World map showing oceanic climate zones, as defined by the Köppen climate types "Cfb", "Cfc", "Cwb" and "Cwc"
An "oceanic climate" (also known as "marine", "west coast" and "maritime") is the climate typical of west coasts in higher middle latitudes of continents, and generally features cool summers and cool (but not cold) winters, with a relatively narrow annual temperature range and few extremes of temperature, with the exception for transitional areas to continental, subarctic or subtropical climates. Summers below 22 °C (72 °F) and winters above −3 °C (27 °F) in mean temperatures are eligible for the classification, resulting in significant differences of characteristics in terms of how the oceanic climate manifests. As a result, heavy snowfall occur in some northerly oceanic areas, especially in coastal Alaska.
It typically lacks a dry season, as precipitation is more evenly dispersed throughout the year. It is the predominant climate type across much of North Western Europe, the Pacific Northwest region of the USA and Canada, portions of southwestern South America and small areas of southeast Australia, and New Zealand as well as isolated locations elsewhere. On east coasts of continents, the transition from continental normally goes directly to subtropical due to greater influence from the interior.
Oceanic climates generally have cool to warm (but not hot) summers and mild to cool (but not cold) winters. They are characterized by a narrower annual range of temperatures than are encountered in other places at a comparable latitude, and generally do not have the extremely dry summers of Mediterranean climates or the hot summers of warm temperate climates. Oceanic climates are most dominant in Europe, where they spread much farther inland than in other continents.
Oceanic climates can have much storm activity as they are located in the belt of the stormy westerlies. Many oceanic climates have frequent cloudy or overcast conditions due to the near constant storms and lows tracking over or near them. The annual range of temperatures is smaller than typical climates at these latitudes due to the constant stable marine air masses that pass through oceanic climates, which lack both very warm and very cool fronts.
Precipitation is both adequate and reliable throughout the year in oceanic climates. Extended months of rain and cloudy conditions are common in oceanic climates. Seattle is an example of this. Between October and May, Seattle experiences high rainfall and is mostly or partly cloudy six out of every seven days.
In most areas with an oceanic climate, precipitation comes in the form of rain for the majority of the year. However, some areas with this climate see some snowfall annually during winter. Outside of Australia and parts of New Zealand, most areas with an oceanic climate experience at least one snowstorm per year. In the poleward locations of the oceanic climate zone ("subpolar oceanic climates," described in greater detail below), snowfall is more frequent and commonplace.
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 −3 °C (27 °F) or higher in the coldest month, compared to continental climates where the coldest month has a mean temperature of below −3 °C (27 °F). Summers are cool, with the warmest month having a mean temperature below 22 °C (72 °F). Poleward of the latter is a zone of the aforementioned subpolar oceanic climate (Köppen Cfc), with long but relatively mild winters and cool and short summers (average temperatures of at least 10 °C (50 °F) for one to three months). Examples of this climate include parts of coastal Iceland in the Northern Hemisphere and extreme southern Chile and Argentina in the Southern Hemisphere (examples include Ushuaia and Punta Arenas).
Oceanic climates are not necessarily always found in coastal locations on the aforementioned parallels; however, in most cases oceanic climates parallel higher middle latitude oceans. The polar jet stream which moves in a west to east direction across the middle latitudes, advancing low pressure systems, storms, and fronts. In coastal areas of the higher middle latitudes (45–60° latitude), the prevailing onshore flow creates the basic structure of most oceanic climates. Oceanic climates are a product and reflection of the ocean adjacent to them. In the fall, winter, and early spring, when the polar jet stream is most active, the frequent passing of marine weather systems creates the frequent fogs, cloudy skies, and light drizzle often associated with oceanic climates. In summer, high pressure often pushes the prevailing westerlies north of many oceanic climates, often creating a drier summer climate (for example in the Pacific Northwest of the USA and Canada).
The North Atlantic Gulf Stream, a tropical oceanic current that passes north of the Caribbean and up the East Coast of the USA to North Carolina, then heads east-northeast to the Azores, is thought to greatly modify the climate of Northwest Europe. As a result of the Gulf Stream, west-coast areas located in high latitudes like Ireland, the UK, and Norway have much milder winters (for their latitude) than they would otherwise have. The lowland attributes of western Europe also helps driving marine air masses into continental areas, rendering cities such as Dresden, Prague, and Vienna to have maritime climates in spite of being located well inland from the ocean.
Oceanic climates in Europe occur mostly in Northwest Europe, from Ireland and Great Britain eastward to central Europe. Most of France (away from the Mediterranean), Germany, Norway, the north coast of Spain and southern portions of Sweden, also have oceanic climates. Examples of oceanic climates are found in London, Bergen, Dublin, Berlin, Zürich, Copenhagen, Paris and Vigo. With decreasing distance to the Mediterranean Sea, the oceanic climate of Northwest Europe gradually changes to the subtropical dry-summer or the more humid subtropical climate of southern Europe. In transitional areas the oceanic climate can have extremely warm summer days, such as in Pamplona in northern interior Spain with summer highs of 28.3 °C (82.9 °F). The prevalence of such oceanic climates depend on how much the nights cool down and how prone the location is to summer drought. Southern Germany also sees very warm summers, especially around the Rhine shift in Baden-Württemberg, but with more reliable precipitation. Northern Germany sees a chillier variety more prone to frosts and cooler summers. The oceanic climates of especially coastal Green Spain, but also to a lesser degree the immediate French atlantic coastline, most of Ireland, South Wales, Devon and Cornwall in England's south west are heavily moderated during winters and with cooler summers than its latitudes would suggest.
The oceanic climate exists in an arc spreading across the north-western coast of North America from the Alaskan panhandle to northern California, in general the coastal areas of the Pacific Northwest. It includes the western parts of Washington and Oregon, the Alaskan panhandle, western portions of British Columbia, and north-western California. In addition, some east coast areas such as Block Island and Cape Cod have a similar climate. A significant portion of oceanic climate exhibited in North America features a drying trend in the summer, thus falling under the dry-summer subcategory explained below.
All mid-latitude oceanic climates are classified as humid. However, some rainshadow climates feature thermal régimes similar to those of oceanic climates but with steppe-like (BSk) or even desert-like (BWk) scarcity of precipitation. Despite the oceanic-like thermal regimes, these areas are generally classified as mild steppe or desert climates. This milder version of steppe and desert climates are found in Washington and Oregon to the east of the Cascade Range in the United States, Patagonia in southern Argentina, and the Atacama Desert in northern Chile.
The only noteworthy area of Maritime Climate at or near sea-level within Africa is in South Africa from Mossel Bay on the Western Cape coast to Plettenberg Bay, with additional pockets of this climate inland of the Eastern Cape and KwaZulu-Natal coast. Interior southern Africa and elevated portions of eastern Africa and Mozambique also share this climate type. It is usually warm most of the year with no pronounced rainy season, but slightly more rain in autumn and spring.
The only significant areas where this climate is found at or near sea level in Asia is on the Black Sea coast in northern Turkey, in small pockets along or near the Caspian Sea in Azerbaijan and in small pockets along or near the Tsugaru Strait in northern Japan.
The oceanic climate is prevalent in the more southerly locations of Oceania. A mild Maritime climate is in existence in New Zealand. In Australia, the island of Tasmania, southeastern New South Wales (starting from the Illawarra region) and the southern parts of Victoria, also exhibit a mild Maritime climate. It can also be found along the western areas of the south coast of Western Australia, parts with steppe-like (BSk) or even desert-like (BWk) scarcity of precipitation.
The subtropical highland variety of the oceanic climate exists in elevated portions of the world that are within either the tropics or subtropics, though it is typically found in mountainous locations in some tropical countries. Despite the latitude, the higher altitudes of these regions mean that the climate tends to share characteristics with oceanic climates, though it also tends to experience noticeably drier weather during the lower-sun "winter" season.
In locations outside the tropics, other than the drying trend in the winter, subtropical highland climates tend to be essentially identical to an oceanic climate, with mild summers and noticeably cooler winters, plus, in some instances, some snowfall. In the tropics, a subtropical highland climate tends to feature spring-like weather year-round. Temperatures there remain relatively constant throughout the year and snowfall is seldom seen.
Areas with this climate feature monthly averages below 22 °C (72 °F) but above −3 °C (27 °F) (or 0 °C (32 °F) using American standards). At least one month's average temperature is below 18 °C (64 °F). Without the elevation, many of these regions would likely feature either tropical or humid subtropical climates. These regions usually carry a Cwb or Cfb designation, though very small areas in Yunnan, Sichuan and parts of Argentina and Bolivia have summers sufficiently short to be Cwc with fewer than four months over 10 °C (50 °F).Copacabana, Bolivia, is one town that features this rare variation of the subtropical highland climate.
This type of climate exists in parts of east, south and southeastern Africa, the exposed areas of High Atlas, some mountainous areas across southern Europe, sections of mountainous North (including higher elevations of the Southern Appalachians), Central and South America, some mountainous areas across Southeast Asia, and parts of the Himalayas. It also occurs in a few areas of Australia, although average high temperatures during summers there tend to be higher and the climate drier than is typical of subtropical highland climates, with summer maxima sometimes exceeding 40 °C (104 °F).
Areas with subpolar oceanic climates feature an oceanic climate but are usually located closer to polar regions. As a result of their location, these regions tend to be on the cool end of oceanic climates. Snowfall tends to be more common here than in other oceanic climates. Subpolar oceanic climates are less prone to temperature extremes than subarctic climates or continental climates, featuring milder winters than these climates. Subpolar oceanic climates feature only one to three months of average monthly temperatures that are at least 10 °C (50 °F). As with oceanic climates, none of its average monthly temperatures fall below -3.0 °C (26.6 °F). Typically, these areas in the warmest month experience daytime maximum temperatures below 17 °C (63 °F), while the coldest month features highs near or slightly above freezing and lows just below freezing. It typically carries a Cfc designation.
This variant of an oceanic climate is found in parts of coastal Iceland, the Faroe Islands, small sections of the Scottish Highlands, the Scottish archipelago of Shetland, northwestern coastal areas of Norway such as Lofoten and reaching to 70°N on some islands, uplands near the coast of southwestern Norway, southern islands of Alaska and northern parts of the Alaskan Panhandle, the far south of Chile and Argentina, and a few highland areas of Tasmania, and the Australian and Southern Alps. This type of climate is even found in the very remote parts of the Papuan Highlands in Indonesia. The classification used for this regime is Cfc. In the most marine of those areas affected by this regime, temperatures above 20 °C (68 °F) are extreme weather events, even in the midst of summer. Temperatures above 30 °C (86 °F) have been recorded on rare occasions in some areas of this climate, and in winter temperatures down to −20 °C (−4 °F) have been recorded in some areas.