It typically lacks a dry season, as precipitation is more evenly dispersed throughout the year. It is the predominant climate type across much of Western Europe, the Pacific Northwest region of the United States and Canada, portions of central Mexico, southeastern South America, southeastern Australia, including Tasmania, New Zealand as well as isolated locations elsewhere. Oceanic climates generally have warm summers and cool (but not cold) winters. They are characterised 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 humid subtropical. 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 in an oceanic climate must have at least 40 millimeters per month. All months must have adequate rain and cloudy conditions are common in oceanic climates. London is an example of an oceanic climate. It experiences reliable and constant precipitation throughout the entire year. Despite this, thunderstorms are quite rare since hot and cold air masses meet infrequently in the region. 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. Most oceanic climate zones, or at least a part of them, experience at least one snowfall 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 0 °C (32 °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). 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 (for their latitude) 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 fog, 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 Northwest coast of America, bathed by the Pacific Ocean).