7.5.6: Marine (Humid) West Coast Climate

Figure \(\PageIndex{1}\): Coastal Oregon, USA (Source: NOAA)

Geographical Distribution

The marine west coast climate, class Cfb and Cfc, is found along a relatively narrow strip of coastal Oregon, Washington, British Columbia, and southern Alaska in North America. It is likewise found along coastal Chile in South America. The marine west coast climate extends further inland into northwest Europe than in North America due to the orientation of mountains. This climate is also found on the southeast coast of Australia and New Zealand.

Distinguishing Characteristics

Temperature

The marine west coast is noted for its mild summers and winters and, as a result, a small annual temperature range. Its location on the west coast of a continent in the midlatitudes places the climate in the path of the Westerlies. In this situation, the climate receives a constant influx of oceanic air throughout the year. The mild temperatures are a direct result of the moderating influence of ocean bodies on air temperatures. The is especially true for those situations where a warm ocean current borders the continent, like the North Atlantic Drift's effect on northwestern Europe. Temperature ranges increase as one moves away from the coast.

Precipitation

Not only is the marine west coast noted for its mild temperatures but also for its heavy cloud cover and high humidity through much of the year. This is especially true for the marine west coast climate of North America where orographic uplift is an important climate control. Maritime polar air masses forced to rise up the windward, western slope create significant cloud cover and precipitation. The marine west coast climate is dominated by cyclonic activity embedded in the Westerlies. Frequent cyclonic storms bring prolonged periods of rain, drizzle and fog to these west coast locations. In some locations it is not uncommon to receive as much as 2540 mm (100 in) of precipitation in a year, an amount that rivals the rainy tropics.