rhode Island: 78
New Hampshire: 53
New Jersey: 59
New York: 61
Rhode Island: 57
|South Climate Zone||The warm air of the South climate zone holds more moisture and feels very sticky. The high dew point contributes to the humid feel of the air.||Arkansas: 85|
|Southeast Climate Zone||The Southeast zone experiences more thunderstorms and rain due to its proximity to the Atlantic Ocean and the Gulf of Mexico. The long, hot summers and temperate winters mean the moisture stays in the air for much of the year.||Alabama: 84 Florida: 87|
North Carolina: 83
South Carolina: 86
North Carolina: 52
South Carolina: 49 Virginia: 52
The Pacific Northwest coastal region includes Idaho, Oregon, and Washington state. They have a marine oceanic climate characterized by cool winters and summers.
The warmest month reaches the low 70’s °F (20-25°C), and the coolest month averages a low of 27 to 32°F (-3 to 0°C).
Residents experience rain and other precipitation throughout the year with little to no dry season. They also encounter extended periods of rain and ongoing cloudy days.
California and Nevada comprise the West climate region.
The climate here is semi-arid, with rain only experienced from mid-November to mid-April and rarely during the other months.
The winters are mild, and the summers are pleasant, except where there are deserts that are hot in summer.
In the Southwest climate zone, much of the area consists of rocks and canyons.
This arid region of Arizona, Colorado, New Mexico, and Utah receives little rainfall and often sits on the verge of drought.
Many of these areas rely on melting mountain snowpacks to bring water for municipal uses.
This climate zone includes Montana, North Dakota, South Dakota, Nebraska, and Wyoming.
Seasonal storms bring floods to this part of the US, which supplies much of the nation’s agricultural lands.
These states are very wet in the spring and early summer and quite dry in winter.
Iowa, Michigan, Minnesota, and Wisconsin form the Upper Midwest climate zone, where the summers are hot, and the winters are freezing.
This area can be humid with extreme temperature swings in the four seasons.
The Ohio Valley climate zone focuses on the Ohio River and its surrounding areas.
Within the Ohio Valley zone of Illinois, Indiana, Kentucky, Missouri, Ohio, Tennesse, and West Virginia, there are humid, sub-tropical areas of hot, humid summers and mild winters.
The many lakes and rivers of the Ohio Valley create an ideal environment for grape growing.
The Ohio Valley zone’s humid summers come from airflow off the Gulf of Mexico, bringing a high dewpoint within the valley.
The Northeast climate zone encompasses Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, Vermont, New Jersey, New York, Pennsylvania, and Rhode Island.
This climate zone is wet, warm, and humid in the summer and snowy and cold in winter.
June, July, and August are especially warm and muggy.
Arkansas, Louisiana, Kansas, Mississippi, Oklahoma, and Texas form the South climate zone.
The climate here is subtropical, with much of the year being warm or hot with mild winters.
The frequent summer thunderstorms and tropical storms like hurricanes in July, August, and September keep the humidity high.
The direct connection with the Atlantic Ocean and the Gulf of Mexico strongly influences the climate in the Southeast climate zone of Alabama, Florida, Georgia, South Carolina, North Carolina, and Virginia.
Although most of these states fall in a warm, temperate zone, there is marked variation among the weather characteristics.
The hurricane season of June, July, August, and September brings intense storms with hot, humid conditions.
The southern tip of Florida has a tropical savanna climate, while the rest of the state is subtropical.
Your home will feel comfortable with a 30-50% humidity level.
Your HVAC system should control the home humidity, but you might need a home humidifier to improve the comfort level if the relative humidity in your area is extremely high.
Here are some indicators that your home humidity is high:
- Foggy windows.
- The indoor air feels clammy and uncomfortable.
- Mold around the ceiling air vents or on the wall.
- Rotten wood.
- You find it difficult to breathe, and your nose is stuffy when you are inside.
- Your home has a mildew smell.
Reducing the humidity levels in your home can preserve the walls and woodwork and improve your respiratory health.
Here are some ways to reduce the amount of water vapor in your home when you live in a high-humidity zone:
- Have your air conditioning checked if it is not correctly drawing moisture out of the air.
- Use the exhaust fans in the bathrooms during every shower.
- Turn on the vent fan to remove the hot air over the stove when cooking.
- Check your home for leaky pipes that can add moisture to the indoor air.
- Use a home dehumidifier to reduce moisture levels.
Home humidity levels affect how well you sleep, your ease of breathing, and any allergy problems you might have.
When you live in an area with high humidity, this moisture can seep into your home to increase the humidity.
Taking action to keep your home in the 30 to 50% humidity range will improve indoor comfort.
For information about how to reduce the humidity in your home without using a dehumidifier, read our article on the subject, “Lower Humidity in 14 Ways (With No Dehumidifier Required).”