<P> The District has 7,464 acres (30.21 km) of parkland, about 19% of the city's total area and the second - highest percentage among high - density U.S. cities . The National Park Service manages most of the 9,122 acres (36.92 km) of city land owned by the U.S. government . Rock Creek Park is a 1,754 - acre (7.10 km) urban forest in Northwest Washington, which extends 9.3 miles (15.0 km) through a stream valley that bisects the city . Established in 1890, it is the country's fourth - oldest national park and is home to a variety of plant and animal species including raccoon, deer, owls, and coyotes . Other National Park Service properties include the C&O Canal National Historical Park, the National Mall and Memorial Parks, Theodore Roosevelt Island, Columbia Island, Fort Dupont Park, Meridian Hill Park, Kenilworth Park and Aquatic Gardens, and Anacostia Park . The D.C. Department of Parks and Recreation maintains the city's 900 acres (3.6 km) of athletic fields and playgrounds, 40 swimming pools, and 68 recreation centers . The U.S. Department of Agriculture operates the 446 - acre (1.80 km) U.S. National Arboretum in Northeast Washington . </P> <P> Washington is in the northern part of the humid subtropical climate zone (Köppen: Cfa) However, under the Trewartha climate classification, the city has a temperate maritime climate (Do). Winters are usually chilly with light snow, and summers are hot and humid . The District is in plant hardiness zone 8a near downtown, and zone 7b elsewhere in the city, indicating a humid subtropical climate . </P> <P> Spring and fall are mild to warm, while winter is chilly with annual snowfall averaging 15.5 inches (39 cm). Winter temperatures average around 38 ° F (3.3 ° C) from mid-December to mid-February . Summers are hot and humid with a July daily average of 79.8 ° F (26.6 ° C) and average daily relative humidity around 66%, which can cause moderate personal discomfort . The combination of heat and humidity in the summer brings very frequent thunderstorms, some of which occasionally produce tornadoes in the area . </P> <P> Blizzards affect Washington on average once every four to six years . The most violent storms are called "nor'easters", which often affect large sections of the East Coast . From January 27 to 28, 1922, the city officially received 28 inches (71 cm) of snowfall, the largest snowstorm since official measurements began in 1885 . According to notes kept at the time, the city received between 30 and 36 inches (76 and 91 cm) from a snowstorm on January 1772 . </P>

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