Cfb: C = Warm temperate f = Fully humid b = Warm summer
An oceanic climate, also known as a marine climate, is the humid temperate climate sub-type, in Köppen classification Cfb, typical of west coasts in higher middle latitudes of continents, generally featuring cool summers and mild winters (for their latitude), with a relatively narrow annual temperature range and few extremes of temperature. Oceanic climates can be found in both hemispheres generally between 40 and 55 latitude, most notably in Northwest Europe, Northwest North America, as well as Tasmania and New Zealand.
Locations with oceanic climates tend to feature frequent cloudy conditions with precipitation, low hanging clouds, and frequent fronts and storms. Thunderstorms are normally few, since strong daytime heating and 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. Severe weather is rare.
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 or higher in the coldest month, compared to continental climates where the coldest month has a mean temperature of below 0°C in the coldest month. Summers are warm but not hot, with the warmest month having a mean temperature below 22°C. Poleward of the latter is a subtype of it and is the 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 for one to three months). The infrequent temperature extremes -- hot is summer, cold in winter -- can occur when the typical marine air is replaced by drier continental air.
The polar jet stream, which moves in a west to east direction across the middle latitudes, advances 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 cool ocean adjacent to them. In the autumn, 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 North America, bathed by the Pacific Ocean.
The North Atlantic Gulf Stream, a tropical oceanic current that passes north of the Caribbean and up the East Coast of the United States to North Carolina, then heads east-northeast as the North Atlantic Current, is thought to greatly modify the climate of Northwest Europe. As a result, west coast areas located in high latitudes like Ireland, the UK, and Norway have much milder winters (for their latitude) than would otherwise be the case. The lowland attributes of western Europe also help drive marine air masses into continental areas, enabling cities such as Dresden, Prague, and Vienna to have maritime climates in spite of being located well inland from the ocean.
Köppen–Geiger climate classification map for oceanic climate - source: wikicommons, authors: Beck, H.E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F., 2018
Flight safety and planning considerations
Low pressure systems bring low cloud, precipitation, strong winds and associated turbulence. Contaminated runways and strong cross-wind conditions increase risk of runway excursions. In-flight icing in frontal cloud can be a threat to aircraft safety, especially in the winter. Static high pressure systems in winter are often associated with fog, which may persist for several days.
Koppen climate classification system (KCC)