San Diego predominantly has a semi-arid warm steppe climate. It enjoys mild, sunny weather throughout the year. Average monthly temperatures range from about 57 Fahrenheit (14 °C) in January to 72 Fahrenheit (22 °C) in July, although late summer and early autumn are typically the hottest times of the year. The average annual daily temperature is 70.5 Fahrenheit. Snow and ice are virtually nonexistent in the wintertime, typically occurring only inland from the coast when present. "May gray and June gloom", a local saying, refers to the way in which San Diego sometimes has trouble shaking off the fog that comes in during those months. Temperatures soar to very high readings only on rare occasions, chiefly when easterly winds bring hot, dry air from the inland deserts (these winds are called "Santa Anas"). The average annual precipitation is less than 12 inches (300 mm), resulting in a borderline arid climate. Rainfall is strongly concentrated in the cooler half of the year, particularly the months December through March, although precipitation is lower than any other part of the U.S. west coast. The summer months are virtually rainless. Rainfall is highly variable from year to year and from month to month, and San Diego is subject to both droughts and floods. Thunderstorms and hurricanes are very rare.
Climate in the San Diego area often varies dramatically over short geographical distances, due to 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 will keep the air cool and damp within a few miles of the coast, but will yield to bright cloudless sunshine between about 5 and 15 miles inland -- the cities of El Cajon and Santee for example, rarely experience the cloud cover. This phenomenon is known as microclimate.