Rainfall patterns across the United States vary significantly, prompting curiosity about which specific urban area receives the highest amount of precipitation annually. This exploration aims to pinpoint the US city with the most substantial rainfall, providing context on how precipitation is measured and the atmospheric conditions that contribute to such distinctions.
The City with the Most Rain
Ketchikan, Alaska, is the United States city with the highest average annual rainfall. Located in the southeastern part of the state, this coastal community receives an average of 141 to 149.6 inches of precipitation each year. This substantial amount makes Ketchikan significantly wetter than any city in the contiguous United States. The city’s geographic position along the Inside Passage contributes to its consistently high precipitation levels. While other US cities also record high precipitation, Ketchikan’s consistent and abundant rainfall sets it apart as the nation’s wettest urban center.
How We Measure Rainfall
Rainfall is primarily measured as total annual precipitation, which quantifies the accumulated liquid equivalent of all forms of precipitation, including rain, snow, sleet, and hail, over a year. This metric is distinct from “rainy days,” which simply counts days with any measurable precipitation. A city might have many rainy days but less total rainfall than an area with fewer, heavier downpours.
Weather stations employ specialized instruments, such as rain gauges, to collect and measure precipitation accurately. To ensure reliable and comparable data, meteorologists and climate scientists typically rely on long-term averages, often spanning 30 years. These 30-year “normals” provide a stable baseline for understanding a region’s typical climate patterns and for making meaningful comparisons between different locations.
Why Some Cities Get More Rain
Several atmospheric and geographical factors combine to create regions of high rainfall. One significant factor is the presence of large bodies of water, which act as sources of moisture for the atmosphere. Warm ocean waters, for example, lead to high evaporation rates, releasing substantial amounts of water vapor into the air. This moist air can then be carried over land by prevailing wind patterns.
When this moisture-laden air encounters elevated terrain, such as mountains, it is forced to rise. As the air ascends, it cools, causing the water vapor to condense into clouds and precipitate as rain or snow. This phenomenon is known as orographic lift. Hilo, Hawaii, for example, experiences high rainfall partly due to its location on the windward side of large volcanoes, where moist trade winds are forced upwards.
Additionally, persistent storm tracks can funnel weather systems repeatedly over certain areas, leading to increased precipitation. Coastal regions, particularly those adjacent to warm ocean currents, are often prone to frequent storm development and heavy rainfall.
Other Major US Rain Centers
Beyond the absolute rainiest city, several other regions in the United States are known for significant annual rainfall. The Gulf Coast, encompassing cities like Mobile, Alabama, and New Orleans, Louisiana, consistently receives high precipitation. This is largely due to the warm, moist air from the Gulf of Mexico, coupled with frequent thunderstorms and the influence of tropical systems.
The Pacific Northwest, including cities like Seattle, Washington, and Portland, Oregon, is often associated with frequent rain, though its total annual accumulation can be less than that of some Gulf Coast cities. Here, moist air from the Pacific Ocean brings consistent, often lighter, rainfall, particularly during the cooler months. Furthermore, some cities near the Great Lakes, such as Syracuse, New York, experience substantial precipitation, including heavy snowfall, due to the “lake effect” where cold air picks up moisture and warmth from the relatively warmer lake waters.