Csa : C= Temperate s = Dry summer a = Hot summer
These climates usually occur on the western sides of continents between the latitudes of 30° and 45°. These climates are in the polar front region in winter, and thus have moderate temperatures and changeable, rainy weather. Summers are hot and dry, due to the domination of the subtropical high-pressure systems, except in the immediate coastal areas, where summers are milder due to the nearby presence of cold ocean currents that may bring fog but prevent rain.
During summer, regions of the Mediterranean climate are strongly influenced by the subtropical ridge which keeps atmospheric conditions very dry with minimal cloud coverage. In some areas, such as coastal California, the cold current has a stabilizing effect on the surrounding air, further reducing the chances for rain, but often causing thick layers of marine fog that usually evaporates by mid-day. Similar to desert climates, in many Mediterranean climates there is a strong diurnal character to daily temperatures in the warm summer months due to strong solar heating during the day from sunlight and rapid cooling at night.
In winter, the subtropical ridge migrates towards the equator and leaves the area, making rainfall much more likely. As a result, areas with this climate receive almost all of their precipitation during their winter and spring seasons, and may go anywhere from 4 to 6 months during the summer and early fall without having any significant precipitation. In the lower latitudes, precipitation usually decreases in both the winter and summer due to higher evapotranspiration. Toward the polar latitudes, total moisture usually increases; for instance, the Mediterranean climate in Southern Europe has more rain. The rainfall also tends to be more evenly distributed throughout the year in Southern Europe, while in places such as the Eastern Mediterranean, or in Southern California, the summer is nearly or completely dry. In places where evapotranspiration is higher, steppe climates tend to prevail, but still follow the basic pattern of the Mediterranean climates.
Additionally, the temperature and rainfall pattern for a Csa climate can exist as a microclimate in some high-altitude locations adjacent to a rare tropical As (Tropical savanna) climate with dry summers, typically in a rain shadow region, as in Hawaii. These have a favourable climate, with mild wet winters and fairly warm, dry summers.
Csa climates are mainly found around the Mediterranean Sea, southwestern Australia, southwestern South Africa, sections of Central Asia, northern sections of Iran and Iraq, the interior of northern California west of the Sierra Nevada, along the Wasatch Front in Utah, and inland areas of southern Oregon west of the Cascade Mountains. Southern California's coasts also experience hot summers due to the shielding effect of the Channel Islands. However, unshielded areas of that coastline can have warm-summer Mediterranean climates with hot-summer areas just a few kilometres inland.
Köppen–Geiger climate classification map for Mediterranean climate (Cs). Source: Wikicommons. Author: Maulucioni, based on a previous work by Beck, H.E. et al. 2018
Flight safety and planning considerations
Thunderstorms can be accompanied by severe downdrafts and heavy rain causing flooding on airport surfaces and the risk of aquaplaning on runways. Wildfires, with their associated problems, are common in the dry season. High temperatures can have a significant impact on aircraft performance.