The question of which area in the United States receives the most rain is answered by looking at specific microclimates where extreme conditions exist, rather than simple state averages. “Rain” refers to total liquid precipitation, including rainfall and the water equivalent of snow, measured over an average annual cycle. Identifying the wettest location requires differentiating between the contiguous United States and non-contiguous states, as island and coastal mountain geography creates highly localized precipitation extremes. The total volume of water accumulated each year is the definitive metric used.
The Areas Receiving the Highest Annual Precipitation
The undisputed holder of the highest average annual precipitation in the United States is Mount Waialeale, located high on the island of Kauai, outside the contiguous 48 states. It receives an average of approximately 450 inches of precipitation each year, placing it among the wettest spots on the planet. This total is achieved because the mountain’s peak directly intercepts prevailing trade winds, squeezing moisture from the air constantly.
The second-wettest region is the southeastern Alaska Panhandle, characterized by a temperate rainforest climate. Little Port Walter, a research station on Baranof Island, records an average annual precipitation total of around 246 inches. These totals result from a combination of heavy rainfall and significant snowfall, measured by the liquid equivalent of the frozen precipitation.
When focusing only on the contiguous United States, the record totals are found in mountainous coastal areas, though they are significantly lower than in Hawaii or Alaska. The Pacific Northwest holds the top spots, with remote sites in Washington’s Olympic Mountains and the Cascade Range receiving substantial precipitation. Locations like June Lake in Washington have averaged totals approaching 167 inches per year.
The Gulf Coast also contributes to the nation’s highest totals due to its proximity to warm, moisture-rich waters. Cities like Mobile, Alabama, and New Orleans, Louisiana, typically receive annual precipitation totals in the range of 60 to 66 inches. These figures represent a pattern of heavy, frequent downpours concentrated in the summer and fall, differing from the year-round saturation of the Pacific mountain ranges.
How Geography Shapes Extreme Rainfall
Orographic lift is the primary driver behind the most extreme precipitation totals in the US. This phenomenon occurs when a moisture-laden air mass encounters a mountain barrier and is forced upward to a higher elevation. As the air rises, it expands and cools, causing the water vapor within it to condense rapidly into clouds and precipitation.
The height and orientation of a mountain range determine how effectively it can “wring” moisture out of the atmosphere. The steep, windward slopes of Mount Waialeale in Hawaii, for example, create an intense, localized lift that causes near-constant rainfall. Conversely, the air descending the opposite side of the mountain is dry, leading to a “rain shadow” effect where annual totals can drop to only a few inches a short distance away.
In the Pacific Northwest and California, intense precipitation is often fueled by atmospheric rivers, which are long, narrow corridors of concentrated moisture transport. These channels, sometimes referred to as the “Pineapple Express,” carry water vapor thousands of miles from the tropical Pacific Ocean toward the West Coast. When these rivers collide with coastal mountain ranges, the resulting orographic lift unleashes days of heavy, continuous rain and snow.
High precipitation totals along the Gulf Coast and Eastern Seaboard are driven by a constant supply of warm, humid air from the Gulf of Mexico and the Atlantic Ocean. This moisture feeds powerful thunderstorms, tropical cyclones, and extratropical storms that track up the coast. These systems lead to intense rainfall events across the Southeast and Mid-Atlantic states.
Volume Versus Frequency: Defining the “Wettest”
The definition of “wettest” hinges entirely on the total accumulated volume of precipitation, measured in inches or millimeters. This metric provides a clear, quantitative measure of the amount of water delivered to a location over a period, typically a year. However, this metric does not account for the number of days on which precipitation actually falls.
Some northern cities, particularly those near the Great Lakes, have a high frequency of precipitation days but a lower overall volume. Cities like Syracuse, New York, and Seattle, Washington, often rank high in the number of days with measurable rain or snow. These areas may see precipitation on 150 to 170 days a year, but the events are often light, resulting in moderate annual totals.
In contrast, the “wettest” spots, like those in Hawaii and Alaska, achieve their record totals through a combination of high frequency and high intensity. While Mount Waialeale experiences hundreds of rainy days, the volume of water that falls during each event is far greater than what is seen in the Great Lakes region. Therefore, while frequency describes the persistence of precipitation, volume remains the established standard for designating the nation’s rainiest locations.