What Is The Average Humidity In Seattle?

Seattle is known for its mild climate with damp, overcast weather for much of the year. But what are normal humidity levels throughout the seasons in the Emerald City? This article will examine Seattle’s average relative humidity percentages and patterns throughout the year.

If you’re short on time, here’s a quick answer to your question: Seattle sees an average annual relative humidity of around 75%. Summer is the least humid season, with average humidity dipping to 60-70%. Fall and winter are the most humid at 80-90%.

Overview of Seattle’s Average Humidity

Seattle, known for its renowned rainy reputation, experiences a unique climate that is heavily influenced by its proximity to the Pacific Ocean. As a result, the average humidity levels in Seattle tend to be higher compared to many other cities in the United States.

75% Annual Average

On average, Seattle has a humidity level of around 75% throughout the year. This means that the air in Seattle is often quite moist, creating a humid and sometimes muggy atmosphere. The high humidity can be attributed to the abundant rainfall and the oceanic moisture that gets carried inland by prevailing winds.

According to the National Weather Service, Seattle experiences an average annual rainfall of approximately 38 inches, with most of it occurring during the fall and winter months.

Seasonal Variations

While the average humidity remains relatively consistent throughout the year, there are noticeable seasonal variations. During the winter months, the humidity tends to be slightly higher, reaching around 80%, due to the combination of colder temperatures and increased precipitation.

In contrast, the summer months bring slightly lower humidity levels, averaging around 70%. This is often attributed to the warmer temperatures and the drying effect of the sun, which helps to evaporate moisture from the air.

Morning and Evening Peaks

Seattle experiences distinct peaks of humidity during the mornings and evenings. As the day begins, the humidity levels tend to be higher, gradually decreasing as the day progresses. This pattern is a result of the cooler temperatures during the night, which allow moisture to condense and increase humidity levels.

If you’re planning any outdoor activities in Seattle, it’s worth noting that mornings and evenings may feel more humid compared to the middle of the day.

Summer Humidity in Seattle

June Through August

Summer in Seattle is known for its mild temperatures and relatively low humidity compared to other parts of the country. However, that doesn’t mean it’s completely devoid of moisture. The average humidity in Seattle during the summer months of June through August typically ranges from 50% to 70%.

This means that while it may not feel as sticky or oppressive as some other regions, there is still a noticeable level of moisture in the air.

Cooler Temps, Less Rain

One of the reasons why the humidity in Seattle during the summer is not as high as in other parts of the country is due to the cooler temperatures. Seattle’s average high temperature during the summer months hovers around the mid-70s (°F), which is relatively mild compared to places like the southern United States.

Additionally, Seattle experiences less rainfall during the summer months, which can help keep the humidity levels in check.

Overnight Marine Layer Effect

Another factor that contributes to the humidity in Seattle during the summer is the overnight marine layer effect. As the cool marine air from the Pacific Ocean moves inland, it can create a layer of moisture that hangs over the city during the early morning hours.

This can lead to higher humidity levels until the sun rises and burns off the marine layer. However, once the marine layer dissipates, the humidity tends to decrease throughout the day.

It’s important to note that while the average humidity in Seattle during the summer is relatively moderate, there can still be variations from day to day. Weather patterns, such as the presence of high or low-pressure systems, can influence the humidity levels on any given day.

Therefore, it’s always a good idea to check the local weather forecast for the most accurate and up-to-date information.

For more information on Seattle’s climate and weather patterns, you can visit the Weather.com website.

Fall and Winter Humidity Levels

Seattle is known for its notoriously damp and rainy weather, and this is especially true during the fall and winter months. During this time, the humidity levels in the city can be quite high, leading to a sense of dampness and moisture in the air.

Wet Season Spikes

During the wet season, which typically lasts from October to April, Seattle experiences spikes in humidity levels. This is due to the combination of rain showers, overcast skies, and the proximity to bodies of water such as Puget Sound and Lake Washington.

These factors contribute to the high levels of moisture in the air, creating a humid environment.

80-90% Average Humidity

On average, the humidity in Seattle during the fall and winter months ranges from 80% to 90%. This means that the air is often saturated with moisture, making it feel damp and sticky. It’s not uncommon for residents to experience frizzy hair, foggy windows, and a general feeling of dampness during this time of year.

According to the National Weather Service, the average humidity in Seattle during the wet season is around 85%. This is significantly higher than the national average humidity of 60%.

Humidity Fluctuations

While the average humidity in Seattle during the fall and winter months remains relatively high, there are fluctuations in humidity levels throughout the season. Some days may see humidity levels reach as high as 95%, while others may be slightly lower, around 70-75%.

These fluctuations are influenced by various weather patterns, including rain showers, wind direction, and temperature changes.

It’s important to note that high humidity levels can have an impact on people’s daily lives. It can affect comfort levels, make it harder to dry laundry, and even contribute to the growth of mold and mildew in homes.

It’s recommended to use dehumidifiers and proper ventilation to maintain a comfortable indoor environment during the wet season.

For more information on Seattle’s weather patterns and average humidity levels, you can visit the Weather Channel’s website.

Spring Humidity and Rain Transitions

As spring arrives in Seattle, the city experiences a transition in humidity and rainfall patterns. The cool and damp conditions of winter gradually give way to warmer and drier weather. This transition is influenced by various factors, including changes in atmospheric pressure, wind patterns, and temperature.

Gradual Warming and Drying

During the spring months, Seattle experiences a gradual increase in temperature and a decrease in humidity. As the winter chill subsides, the air becomes milder and less saturated with moisture. This change in weather conditions brings relief to those who prefer drier climates and marks the beginning of outdoor activities and events in the city.

According to The Weather Channel, the average humidity in Seattle during spring ranges from around 60% to 70%. However, it is important to note that humidity levels can vary throughout the season and from year to year.

Factors such as rainfall and proximity to bodies of water can influence humidity levels in specific areas of the city.

April is the Wettest Month

While the overall trend in spring is towards drier conditions, April stands out as the wettest month in Seattle. Showers and rainfall are more frequent during this time, contributing to increased humidity levels.

Despite the rain, the city begins to see longer stretches of sunny days and warmer temperatures, making it an ideal time to explore Seattle’s parks, gardens, and outdoor attractions.

According to historical weather data from AccuWeather, the average rainfall in Seattle during April is around 2.5 inches. This precipitation, combined with the mild temperatures, creates an environment that promotes the growth of lush vegetation and colorful spring blooms.

Thunderstorms Possible

Another weather phenomenon that can occur during the transition to spring in Seattle is thunderstorms. As warm and moist air masses collide with cooler air, atmospheric instability can lead to the development of thunderstorms.

These storms can bring heavy rain, thunder, lightning, and gusty winds to the area.

While thunderstorms are not as common in Seattle compared to other parts of the country, they do occur from time to time during the spring months. It is advisable to stay informed about weather forecasts and take necessary precautions if thunderstorms are predicted.

How Seattle’s Humidity Compares to Other Cities

When it comes to humidity, Seattle has its own unique climate that sets it apart from other cities. Let’s take a closer look at how Seattle’s humidity compares to other major cities across the United States.

Higher Than Los Angeles

Contrary to popular belief, Seattle’s humidity is generally higher than that of Los Angeles. While Los Angeles is known for its dry and arid climate, Seattle experiences a more moderate level of humidity.

This can be attributed to its proximity to the Pacific Ocean, which brings moisture into the region.

Lower Than Miami

On the other hand, Seattle’s humidity is significantly lower than that of Miami. Miami’s tropical climate creates a hot and humid environment year-round, with high levels of moisture in the air. In comparison, Seattle’s humidity levels are relatively more moderate, making it more comfortable for residents and visitors.

Moderate Swings Unlike Southeast

While Seattle’s humidity can vary throughout the year, it generally experiences more moderate swings compared to cities in the Southeastern United States. Cities like Atlanta and Houston often face high humidity levels, especially during the summer months.

In contrast, Seattle’s humidity tends to remain within a moderate range, making it a more pleasant climate for many.


With an average annual humidity around 75%, Seattle sees seasonal variations peaking in fall and winter during the rainy season. But overall, the city maintains relatively moderate humidity levels year-round compared to many other parts of the country.

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