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Among major U.S. cities, San Francisco has the coldest daily mean, maximum, and minimum temperatures for June, July, and August. During the summer, rising hot air in California's interior valleys creates a low pressure area that draws winds from the North Pacific High through the Golden Gate, which creates the city's characteristic cool winds and fog. The fog is less pronounced in eastern neighborhoods and during the late summer and early fall, which is the warmest time of the year.
Because of its sharp topography and maritime influences, San Francisco exhibits a multitude of distinct microclimates. The high hills in the geographic center of the city are responsible for a 20% variance in annual rainfall between different parts of the city. They also protect neighborhoods directly to their east ("banana belts" such as Noe Valley) from the foggy and sometimes very cold and windy conditions experienced in the Sunset District; for those who live on the eastern side of the city, San Francisco is sunnier, with an average of 260 clear days, and only 105 cloudy days per year.
Temperatures exceed 75 °F (24 °C) on average only 29 days a year. The dry period of May to October is mild to warm, with average high temperatures of 64–71 °F (18–22 °C) and lows of 51–56 °F (11–13 °C). The rainy period of November to April is slightly cooler, with high temperatures of 58–64 °F (14–18 °C) and lows of 46–51 °F (8–11 °C). On average, there are 73 rainy days a year, and annual precipitation averages 23.6 inches (599.44 mm). Variation in precipitation from year to year is high. In 2013, a record low 5.8 inches of rainfall were recorded in San Francisco (low records were shattered in all of California). Snowfall in the city is very rare, with only 10 measurable accumulations recorded since 1852, most recently in 1976 when up to 5 inches (130 mm) fell on Twin Peaks.
The highest recorded temperature at the official National Weather Service office was 103 °F (39 °C) on July 17, 1988, and June 14, 2000. The lowest recorded temperature was 27 °F (−3 °C) on December 11, 1932. The National Weather Service provides a helpful visual aid graphing the information in the table below to display visually by month the annual typical temperatures, the past year's temperatures, and record temperatures.
San Francisco falls under the USDA 10b Plant Hardiness zone.