Oceanic climate

An oceanic climate, also known as a marine climate or maritime climate, is the temperate climate sub-type in Köppen classification represented as Cfb or represented as Do under the Trewartha climate classification, typical of west coasts in higher middle latitudes of continents, generally featuring warm summers and cool to mild winters (for their latitude), with a relatively narrow annual temperature range and few extremes of temperature under Köppen's system or mediocre growing seasons with mild winters under Trewartha's. Oceanic climates can be found in both hemispheres generally between 40 and 60 degrees latitude, with subpolar versions extending to 70 degrees latitude in some coastal areas and some hot-summer oceanic climates extending to just north of 35 degrees North latitude in North America and Honshu and just south of 35 degrees North latitude in Mainland China under the Trewartha classification. Other varieties of climates usually classified together with these under the Köppen system include subtropical highland climates, represented as Cwb or Cfb, and subpolar oceanic or cold subtropical highland climates, represented as Cfc or Cwc. Subtropical highland climates occur in some mountainous parts of the subtropics or tropics, some of which have monsoon influence, while their cold variants and subpolar oceanic climates occur near polar or tundra regions.

Precipitation Locations with oceanic climates tend to feature frequent cloudy conditions with precipitation, low-hanging clouds, and frequent fronts and storms. Thunderstorms are normally few except in the hot-summer Doak variety seen under the Trewartha climate classification system, since strong daytime heating and hot and cold air masses meet infrequently in the regions, but are more common in subtropical highland climates where these air masses meet more frequently due to the influence of hotter weather in the subtropics or tropics, especially in monsoon-influenced climates. In most areas with an oceanic climate, precipitation comes in the form of rain for the majority of the year. Most oceanic climate zones, however, experience at least one snowfall per year. Snowfall is more frequent and commonplace in the subpolar oceanic climates due to the colder weather in those locations.

Temperature

Under the Köppen climate classification system Overall temperature characteristics of the oceanic climates feature cool temperatures and infrequent extremes of temperature. In the Köppen climate classification, oceanic climates have a mean temperature of 0 °C (32 °F) or higher (or −3 °C (27 °F) or higher) in the coldest month, compared to continental climates where the coldest month has a mean temperature of below 0 °C (32 °F) (or −3 °C (27 °F)). Summers are warm but not hot, with the warmest month having a mean temperature below 22 °C (72 °F). Poleward of the latter is a subtype of it, the subpolar oceanic climate (Köppen Cfc), with long but relatively mild (for their latitude) winters, and cool and short summers with average temperatures of at least 10 °C (50 °F) for one to three months. Examples in the Northern Hemisphere include parts of coastal Iceland, the coast of Norway north of Bodø, the mountains of Scotland, parts of Shetland, and the British Columbian coast in Canada. In the Southern Hemisphere, examples include extreme southern Chile and Argentina (such as Punta Arenas and Ushuaia), the Falkland Islands, parts of southeastern Australia, and much of New Zealand.

Under the Trewartha climate classification system Oceanic climates are defined very differently under the Trewartha climate classification system. In temperate areas, oceanic climates exist where four to seven months average at least 10 °C (50 °F) regardless of summer heat or lack thereof, so long as the coldest month averages at least 0 °C (32 °F). This allows some places with hot summers, such as New York City, the District of Columbia, and Louisville, Kentucky, to have oceanic climates under the Trewartha system, although these climates are considered humid subtropical under the Köppen system due to summer heat instead of the length of the growing season being the trigger for Köppen. In boreal/subpolar areas, Trewartha defines areas like Anchorage that have winters averaging over −10 °C (14 °F) as oceanic climates even if they are insufficiently mild to be classified as oceanic under Köppen too like Reykjavík is, as opposed to the freezing isotherm used in temperate climates. Nonetheless, Köppen and Trewartha concur on the summer temperature of a subpolar climate, with one to three months averaging over 10 °C (50 °F) being the trigger for both.

Cause

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