tallest building in San Diego is One America Plaza, standing tall, which was completed in 1991. The downtown skyline contains no super-talls, as a regulation put in place by the Federal Aviation Administration in the 1970s set a limit on the height of buildings within a radius of the San Diego International Airport. An iconic description of the skyline includes its skyscrapers being compared to the tools of a toolbox. There are several new high-rises under construction, including two that exceed 400 feet (122 m) in height. Climate San Diego has one of the top-ten best climates in the United States, according to the Farmers' Almanac and has one of the two best summer climates in the country as scored by The Weather Channel. Under the Köppen–Geiger climate classification system, the San Diego area has been variously categorized as having either a semi-arid climate (BSh in the original classification and BSkn in modified Köppen classification with the n denoting summer fog) or a Mediterranean climate (Csa). San Diego's climate is characterized by warm, dry summers and mild winters, with most of the annual precipitation falling between December and March. The city has a mild climate year-round, with an average of 201 days above and low rainfall ( annually). The climate in San Diego, like most of Southern California, often varies significantly over short geographical distances, resulting in microclimates. In San Diego, this is mostly because of the city's topography (the Bay, and the numerous hills, mountains, and canyons). Frequently, particularly during the "May gray/June gloom" period, a thick "marine layer" cloud cover keeps the air cool and damp within a few miles of the coast, but yields to bright cloudless sunshine approximately inland. Sometimes the June gloom lasts into July, causing cloudy skies over most of San Diego for the entire day. Even in the absence of June gloom, inland areas experience much more significant temperature variations than coastal areas, where the ocean serves as a moderating influence. Thus, for example, downtown San Diego averages January lows of and August highs of . The city of El Cajon, just inland from downtown San Diego, averages January lows of and August highs of . The average surface temperature of the water at Scripps Pier in the California Current has increased by almost since 1950, according to scientists at Scripps Institution of Oceanography. Additionally, the mean minimum is now above , putting