The geography of southern California refers to the geography of southern California in the United States. Climate Despite the popular image of California as a place of sunshine and perfect weather, the local climate can be very diverse, with some areas experiencing more extreme conditions. However, the weather in the region is usually mild, especially in the winter, and dry, with rainfall ranging from moderate in the coastal regions to almost none at all in the desert. Around the coastal areas, the weather does not vary as dramatically as it does inland. Climate is affected by factors such as latitude, topography, and proximity to water masses - primarily the Pacific Ocean, and southern California's mountain ranges. The Transverse Ranges and the Peninsular Ranges are key players in the region's climate. Essentially, the mountain ranges separate southern California into two distinct climatic regions: The heavy-populated coastal area west of these mountains is the one most associated with the term "southern California" and is characterized by pleasant weather all-year round, without frequent heat spells in the summer and without low temperatures in winter. By comparison, the area east of the ranges, between the mountains and the borders with Nevada and Arizona, is dominated by the Sonoran Desert and the Mojave Desert and tends to be more arid and register more extreme temperatures in both summer and winter. Low clouds and fog This is a common weather prediction for southern California. Due to the topographic features and proximity to the Pacific, southern California has its share of both low clouds and fog. Coastal fogs are frequently generated by interaction between seasonal inversion layers and the coastal marine layer, and may reach as far inland as 20 miles, butting up against inland mountains or coastal mountain ranges. While fog generally is the collection of water droplets or ice crystals suspended in the air at or near the Earth's surface, southern California's fog varies from the light 'ground fogs' to a dense almost "Tule fog" (pronounced ˈtuːliː fog) in the Winter and Spring, depending on the interaction of cold air brought down from the local mountains and the warmer ocean air masses. However, over the last few decades, clouds have become less prevalent on the coast, due to urban heat and climate change. When compared with data from the 1970s, scientists discovered that the stratus cloud cover has decreased between 25% and 50%. "May Gray"