The Marine West Coast climate, often called the oceanic climate, is known for its consistent mild temperatures and abundant moisture throughout the year. This climate type contrasts sharply with regions experiencing extreme heat or cold, providing a more moderate environment. It typically occurs on the western sides of continents in the mid-latitudes, where oceanic influences are prominent.
Defining Characteristics
The Marine West Coast climate features mild temperatures year-round, lacking the severe hot or cold extremes found in many other climate types. Mean annual temperatures in lowland areas typically range from 7 to 13°C (45 to 55°F). Summers are generally cool, with monthly averages rarely exceeding 20°C (68°F), while winters remain mild, with the coldest month’s average temperature usually above 0°C (32°F). This results in a relatively small annual temperature range, often between 10-15°C (50-59°F).
Precipitation is a consistent feature of this climate, occurring throughout the year, though often with a winter maximum. Annual accumulations generally range from 50 to 250 cm (20 to 98 inches), but can exceed 500 cm (197 inches) in areas where moist onshore winds encounter mountain ranges. Rainfall is frequent, with many areas experiencing precipitation more than 150 days per year. Rather than heavy downpours, precipitation often manifests as prolonged periods of light rain, drizzle, and fog, contributing to high humidity and extensive cloud cover.
Humidity levels in Marine West Coast climates are consistently high, often around 80% or even higher, particularly during cooler months when cloud cover and fog are common. This high moisture content in the air contributes to the damp feel of these regions. Snowfall can occur in winter, but it is typically light and does not persist for long periods.
Global Distribution
The Marine West Coast climate is found primarily along the western coasts of continents in the mid-latitudes, typically between 35° and 60° North and South latitude. This climate often exists in a relatively narrow strip along these coastlines.
In North America, this climate extends from northern California through Oregon, Washington, and into British Columbia, Canada, and southern Alaska. Western Europe also widely experiences this climate, including the British Isles, coastal Norway, and parts of France, where it can extend further inland than on other continents. Southern Chile, along its coastal regions, is another significant area with this climate type.
Other notable locations include southeastern Australia and New Zealand, where the climate influences coastal areas. Smaller, isolated pockets of this climate can also be found in South Africa. The presence of mountains frequently restricts the inland expansion of this climate, confining it to coastal zones.
Influencing Factors
The existence and characteristics of the Marine West Coast climate are shaped by a combination of geographical and atmospheric elements. Proximity to large ocean bodies is a primary influence, as oceans warm and cool more slowly than land. This moderating effect prevents extreme temperature fluctuations, keeping coastal areas cooler in summer and warmer in winter.
Prevailing westerly winds, originating over the ocean between 30 and 60 degrees latitude, consistently carry moist air inland. These winds are a constant influx of oceanic air, bringing humidity and precipitation to the western continental margins.
Warm ocean currents, such as the North Atlantic Drift, further moderate winter temperatures in regions like northwestern Europe. While some western coasts, like those in North America, are influenced by cooler currents such as the California Current, the overall effect of ocean currents is to regulate temperature and maintain moisture levels.
Topography also plays a significant role, particularly the orographic effect. Coastal mountain ranges force the moist, incoming air to rise. As this air ascends, it cools, and its water vapor condenses, leading to cloud formation and substantial precipitation on the windward slopes. This process explains the high annual rainfall in many Marine West Coast regions. The frequent passage of mid-latitude cyclonic storms, especially during winter, also contributes significantly to the consistent precipitation, bringing prolonged periods of rain, drizzle, and fog.